Sky & Telescope - July 2013

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Dynamic Planet: Key to Life? p. 18

Much Ado About Dew p. 30

Great Summer Galaxies p. 56

Why To Build Your Own Scope p. 66

Find Barnard’s Star p. 48

Better Photos with Modifi ed DSLRs p. 68

T H E E S S E N T I A L G U I D E TO A S T R O N O M YT H E E S S E N T I A L G U I D E TO A S T R O N O M Y

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July 2013 VOL. 126, NO. 1

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On the cover: The Milky Way’s dusty plane stretches across the sky seen from Mount Uludag in Turkey.PHOTO: TUNÇ TEZELINSET: FILIPPO_JEAN / FOTOPEDIA

OB SERVING JULY

38 Northern Hemisphere’s Sky By Fred Schaaf 39 July’s Sky at a Glance

40 Binocular Highlight By Gary Seronik

41 Special Foldout: Map of the Milky Way Photo by Serge Brunier 45 Sun, Moon & Planets By Fred Schaaf

47 Planetary Almanac

48 Celestial Calendar By Alan MacRobert

52 Exploring the Solar System By John E. Bortle

56 Deep-Sky Wonders By Sue French

60 Going Deep By Steve Gottlieb S&T TE S T REPORT

62 S&T Test Report By Dennis di Cicco

AL SO IN THIS ISSUE

6 Spectrum By Robert Naeye

8 Letters

9 75, 50 & 25 Years Ago By Roger W. Sinnott

10 News Notes

36 New Product Showcase

66 Telescope Workshop By Gary Seronik

72 Gallery

82 Focal Point By Howard J. Brewington

SKY & TELESCOPE (ISSN 0037-6604) is published monthly by Sky & Telescope Media, LLC, 90 Sherman St., Cambridge, MA 02140-3264, USA. Phone: 800-253-0245 (customer service/subscriptions), 888-253-0230 (product orders), 617-864-7360 (all other calls). Fax: 617-864-6117. Website: SkyandTelescope.com. © 2013 Sky & Telescope Media, LLC. All rights reserved. Periodicals postage paid at Boston, Massachusetts, and at additional mailing offi ces. Canada Post Publications Mail sales agreement #40029823. Canadian return address: 2744 Edna St., Windsor, ON, Canada N8Y 1V2. Canadian GST Reg. #R128921855. POSTMASTER: Send address changes to Sky & Telescope, PO Box 420235, Palm Coast, FL 32142-0235. Printed in the USA.

FE ATURE S

18 Is Plate Tectonics Necessary for Sentient Life? Water, atmosphere, and pleasant temperatures are nice, but active geology could make or break a planet’s habitability. By Bruce Dorminey

24 Observing the Milky Way, Part I: Sagittarius & Scorpius Binoculars are the ideal tool for exploring the galaxy we call home.

By Craig Crossen

30 Dew Busting Dew can form suddenly and almost without warning. Here’s how to stop it from ruining a nice night under the stars. By Rod Mollise

68 Shooting with Modifi ed DSLR Cameras Expanding the spectral response of your camera opens up many new imaging opportunities. By Hap Griffi n

COVERSTORY

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4 July 2013 sky & telescope

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on April 16th, the day after the Boston Marathon bombings that left multiple people dead and more than 180 injured. This tragedy hits home for the S&T staff because it took place right across the Charles River from our Cambridge offi ces. Fortunately, nobody on our staff was directly aff ected, but our heartfelt condolences go out to the victims and their families. I am deeply saddened that the Boston Marathon — a truly inter-national event — was wracked by violence and will never again be the same.

In the wake of this tragedy, there are no words that I can summon to smoothly transition to a diff erent topic. But there are some much brighter notes at S&T. A few days ago I returned from our highly successful Iceland Aurora Adventure, run in partnership with Spears Travel. Our tour group had about 90 people, mostly from the U.S. but also from other nations such as Canada and Brazil. During the daytime we had a wonderful time explor-

ing Reykjavik, geothermal areas, caves, waterfalls, etc. (see my photo on page 23), and on the fi nal two nights we enjoyed interesting and rapidly chang-ing aurora displays. Many tour-group members captured beautiful photos showing green and reddish auroral emission. We look forward to November’s Kenya total solar eclipse trip and next year’s expedition to Chile.

I’m also very pleased to announce the sophisticated new MarketPlace sec-tion on our website (www.marketplace.skyandtelescope.com). The site enables amateur astronomers, manufacturers, and dealers to meet in cyberspace to buy and sell equipment across more than 60 diff erent product categories.

Individuals who want to sell astronomical gear can place an ad for a used item for just $5. The ad will remain on our site for a full year, or until the stuff is sold. If you want to purchase equipment, you can look for great deals on a wide variety of products, including new, used, refurbished, and blem-ished items. A comprehensive search function makes it easy to fi nd whatever type of equipment interests you. You can also register to receive e-mail alerts whenever a new product becomes available in a category of interest and that matches your saved search criteria. Whether or not you’re interested in buy-ing or selling a piece of gear right now, check out MarketPlace! ✦

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Letters

Write to Letters to the Editor, Sky & Telescope,90 Sherman St., Cambridge, MA 02140-3264,

or send e-mail to [email protected] limit your comments to 250 words.

Loony for Larrieu’s DamI was excited to see the article on Larrieu’s Dam in the March issue (page 54), since I had just “discovered” it for myself barely two weeks before! While on vacation in warmer climes, I was scanning the lunar terminator on the evening of January 17th using my cherished LOMO Astele 150 Mak, at about 80×. I was startled by a clearly vis-ible, straight-line feature, exactly where it’s marked on the image in the article.

I asked others to confi rm what I saw in the eyepiece, and they did. I was sure it was just a transient pattern of light and shadow and thought that perhaps someday I might try to fi nd out if anyone else had reported it. In the bustle of returning home I forgot all about it — until S&T showed up in my mailbox barely a week later with the whole story. Talk about timely information!

By the way, you can also re-create the dam using software or a good lunar smart-phone app, although it pales to the sublime experience of seeing the real thing.

Dave RunyanBainbridge Island, Washington

Exoplanets? There’s an App for ThatAs part of my outreach as an astrophysicist I’ve created an iPhone app called Exoplanet, which I think might be of interest to your readers. The app keeps users informed of exoplanet discoveries, with a news section listing the latest announcements and web-links to the discoverers’ research papers. It also includes an interactive model of the Milky Way with animations of the planetary systems that we have found so far. I’m not running this as a business: the basic app is free and I just want to engage the public. It can be downloaded from the iTunes store at http://bit.ly/OY4pBi.

Hanno ReinPrinceton, New Jersey

Enigmatic EthaneThe large deposits of ethane suggested to be on Titan as lakes (March issue, page 26) have intrigued me as a chemist. Assuming that methane-to-ethane photo-chemistry occurs at these distances from the Sun, the primary photodissociation mode in light with wavelengths between 129 to 147 nm (the methane absorption band) is the elimination of molecular hydrogen and the formation of a divalent carbon called methylene. But ethane has a similar strong absorption band in the same wavelength region as methane. It too should produce molecular hydrogen and a divalent carbon species. Therefore, ethane should not be stable to photochem-istry. So why should ethane not behave like methane?

Francis J. WallerAllentown, Pennsylvania

Editor’s Note: The shortest answer is that ethane is close to four orders of magnitude less abundant than methane is in Titan’s atmosphere. Therefore its photolysis is rather insignifi cant, even though on the surface (where no molecule-tearing ultraviolet radia-tion reaches) it may accumulate and — at least for the moment — dominate. In addi-tion, the main ethane photolysis pathway isn’t direct; rather, it’s catalyzed by another hydrocarbon. That might further hamper ethane’s breakdown.

Not So Big After AllRegarding the April issue’s Focal Point “We’re Actually Quite Big” by David Kan-torowitz (page 86), our size is not halfway between almost zero and 1027 meters. In fact, 1026 meters is only one-tenth of the way along that continuum, and 5× 1026 is halfway. I’m sure the article was written tongue-in-cheek, but it trivialized the magnitude of exponential functions.

Thomas C. Mosca IIIWarsaw, Virginia

I enjoyed Kantorowitz’s article and his comparison of humans’ physical size to the small and large constituents of our realm of existence. However, when most people refer to being “miniscule” (or “small”) it is not from a physical size perspective but from a cosmic viewpoint. If our Sun should suddenly cease to exist, our galaxy would never notice; and if our galaxy should suddenly vanish, the observable universe wouldn’t care; and if our observable universe should magically disappear, the “grand universe” (in which the observable universe is but a vanish-ingly insignifi cant member) would not be bothered at all; and if our “grand uni-verse” went AWOL, it would not create the faintest whisper within the multiverse.

As a retired nuclear engineer, I feel small whenever I contemplate the unfath-omable vastness of the cosmos. I also feel

High in the northern hemisphere of Saturn’s moon Titan, this lake’s islands look like extensions of a fl ooded mountain ridge. The black in this Cassini radar image is probably liquid tens of meters deep.

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July 1938Stellar Furnaces “It is incorrect to think of the sun [or any other star] as being on fi re, for it is so hot, even at its surface, that the chemical combination which we call fi re cannot take place. . . . The only present

theory which seems to fi t the facts is that the stars are giant converters — changing matter into radiant energy. . . .

“Our newspapers daily attest the fact that research scientists everywhere are devoting the greater portion of their eff orts to the problems of the structure of the atom and the release of sub-atomic energy.”

A few months after Sky & Telescope founder Charles A. Federer, Jr., wrote this article, Otto Hahn, Lise Meitner, and their colleagues achieved (and explained) nuclear fi ssion. Around this same time, Hans Bethe proposed that nuclear fusion could power the stars.

July 1963Planet of Barnard’s Star “During the past 25 years, our systematic photogra-phy of Barnard’s star has continued at an average of nearly 100 plates a year. . . . [Measurements] indicate that Barnard’s star is shifted by the gravitational

attraction of an unseen companion. . . .“The exceptional character of this binary

system becomes clear when we consider . . . that the mass of the unseen companion is only about 0.0015 sun — a mere 1½ times as massive as Jupiter! Such an object must be

regarded as a planet rather than a star.”Astrometric authority Peter van de Kamp

described his fi nd with the Sproul Observatory 24-inch refractor in much the way exoplanet hunt-ers do today. But his tiny, 24-year oscillation was not confi rmed at other observatories and is now blamed partly on a tiny change in the telescope’s imaging properties after the lens cell was replaced in 1949. More on Barnard’s Star on page 48.

July 1988Light Probes “On April 30, 1006, the brightest supernova in recorded history burst into view in the southern constel-lation of Lupus. The brilliant new star prob-ably reached apparent magnitude –8 or –9, far

outshining Venus and casting shadows. . . .“No stellar remnant has been detected, but,

by chance, a rare and unusual star lies almost directly behind the center of the [expand-ing debris] remnant. This lucky break gives astronomers a chance to use this starlight to probe inside the explosion cloud. . . .

“The recent results [with the International Ultraviolet Explorer satellite] are exciting because the ejecta’s observed velocities and composition are just those predicted by models of a Type Ia supernova. . . . However, there is one problem with this picture — where is the 0.35 solar mass of iron such a supernova sup-posedly produces? X-ray observations show no evidence of it, and only about 0.015 solar mass shows up in the IUE spectra.”

Observed a few years ago with the Hubble Space Telescope, additional background stars behind the remnant revealed more iron, but still not enough to match Type Ia models.

equally as small whenever I contemplate the bizarre laws of quantum mechanics, which govern the realm of the subatomic world and which are in total confl ict with the common sense that governs the world I live in.

Frank RidolfoBloomfi eld, Connecticut

Liquid Mirror’s Long HistoryAs hinted in April’s article on liquid-mirror telescopy (page 26), rotating mercury mir-

75, 50 & 25 Years Ago Roger W. Sinnott

rors aren’t new. A 1970 article in Amateur Telescope Making recounts the experiments of Robert Wood (Johns Hopkins Univer-sity) around 1909, which are also discussed in the August 1991 Journal of the Royal Astronomical Society of Canada. That article takes a detailed look at liquid mirrors in the last 150 years and highlights Ermanno Borra’s work (mentioned in the April S&T). It’s available at http://bit.ly/10Qc9aC.

Peter L. AlbrechtCosta Mesa, California

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News Notes

EXOPLANETS I Almost Earth-like WorldsThis illustration depicts Kepler-62f, a super-Earth-size planet in its star’s habitable zone. The bright white “star” to the planet’s lower right represents another poten-tially habitable planet, Kepler-62e. Astronomers don’t know the mass of either world.

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NASA’s Kepler mission has discovered a fi ve-planet system that includes a “hot Mars” and four super-Earths, two of which might host liquid water. These aren’t quite the Earth-like exoplanets Kepler has been looking for, but they’re close.

The Kepler-62 system lies 1,200 light-years away around an orange, hydrogen-fusing K2 star about two-thirds the size of our Sun. The hot Mars whips around the star every 12 days; two hot super-Earths complete orbits every 6 days and 18 days. The fi nal two worlds, Kepler-62e and Kepler-62f, are 60% and 40% bigger than Earth, respectively, and their orbits last 122 days and 267 days, William Borucki (NASA/Ames Research Center) and his team reported online April 18th in Science.

Yet despite the media fanfare, astrono-mers proceed with caution. “I’d be hesi-tant to call any of these worlds potentially ‘Earth-like,’” says Caleb Scharf (Colum-bia University), an exoplanet expert not involved in the study. “But their discovery is defi nitely leading us closer and closer to places that might represent alien, but none-theless similar, environments to our own.”

The Holy Grail of exoplanet searches is fi nding an Earth-size planet in a star’s habitable zone, but that’s more easily defi ned in words — “the region around a star where a rocky planet with an atmo-sphere could host liquid water on its sur-

face” — than in practice. Borucki’s team used two approaches to defi ne Kepler-62’s habitable zone. The fi rst assumes the plan-ets are rocky, with atmospheres thick with water vapor and carbon dioxide. Under these strict assumptions, Kepler-62f would receive enough stellar fl ux to keep liquid water on its surface, with the help of greenhouse eff ects. Kepler-62e would be too hot.

A more liberal approach defi nes the

habitable zone by referring to the orbits and atmospheres Venus and Mars had billions of years ago, when they were still able to host liquid water. This method allows Kepler-62e to sneak in.

Even if we take the latter tack, are the planets actually habitable? Their masses are too low to nail down via radial veloc-ity or variations in the transit timings, so with just their sizes astronomers can only speculate about what they’re made of. Still, by not fi nding these other signals, the team can limit Kepler-62e to 36 Earth masses and Kepler-62f to 35 Earth masses.

If the planets are both rocky and many times Earth’s mass, they might be very geologically active. Then again, since Kepler-62 is 7 billion years old, the planets could have simmered down by now.

On the other hand, an Earth-mass water world could have an ocean, but deep down it would turn into pressurized ice.■ MONICA YOUNG

The inner solar system’s planets are compared with those of the Kepler-62 system, which lies about 1,200 light-years away in Lyra.

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News Notes

On April 10th the space agency’s managers unveiled a proposal to capture a small, as-yet-unidenti-fi ed asteroid, drag it back to Earth’s vicinity, and send astronauts to work on it — all within the next decade.

Before that announcement, new plans for near-Earth object (NEO) study and mining had come mostly from the private sector (May issue, page 16). The mindset has been that private investors can ante up far more dollars

Our neighborhood just got a little more crowded. Two newly discovered brown dwarfs lie about 7 light-years away, making them the closest brown dwarfs known and maybe the third-closest star system known.

The binary, WISE J104915.57–531906, appears in data from NASA’s now-hibernating Wide-fi eld Infrared Survey Explorer (WISE). It joins Alpha Centauri (4.4 light-years away), Barnard’s Star (6.0 light-years), and Wolf 359 (7.8 light-years) as the nearest star systems to Earth and is the closest system discovered since 1916. Kevin Luhman (Penn State University) announced the discovery in the April 10th Astrophysical Journal.

Previous studies have found brown dwarfs by their infrared colors, but Luh-man searched for infrared sources with high proper motion. He caught a dim but rapidly moving object in the WISE surveys and calculated where he might fi nd it in older infrared surveys taken between 1978

The third closest star system to Earth, WISE J1049 is the bright orb at the center of the larger image, taken by WISE. A sharper image from the Gemini South telescope (inset) reveals that the object is actually a binary.

for NEO exploration than NASA can muster.But the President’s proposed 2014 budget

includes an eye-popping plan to kick asteroid utilization into high gear. The $105 million in start-up funding for this new initiative is one of the few bright spots in a $17.7-billion proposal that slashes overall spending for solar-system science by nearly 20%.

The retrieval plan has three phases:• Stepped-up searches for small bodies, with an eye toward fi nding one with a mass

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of roughly 500 tons (up to 35 feet, or 10 meters, across) in an Earth-like orbit. The budget includes a doubling of the funds — to $40.5 million — currently set aside for NEO searches and follow-up observations.• An ion-propelled spacecraft dispatched to bag the object and drag it back to a gravita-tionally stable location near Earth.• Astronauts using the Orion capsule and SLS launch system (now under development), will rendezvous with the asteroid and gather samples. First footfall would be as early as 2021, before President Obama’s astronauts-to-asteroid deadline of 2025.

In some ways, the proposal off ers some-thing for everyone, says Senator Bill Nelson (D-Florida). “The plan combines the science of mining an asteroid, along with developing ways to defl ect one, along with providing a place to develop ways we can go to Mars.”

The plan is still sketchy, but it draws heavily on concepts detailed last year by a study for Caltech’s Keck Institute for Space Studies. A more thorough review of the mission concept is still several months away.■ J. KELLY BEATTY

STARS I Closest Brown Dwarf System Discoveredand 1999. The combined detections give a parallax of 0.5 arcsecond, or a distance of 6.5±0.5 light-years, putting the system just past Barnard’s Star (page 48).

Independent work by Alexei Kniazev (South African Astronomical Observatory) and his colleagues confi rms the distance is from 6 to 9 light-years, based on the objects’ brightnesses.

Both studies peg the brown dwarfs near the transition between the two lowest stellar classes, L and T. Separated by three times the Earth-Sun distance, one brown dwarf is about 1.5 times brighter than the other.

“This pair of brown dwarfs is so bright because of its close proximity to us that, when I fi rst started examining it, I thought that it was surely too bright to be a brown dwarf,” Luhman says. The pair has gone undetected until now because previous surveys tend to avoid the Milky Way’s star-dense plane.■ SHARAZADE BALOUCHI

To get astronomy news as it breaks, visit skypub.com/newsblog.


NASA managers have announced plans (illustrated here) to corral a near-Earth asteroid and bring it back to Earth’s vicinity.

MISSIONS I NASA Plans Asteroid Snag


SKY Ads.indd 13 4/26/13 3:46 PM

Astronomers have discovered a new, milder class of supernova in which the star might survive the explosion. Ryan Foley (Harvard-Smithsonian Center for Astro-physics) and his team collected observa-tions old and new of 25 supernovae that look almost — but not quite — like their Type Ia brethren, explosions in which a white dwarf grabs too much material from a companion star and explodes.

The 25 supernovae share a dozen or so properties that distinguish them from normal Type Ia events, including lower peak brightnesses and lower ejecta veloci-ties. Foley and his colleagues have dubbed these supernovae Type Iax.

These supernovae also result from thermonuclear fusion that starts deep within a white dwarf. But the reaction fails to demolish the entire star; instead, only a half Sun’s worth of material (on average) is ejected, including ash from the thermo-

SUPERNOVAE I New Type of Exploding Dwarf . . .

At more than 10 billion years old, a Type Ia supernova dubbed “Wilson” is the oldest and most distant discovered of its kind. Wilson lies at a redshift of 1.9 and is now the farthest marker on the super-nova-based cosmic yardstick with which astronomers measure both distances in the universe and the cosmic expansion rate.

Offi cially named SN UDS10Wil, the new record-breaker comes from the CANDELS+CLASH Supernova Project, a near-infrared observing campaign survey-ing the early universe with the Hubble Space Telescope. The discovery team is naming the supernovae they fi nd after U.S. presidents; this one is named for Woodrow Wilson.

“We’ve never seen an object like this so early in the universe,” says coauthor David Jones (Johns Hopkins University), whose study appeared in the May 10th Astrophysical Journal. “The exciting part is we haven’t found more of them.”

Jones and his colleagues think that the dearth of supernovae like Wilson in the early universe is an important clue to the origin of these massive explosions.

Type Ia supernovae are the demolitions of overweight white dwarfs, but astronomers disagree whether white dwarfs fatten up by sucking matter off a swollen, aging com-panion star or by merging with a second white dwarf. Observational evidence backs up both scenarios.

The star-sucking model produces supernovae promptly and consistently. Thus, if most Type Ia’s happen this way, the universe’s supernova production line comes online around the same time that the early universe is making vast amounts of stars — meaning there ought to be many supernovae at Wilson-esque ages.

But if colliding white dwarfs are the cul-prits, the universe’s supernova production line turns on abruptly, when the tightest-orbiting binary systems begin colliding. The abruptness would mean that, as astronomers look farther into the early uni-verse, the number of supernovae should drop precipitously, with vast numbers of stars sitting around waiting for the assem-bly line to start up. This is what Wilson’s forlorn presence seems to suggest.■ MARK ZASTROW

. . . and the Oldest, Loneliest Supernova

nuclear burning. Often, some part of the white dwarf may survive the defl agration.

“The proposed explanation . . . fi ts many of the observed properties,” says Craig Wheeler (University of Texas at Austin), who was not involved in the study. “Model-ing of these events is nevertheless a new art and probably deserves maturing before fi rm conclusions are reached,” he cautions.

The team estimates in an upcoming Astrophysical Journal that the new class is about one-third as common as regular Type Ia supernovae. But are these explo-sions worthy of the supernova title if they fail to destroy the star? “My take,” Foley says, “is that (1) some of these objects may in fact completely disrupt their star, and (2) in every way except for the possibility of the remaining star, SNe Iax are more like supernovae than novae. Maybe we need a new word. ‘Pretty good’ novae?”■ MONICA YOUNG

After a prolonged search, a group of Russian space enthusiasts thinks it has fi nally spotted the remains of the Soviet Mars 3 lander. Mars 3 fell silent seconds after landing in 1971, and its exact location in the broad crater Ptolemaeus at 45° S, 158° W was uncertain. Led by Vitaliy Egorov, the group combed through images taken in 2007 by the NASA Mars Reconnaissance Orbiter’s HiRISE camera and found objects on the surface that appear to be the lander and its heat shield, retrorocket, and para-chute. A follow-up image taken on March 10th supports the interpretation. ■ J. KELLY BEATTY

Astronomers have detected what might be the farthest star spectroscopi-cally observed. Using optical and ultraviolet observations, Youichi Ohyama (Academia Sinica, Taiwan) and Ananda Hota (UM-DAE Centre for Excellence in Basic Sciences, India) have pinpointed a suspicious object 55 million light-years away. Named SDSS J122952.66+112227.8, the object is a bright bluish blob in the clumpy gas tail of the galaxy IC 3418. Its spectral fi ngerprints match those of an evolved O-type star, the duo reported in the April 20th Astrophysi-cal Journal. If it’s a star, J1229 could help researchers understand star formation in exotic locales, far from the calm, cold molecular clouds nestled inside galaxies.■ CAMILLE M. CARLISLE

Since its discovery in 2004, asteroid 99942 Apophis has worried celestial dynamicists because of its potential for an Earth-devastating wallop. Recent radar observations made an impact in 2036 highly unlikely (April issue, page 10). Yet the asteroid’s orbit might have been tweaked by the Yarkovsky eff ect, the gentle but per-sistent nudging that occurs when absorbed sunlight is reradiated by a rotating object. Further analysis allays that concern: Apophis is both elongated and tumbling, character-istics that minimize the eff ect. There’s now zero chance of a 2036 impact and a mere 0.0002% chance of impact in 2068. ■ J. KELLY BEATTY

IN BRIEF

News Notes



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News Notes

DARK MATTER I Homing in on Mystery Particles?In April an international team working deep in a Minnesota mine announced the detection of what might be three dark matter particles scattering off atoms in silicon wafers. These three events do not constitute a discovery: with a statistical signifi cance of three sigma (science-speak for “pretty good but no cigar”), the detec-tions could be background noise.

Still, the Cryogenic Dark Matter Search (CDMS) collaboration’s result intrigues researchers. “This result looks about as solid as three events could — but then again it’s only three events,” says Dan Hooper (Fermilab), who was not involved with the new study. “It’s an interesting hint, made even more interest-ing because of the similar signals seen in other experiments.”

Those similar signals and the new CDMS result both imply a particle mass of about 10 gigaelectron volts. (If you could convert a proton’s entire mass into energy, it would take about 10 protons to make a GeV.) That would put the particle on the lightweight end of what’s expected

for weakly interacting massive particles (WIMPs), the current favorite for the universe’s primary-yet-invisible matter constituent (January issue, page 26).

Notably, this mass is at most one-hun-dredth of what’s implied by another result announced two weeks earlier, says Hooper. In that study, physicists using the Alpha Magnetic Spectrometer (AMS) aboard the International Space Station measured an excess in positrons that, they suggested, might be a byproduct of dark matter par-ticles colliding and annihilating.

The CDMS experiment is lodged about a half mile underground in the Soudan Underground Laboratory. Its second-generation run, CDMS II, worked from 2003 to 2008 and used cryogenically cooled silicon and germanium wafers, stacked into little towers, to look for pass-ing dark matter particles. If dark matter particles are whizzing by, every once in a while one should collide with an atom in the detectors, making the nucleus recoil and give off heat. Because silicon atoms are less massive than germanium’s, they react more when lower-mass particles hit them than germanium atoms do. Eight of the experiment’s 11 silicon detectors were analyzed by Rob Agnese (University of Florida) and his colleagues. Their study will appear in Physical Review Letters.

The mass pinpointed by CDMS II, 8.6 GeV, also agrees with one suggested by a faint gamma-ray haze teased out by Hooper and his colleagues from observa-tions by NASA’s Fermi Gamma-ray Space Telescope. Hooper thinks that haze might be from dark matter annihilation. There’s remarkable agreement between the Fermi residue and what’s expected for dark matter, but the signal could also be from millisecond pulsars, says Kevork Abazajian (University of California, Irvine).

So what will it take to “discover” dark matter? Gamma-ray detections from dwarf galaxies (which have a lot of dark matter and probably not a lot of millisec-ond pulsars) would help. So might future results from CDMS’s next iteration or other ground-based experiments, such as LUX in South Dakota. ✦■ CAMILLE M. CARLISLEFE

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CDMS scientists remove one tower of detec-tors used in the Cryogenic Dark Matter Search experiment. Data from a 2003-2008 CDMS run, called CDMS II, contain three signals that might be from dark matter particles hitting atoms in the experiment’s detectors.

Astronomers are closer to understand-ing how fl uff y, multi-armed spiral galaxies grow their whirls. Elena D’Onghia (Uni-versity of Wisconsin, Madison) and her colleagues followed disks of 100 million star particles in computer simulations and then added in some molecular clouds. The clouds’ presence triggered clumping into ragged arms and, contrary to previous thinking, these arms self-perpetuated by triggering more arms, even after the clouds were gone, the team reported in the March 20th Astrophysical Journal. The result could explain the less prominent arms of so-called fl occulent spirals.■ CAMILLE M. CARLISLE

Millimeter-wavelength observations of the Milky Way’s chaotic center show hints of stars forming just 2 light-years from our galaxy’s supermassive black hole. The beast wreaks gravitational havoc on its surroundings, and astronomers have wondered if nearby young stars formed in situ or migrated in. Reporting in the April 20th Astrophysical Journal, Farhad Yusef-Zadeh (Northwestern University) and his colleagues found 11 clumps of silicon oxide, which typically appears in the warm, dense environments around forming stars. But collisions between fast-moving clouds could also make the clumps glow, with no stars needed. If protostars hide inside, normal star formation might be ongoing near the black hole.■ MONICA YOUNG

There’s a new class of gamma-ray bursts. Unlike long GRBs, which last several seconds to a few minutes, three events detected by NASA’s Swift satellite lasted 30 minutes to several hours. The durations, coupled with unique aspects of the bursts’ light curves, prompted Andrew Levan (Uni-versity of Warwick, UK) and his team to call them “ultra-long GRBs.” Like long GRBs, ultra-longs might be jets created when massive stars die and birth a black hole, but ultra-longs would come from stars with extremely wide girths. The dying gasp of a star eaten by a black hole (June issue, page 16) could also be to blame.■ MONICA YOUNG




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Planetary Shake, Rattle, ‘n’ Roll

The very geodynamics that move mountains, spawn tsunamis, and reduce cities to mere rubble might ultimately hold the key to the evolu-tion of intelligent life in the universe. For all the furor over whether we are the only sentient beings in the galaxy, the geophysical force known as plate tectonics is arguably the most under-

appreciated factor in the astrobiological equation.Unless intelligent life can exist as amorphous blobs

lurking in interstellar clouds, it needs terra fi rma. But it also needs more than that — and that “extra something” comes in part from plate tectonics. So if we understand why Earth is the only planet in our own solar system with global plate tectonics, we can better understand what types of planets might ultimately harbor advanced life.

But grasping the evolution of “life as we know it” requires a deep understanding of plate tectonics’ role in shaping Earth’s geography, its climate, and the dynamic geological forces that ultimately led to our planet’s extraordinary biological diversity, an understanding scien-tists are still amassing.

Lessons from Venus and MarsThe interiors of newborn planets are brimming with radioactive nuclides such as uranium, thorium, and

Is Plate TectonicsBruce Dorminey

potassium. Planets slowly radiate the heat from the decay of these nuclides and from the worlds’ initial formation into space, mostly through volcanism.

On Earth, this mechanism manifests itself in the form of a global system of fractured, rigid plates (see facing page). The plates literally slide horizontally over the upper mantle. These plates, composed of a combination of the upper mantle and surface crust, inevitably collide with and subduct (slide and sink) under other plates. These slow but inexorable processes create mountain ranges such as the Andes and deep-ocean ridges and trenches, such as the Mariana Trench.

Destructive earthquakes occur frequently at plate boundaries, but the force of tectonic subduction also plays a creative role by recycling carbon dioxide (CO2). Subduc-tion depletes this greenhouse gas from the atmosphere and acts as a built-in thermostat, enabling Earth to maintain habitable temperatures over billions of years. In other words, our current habitable atmosphere ultimately depends upon plate tectonics.

But planets need more than heat to drive plate tecton-ics. Without Earth’s plethora of water to promote subduc-tion, plate tectonics wouldn’t have gotten very far. Water alters the minerals in rocks into weaker compounds — changing basalt into soft, mushy talc, for example — which enables the tectonic plates to slide along smoothly next to one another. Without that kind of water-inducing

Rough locations for Earth’s continents over time

250 million years ago 200 million years ago 150 million years ago (based on one model) supercontinent breaks up North America breaks away

Sentient Life?


Plate Tectonics.indd 18 5/2/13 9:38 AM

Necessary for Water, atmosphere, and pleasant temperatures are nice, but active geology could make or break a planet’s habitability.

100 million years ago 50 million years ago Earth today Africa grabs Sinai India still fl oats free

Earth’s crust is split into nine giant plates and a bunch of smaller ones, some of which are labeled above. These plates move at diff erent speeds, ranging from about 2 to 15 centimeters per year. Some plates are crashing together to form mountain ranges, others are spreading apart, and some are sliding past each other. Generally, the movement is away from the Mid-Atlantic Ridge — which makes sense, given the plates’ trajectory over time (below).

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alteration, the plates could eventually lock up like an engine without lubricant.

“If we’ve learned anything from our planet,” says geo-dynamicist Craig O’Neill (Macquarie University, Australia), “it’s that both internal heat and water should be essential ingredients on other planets with plate tectonics as well.”

Although Mercury, Venus, the Moon, and Mars have experienced volcanism, none held onto their original inventory of liquid water. Venus’s extraordinarily dry, hellish fate was probably sealed by its ponderous rotation and proximity to the Sun. Even if Venus has a convecting liquid core, the planet’s 243-day spin rate is simply too slow to generate a magnetic dynamo. Without an active magnetic dynamo to protect Venus from the ravages of the solar wind, it lost most of its water vapor within a few hundred million years of its formation. And without liquid water to lubricate plate tectonics, Venus has lost most of its internal heat through episodic overturning of its crust.

“Episodic overturning is like subduction on steroids,” says O’Neill. “It’s like a massive subduction event that happens all at once and is all over and done within a few tens of millions of years.” The lesson from Venus is that many terrestrial planets and moons are likely to be in a temporary “stagnant lid” phase, akin to a steaming, some-times roiling pot of soup locked under an immobile lid.

Mars, in contrast, is so small and cold that its tectonics qualifi es as a permanent stagnant lid. Over the last few billion years most of its heat has just slowly conducted through its upper mantle and crust, called the lithosphere.

Without plate tectonics, it’s unlikely that Earth would have its current continent-ocean crustal dichotomy. This dichotomy arose because ocean crust (made mostly of vol-canic basalt) is denser yet thinner than continental crust (made primarily of granite). But ultimately, this dichot-omy also wouldn’t exist without water: to create future

subduction zones, convective stresses have to be able to rupture the lithosphere. Earth probably would not have subduction zones if its crust had not been hydrated in sea-water (and therefore weakened) over millions of years.

Without water, it would also be diffi cult to generate granite, the continental building block. Water lowers basalt’s melting point, and as a result, granite’s key min-eral components can diff erentiate. Earth is currently mak-ing continents as fast as it’s losing them, says geophysicist Norman Sleep (Stanford University). But when plate tec-tonics begins to slow, so will the formation of continents.

Getting Plate Tectonics GoingMost geologists credit this unique crustal dichotomy of oceans and continents with making Earth so wonderfully diverse and habitable. But there’s still much controversy over exactly when and how the geologic processes that resulted in this crucial dichotomy actually began. Did plate tectonics start soon after Earth’s formation, or much later?

Geologist Robert Stern (University of Texas at Dallas) favors a very late start for plate tectonics, perhaps only 1 bil-lion years ago. Relying on geologic evidence from ancient, exposed layers of rock, he says most rock associations for modern-style plate tectonics do not appear until the Neo-proterozoic Era, roughly 1 billion to 540 million years ago.

In contrast, geologists such as Mark Harrison (Univer-sity of California, Los Angeles) adhere to the view that plate tectonics started perhaps as early as 100 million years after Earth’s formation. Harrison bases his evidence on zirco-nium silicate minerals (zircons) from the Jack Hills of West-ern Australia. Harrison says that these zircons’ existence shows that Earth had continents and lots of liquid surface

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Earth recycles its crust via plate tectonics. Material for new crust wells up between two spreading plates, while old sediment melts when one plate dives under another in subduction zones.



water within the fi rst 500 million years of its formation. There’s also disagreement about just how much of a

factor a planet’s mass plays in the onset of plate tectonics. With the exception of planetary bodies such as Jupiter’s moon Io (which are tidally heated), planets need to be massive enough to sustain the high internal temperatures that drive mantle convection and plate tectonics. Geolo-gists are still vigorously debating what that minimum mass is. A rough upper limit is 10 Earth masses, because above that planets are prone to turn into Uranus-size giants. But ultimately, sustained plate tectonics may depend on contingencies, such as a moon-forming impact or maybe even microbial life that maintains surface water.

O’Neill actually doesn’t expect there to be a required minimum mass for the onset of plate tectonics. Computer simulations by his team suggest that an Earth-like mass doesn’t always translate into tectonic activity. It’s the interaction between driving and resisting strength in the lithosphere that’s critical, he says. The amount of radio-active isotopes in planetary interiors is also key, because these are the nuclear powerhouses for mantle convection. Regardless of a planet’s mass, a weak lid coupled with strong buoyant and thermal forces can mobilize the lid and lead to something like plate tectonics.

Until we fi gure out the cause and onset of global plate tectonics, it will be diffi cult to know whether it’s rare or commonplace on rocky planets. Still, most geologists are sanguine about prospects for exoplanet tectonics, based on their optimism in what Stern terms “theoretical uni-formitarianism,” which in this case refl ects the assertion of the universality of plate tectonics across the galaxy. But Stern cautions that a rocky Earth-like exoplanet won’t necessarily have active geology.

“If you ask us whether a planet around Alpha Centauri has plate tectonics, we’ll give an opinion,” he says. “But it won’t be an informed opinion, because we don’t really understand plate tectonics on our own world.”

Planetary ThermostatBased on our experience on Earth, planetary scientist James Kasting (Penn State University) says plate tectonics helps maintain a stable planetary thermostat by removing carbon dioxide. Wherever fresh crust is created, wind and water erode it. Dissolved calcium ions from the rocks then suck CO2 into the sedimentary cycle by reacting with CO2 in the air to form limestones.

Signifi cant amounts of CO2 also turn into compounds such as carbonate, which are then deposited into rocks and locked up underground. Another large portion of CO2 is dissolved in the ocean, which makes its way down into subduction zones and then into the mantle. Without such processes, carbon dioxide would simply build up to the point where Earth would experience a runaway green-house eff ect similar to Venus.

Therefore, says O’Neill, plate tectonics plays a crucial role in whether a planet could spawn complex life. “From

Radar mapping by ground- and space-based instruments reveals the two hemispheres of Venus’s surface, centered at longitude 0°° (left) and 180° (right). The maps are color-coded for elevation. No evidence has ever been detected for growing mountain ranges or spreading zones associated with plate tectonics.

NASA / JPL / USGS

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an astronomical point of view,” he says, “the habitable zone is a very nebulous concept. A planet’s distance from its star is important, but the primary concept in creating a habitable planet is atmospheric composition, where stellar energy and atmospheric composition provide surface tem-peratures and pressures that allow for liquid water.”

Having a suffi ciently massive super-Earth with liquid water in a star’s habitable zone does not mean that plate tectonics is a given. Stern gives the chances of a rocky exoplanet having plate tectonics as on the order of 20%. His estimate stems from the simple fact that only one of the inner solar system’s fi ve silicate planets (if we include the Moon) currently has plate tectonics.

In many cases, Earth analogs could still be what O’Neill terms “frozen dead bowls” or “searing hellholes,” depending on variables involving interior heat production and the strength of the lithosphere. “The more heat you have, the faster tectonics goes,” says O’Neill. “But if the lithospheric plates are too strong relative to the driving internal mantle, the plates won’t move.”

Fostering EvolutionIn addition to controlling temperatures, plate tectonics has also played a pivotal role in biological evolution. “Plate tectonics creates opportunities for diff erent populations of a species to become geographically isolated,” says paleo- biologist Bruce Lieberman (University of Kansas). “With-out geographic isolation, speciation won’t happen. Without speciation, evolution grinds to a halt. You need to have a series of speciation events for intelligence to evolve.”

For example, the formation of the East African Rift System may have spurred speciation 20 million years ago.

East Africa changed from a relatively fl at rainforest to a plateau-laden, mountainous terrain of rift valleys, basin lakes, and grasslands. Early human ancestors would have had to forage farther for food, forcing their brains to adapt to new environmental stresses.

And as geologist Stephen Mojzsis (University of Colorado, Boulder) points out, Earth’s plethora of dry land gives intelligent life a leg up. Although the galaxy might be awash with Earth-mass water worlds dotted with little Hawaiis where creatures sun themselves, complex life on these planets will arguably never evolve into technological civilizations. “Without dry land,” he says, “evolving intel-ligence won’t have fi re. Without fi re you can’t work ores and metals to make electronics to study the stars.”

Earth is the only known planet with this extant mix of oceans and continents. Although life may have diversi-fi ed in island niches, it’s possible that primate-to-hominid evolution might not have taken the same turn without continents and their transformations.

Astrobiologists won’t know for sure whether Earth’s biosphere is a relative anomaly until life-fi nder space tele-scopes survey exoplanet atmospheres and compositions. Spectroscopy from such missions may detect atmospheric

Laser altimetry mapped Mars’s topography at high resolution but yielded no evidence of plate tectonics. Valles Marineris (big cre-vasse in the left image) is probably a giant stress fracture formed as the planet cooled and the Tharsis region to the west rose.

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chemistries that are byproducts of microbial life in extrasolar small, warm ponds. But fi nding a world with full-blown plate tectonics capable of supporting complex life will require more than mere spectroscopy.

Research by Darren Williams (Penn State Erie, The Behrend College) and Eric Gaidos (University of Hawaii) highlights the promise of remotely sensing crustal dichoto-mies indicative of plate tectonics. Gaidos says that by track-ing changes in an exoplanet’s refl ected light, it might be possible during a single planetary rotation to see successive surfaces of land and ocean. A dark hemisphere might be the ocean, and a bright hemisphere, the land. By observing many rotations, he says, one could eliminate the possibility that clouds or weather are causing the eff ect.

At the very least, an 8- to 10-meter space telescope should be able to discriminate between an ocean planet with few clouds and a planet with either no oceans or widespread clouds. “Intermediate cases would be much harder to characterize,” says Gaidos.

A Grim FutureMeanwhile, what we learn from any exo-Earth analog will provide our own fragile species with a mirror of both our geotectonic past and future.

Within half a billion years or so, Earth’s cooling inte-rior will cause plate motions to become sluggish. Tecton-ics will begin grinding to a halt, and Earth will head into its own stagnant-lid phase.

“We will have no more active mountain building, a much lower rate of active volcanoes, and no additional crustal generation,” says O’Neill. “Anything above sea level will probably erode down to sea level. Eventually, the whole surface of Earth will just seize up.”

Sleep says harbingers of such sluggishness are already showing up in the Australian-Antarctic discordance, the sea fl oor between these two continents where a lot of subduction has occurred over the last several hundred mil-lion years. The area is now sucking up colder mantle that won’t readily melt to form granite. That means more water is heading into the mantle than is coming out through volcanism. In 700 million years, the oceans could simply disappear down a plethora of geotectonic rabbit warrens.

“Once you lose the water, you lose the plates,” says O’Neill. “Without lubrication, the plates will lock up, and plate motions will cease.” The end result could be a Frank Herbert-type Dune world — with limited groundwater and some surface water at the poles, but the rest of the planet a giant Sahara.

Given Earth’s abundant ocean water, Sleep bets we are more likely to drown than die of thirst. He suspects that once plate tectonics ends, the world’s oceans will bevel our stagnant continental crust into a state of terminal erosion, turning our home planet into a latter-day water world.

By that point, it may not matter anyway. In 500 million years, the brightening Sun is expected to disrupt photo-synthesis and usher in an era of atmospheric loss via photodissociation. Even if our distant progeny fi nd a way to somehow shield Earth from this predicted increase in solar luminosity, they will still have to contend with a planet whose innards have cooled beyond the bounds nec-essary to maintain plate tectonics. By then, it might just be easier to pack up, pass Pluto, and never look back. ✦

Science journalist Bruce Dorminey is author of Distant Wan-derers: The Search for Planets beyond the Solar System, and is a technology columnist for Forbes.com.

The North American Plate (left) and the Eurasian Plate (right) are splitting apart at this rift valley in Þingvellir National Park in western Iceland. The valley is essentially a short segment of the Mid-Atlantic Ridge sticking up above the ocean’s surface.

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Galactic Depth Perspective

Binoculars are the ideal tool for exploring the galaxy we call home.

Craig CrossenCraig Crossen

The largest single object in the sky is the Milky Way, which makes a full 360°° circuit around the heavens. But it isn’t a featureless, hazy band; it has bays, rifts, and star clouds that can be seen easily by the unaided eye and are often quite spectacular in binoculars — as long as you view them from a dark location on a clear, moonless night. These features, as well as the distribution of the brightest open clusters and nebulae along the Milky Way, refl ect our galaxy’s spiral structure in the neighborhood of the Sun.

We see the Milky Way in two dimensions, as though it were painted on the celestial sphere. But this view is misleading; objects at very diff erent distances often appear side by side or even superposed. That’s especially true in the constellations Sagittarius, Scorpius, and Ophiuchus, where several spiral arms lie between us and the center of the galaxy. This article is meant to give you a sense of depth perspective when you view this area with binoculars or your unaided eyes. It will be followed by two more articles describing the remainder of the Milky Way band and how its appearance refl ects our galaxy’s structure.

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OBSERVING THE MILKY WAY, PART I:

Photo by Babak Tafreshi




Vital StatisticsProfessional astronomers have nearly as much trouble as amateurs in discerning our galaxy’s structure; it’s diffi -cult to understand a forest when you’re surrounded by its trees. The broad outlines have been known or suspected for many decades, but the details are still controversial.

The Milky Way Galaxy seems to be an SBc spiral with fairly loosely wound, luminous spiral arms and a relatively small central bulge. The galaxy’s disk is probably not quite 100,000 light-years in diameter, and the Sun is between 25,000 and 29,000 light-years from the center. The spiral arms are less than 1,500 light-years thick when viewed edge on, but they’re embedded in a thick disk of more smoothly distributed stars some 3,000 to 4,000 light-years thick. The galaxy’s central bulge is something of a fl attened spheroid, with a polar diameter of roughly 8,000 light-years and an equatorial diameter around 10,000 light-years. In both the central bulge and the disk, star densities taper off gradually, so these dimensions cannot be specifi ed with precision.

The bulge is embedded in a weak central bar whose long axis is oriented between 10°° and 40° from our line of sight — making it diffi cult to detect. Some researchers think there are two superposed bars.

Our Milky Way Galaxy is well above average in terms of size, luminosity, and mass. For instance, our Local Gal-axy Group contains only one other galaxy of similar size (Messier 31), one that’s somewhat smaller (Messier 33), and several dozen that are much smaller.

The Milky Way contains well over 100 billion stars and probably well under a trillion — most of them consider-ably less massive and much less luminous than our Sun. Its total luminosity is at least 15 billion Suns, correspond-ing to an integrated absolute magnitude of –20.5.

Although stars account for almost all of our galaxy’s light, they make up only a fraction of its mass. A roughly comparable mass exists in the form of interstellar gas (mostly hydrogen and helium) and “dust” (microscopic particles). Dust accounts for less than 1% of the mass, but it has a disproportionate eff ect on our galaxy’s appear-ance and evolution because it blocks visible light, whereas hydrogen and helium are transparent at most wavelengths.

The Galactic CenterAstronomers have long suspected that the center of our galaxy lies near the junction of the constellations Sagit-tarius, Scorpius, and Ophiuchus. That’s both because this is the brightest and broadest part of the Milky Way band and because of the distribution of globular clusters. Of the 29 Messier globulars, seven are in Sagittarius, three in Scorpius, and six in Ophiuchus, compared to just one (M79 in Lepus) in or near the winter Milky Way.

The suspicion was confi rmed when radio observations detected a strong source at right ascension 17h 45.7m, declination –29° 00′, a visually unremarkable spot about 5° west-northwest of Gamma ( γ) Sagittarii, the western-

This image of NGC 4565 illustrates why it’s diffi cult to discern the Milky Way’s structure. We see both galaxies edge-on, with all their spiral arms superposed. Moreover, most of our galaxy is blocked from view by the dust that clogs its central plane.

Like the Milky Way, Messier 83 is an SBc spiral. But even with the luxury of observing it from “above,” it’s not easy to discern M83’s structure. How many spiral arms do you count? Two? Three? Five? Eight?

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most star in the Teapot asterism. Several lines of evidence indicate that these radio emissions come from an accre-tion disk spiraling around a supermassive black hole at the galaxy’s center.

The galactic nucleus — the area around the center — can be studied only at radio, microwave, and infrared wavelengths because the dust of the galaxy’s interior spiral arms, and the dense dust around the nucleus itself, blocks virtually all radiation at shorter wavelengths. Vis-ible light from the nucleus is obscured roughly 30 magni-tudes —a factor of one trillion — by intervening matter.

The nucleus is something like an extreme globular cluster, crowding more than 100 million stars into a sphere some 150 light-years in radius. (By contrast, there are only about 50,000 stars within 150 light-years of the Sun.) Deep inside the nucleus are three compact open clusters of rapidly evolving giant and supergiant stars mingled with dense gas and dust.

The Central BulgeDespite the heavy dust clouds in the central regions of our galaxy, we can see four layers of galactic structure when we look toward Sagittarius and Scorpius.

The Great Sagittarius Star Cloud is the innermost galactic structure that can be observed in visible wave-lengths and the most distant Milky Way structure that can be seen with the unaided eye. It stretches several degrees north from Gamma and Delta (δ) Sagittarii and is a splendid sight in small binoculars — a bright glow with multitudes of momentarily resolved star-sparks. It is in fact a section of the Milky Way’s central bulge.

The central bulge is depleted of the gas and dust from which new stars form, so unlike the spiral arms it contains no bright, young, blue stars. Instead, its bright-est stars are K-type orange giants. So on color photos the Great Sagittarius Star Cloud has a yellowish tint.

Most of our galaxy’s bulge is hidden from our view by the dust of the inner spiral arms. If we could see the whole bulge, it would stretch from the Stinger of Scorpius to the Small Sagittarius Star Cloud (Messier 24) and reach

Akira Fujii’s masterful photograph shows the central Milky Way as it appears from mid-northern latitudes. The dotted line marks the galactic plane. The ellipse shows how big the central bulge would appear if there was no dust in the way, assuming that it’s an 8,000 × 10,000 light-year ellipsoid centered 27,000 light-years away.

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The Sagittarius-Carina Arm of our galaxy is studded with active star-forming regions. One of the brightest is Messier 16, shown here in false color with oxygen, hydrogen, and sulfur represented by blue, green, and red, respectively.

more than halfway to Antares, as shown on the preced-ing page. The Great Sagittarius Star Cloud is visible only because of a rather large window through the interstellar dust of the galactic interior.

Several other similar windows allow us to see relatively long distances across our galaxy’s spiral disk. Another window through which we glimpse a segment of the galaxy’s central bulge is in the direction of the foreground open cluster Messier 7 in the Tail of Scorpius. On color photos the little star cloud around M7 has the same yellowish tone as the Great Sagittarius Star Cloud to its north. Thus we see M7, roughly 1,000 light-years away, superposed on the much more distant galactic bulge.

The Norma ArmAnother window through the interstellar dust of the galactic interior gives us a view of the second most dis-tant galactic structure visible in Sagittarius: the Small Sagittarius Star Cloud, also known as Messier 24. It’s a roughly rectangular glow stretching northeast to south-west, measuring about 2°° × ¾°, and located 2° north-northeast of Mu (μ) Sagittarii. In binoculars it’s not as bright as the Great Sagittarius Star Cloud, but it’s more richly sprinkled with 7th- to 10th-magnitude stars. M24’s estimated distance of 10,000 to 16,000 light-years implies that it’s a stretch of one of the deep interior spiral features of our galaxy. Its binocular appearance confi rms this, because spiral arms have many highly luminous super-giants that should be easily resolvable in small instru-ments even at M24’s distance.

M24 is probably part of the Norma Arm, the second spiral arm in from our own Orion-Cygnus Arm. Some researchers call this the Scutum-Centaurus Arm and use the term Norma Arm for a smaller arm that lies closer to the galactic center. This is the terminology adopted in the galaxy diagram on the foldout Milky Way map in the center of this magazine.

The bright Norma Star Cloud in the far southern Milky Way and the Scutum Star Cloud north of Sagittar-ius probably also lie in the Norma Arm. We will discuss them in future articles.

The Sagittarius-Carina ArmMoving outward from the Norma Arm toward the Sun, the next spiral feature is the Sagittarius-Carina Arm — so named because many major bright emission nebulae and open clusters are distributed along it from Sagittarius to Carina. From northeast to southwest these include M16 (the Star Queen or Eagle Nebula) in Serpens; the emission nebulae M17 (Swan), M20 (Trifi d), and M8 (Lagoon) in Sagittarius; the open clusters M21 in Sagit-tarius and NGC 6231 in Scorpius; the open cluster and emission nebula NGC 6193 and 6188 in Ara; the open cluster NGC 4755 (Jewel Box) in Crux; and the giant emission nebula NGC 3372, also known as the Eta Cari-nae Nebula. All of the emission nebulae contain embed-ded clusters and/or associations of young stars, though in some cases these stars are heavily obscured by dust.

Although it’s rather far south for observers in the northern United States and Europe, NGC 6231 in the Tail of Scorpius, a major tracer of the Sagittarius-Carina Arm, is well worth viewing in binoculars. It’s a special cluster, one of the richest concentrations of extremely hot and luminous O-type giants and supergiants known in our galaxy. An outlying member of the cluster is the 4.8-mag-nitude star Zeta1 (ζ1) Scorpii, ½° to its south. Zeta1 is a B1.5 Ia+ extreme supergiant with an absolute magnitude around –8.8 (a luminosity of almost 300,000 Suns).

Centered about 1° north-northeast of NGC 6231 is a rich binocular fi eld of 6th- to 9th-magnitude stars that is cata-logued as the open cluster Collinder 316 or Trumpler 24: it’s in fact the richest outlying part of Scorpius OB1, the vast stellar association of which NGC 6231 is the core. This area is also discussed in Binocular Highlights on page 40.

The Sagittarius-Carina Arm clusters and nebulae in Sagittarius and Scorpius are between 4,500 and 7,000 light-years distant, suggesting that in this direction the arm is centered about 5,500 light-years from us. Further northeast along the arm, M16 in Serpens is somewhat more distant, about 6,500 light-years. Here the Sagit-tarius-Carina Arm begins its arc in toward the galactic interior. The arm’s incurving edge is at the Scutum Star Cloud, where the Sagittarius-Carina and Norma arms may intersect. On the opposite, southwestern end of the Sagittarius-Carina Arm, the Eta Carinae complex is about

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The region around Antares is where the bright stars of the Scorpius-Centaurus Association overlap the dust clouds of the Great Rift. The stars illuminate the clouds and also cause them to fl uoresce, yielding a riot of color in deep photographs. Note the globular cluster Mess-ier 4 and the contrast between the red supergiant Antares and the blue star Sigma (σ) Scorpii.

8,000 light-years away. But other Sagittarius-Carina Arm associations have been identifi ed beyond it, because here the arm is beginning to curve out to the galactic exterior and we have a long view down its outcurving length.

The Orion-Cygnus ArmThe fourth feature of galactic structure visible toward Sagittarius is of course our own Orion-Cygnus Arm. Its inner edge is marked by the Great Rift chain of dust clouds from Deneb on the northeast to Alpha Centauri on the southwest. The Great Rift will be described in more detail in the next installment of this article.

The inner edge of the Orion-Cygnus Arm is also traced by the Scorpius-Centaurus Association, which includes the majority of the bright stars from Scorpius on the north-east, through Lupus and Centaurus, to Crux on the south-west. This association is centered about 550 light-years away in a direction between Alpha (α) Lupi and Zeta Centauri, and is highly elongated, being 700 light-years long, 250 light-years “high” (perpendicular to the galactic plane), and 400 light-years deep along our line of sight. It’s slightly nearer than the Great Rift chain of dust clouds, though Antares and a couple of other stars in the Head and Heart of Scorpius are just within the nearest fringes of Great Rift dust. Except for the M-type red supergiant Antares, all the bright stars of the Scorpius-Centaurus Association are blue B0, B1, and B2 main-sequence and giant stars. In binocu-lars the color contrast between ruddy-orange Antares and

the silver-blue Sigma (σ) and Tau (τ) Scorpii to its west-northwest and southeast is absolutely stunning. All three stars fi t in the same binocular fi eld of view.

Binoculars also show the bright (5.7-magnitude) globu-lar cluster M4 just 1.3° west of Antares. In 10×50 glasses, M4 appears as a large hazy patch (June issue, page 45). It’s one of the two or three nearest globulars to us, roughly 7,200 light-years away. This is about the same distance as the Sagittarius-Carina Arm, but globular clusters are far too old to be true spiral arm tracers. Spiral arms are thought to change fairly rapidly, perhaps even disappear-ing and reforming over billion-year time frames. Most of the Milky Way’s globular clusters, by contrast, seem to be nearly as old as the galaxy itself.

Moreover, M4 is a good way off the Sagittarius-Carina Arm, about 16° northwest of its core. So observers in M4 would have an excellent view “down” into the Sagittarius-Carina Arm. And because M4 is well outside the dust clouds that lie along the center of the Milky Way, any observers in the cluster would have a far better view than we do of the galaxy’s central bulge.

In the next two articles of this series we will visit our galaxy’s cardinal points to further our sense of depth per-spective on our place in the Milky Way Galaxy. ✦

Craig Crossen is a professional editor living in Vienna, Austria. He is coauthor with Gerald Rhemann of the book Sky Vistas: Astronomy for Binoculars and Richest-Field Telescopes.

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Telescope Tips

I ain’t afraid of no ghosts, but I am afraid of the fi lmy, non-ectoplasmic stuff that materializes on my telescope every clear night: dew. I’ve been battling the wet stuff for more than 30 years and these days I am usually victori-ous, but it hasn’t always been that way.

I got an education about dew shortly after I bought my 8-inch Schmidt-Cassegrain telescope in 1976. At fi rst, I was in amateur astronomy heaven, seeing more of the universe than I ever had with my homemade Newto-nian refl ector. But then the stars in the eyepiece began developing nebulous halos. I knew there wasn’t nebulos-ity around the stars of M37. Was my new scope broken? A look at the big corrector lens on the front of its tube revealed the problem: it was sopping wet with dew and my stargazing was done for the night.

Know Your EnemyBefore you can bust dew, you need to know your enemy. Where does it come from? Why does it fall? Actually, dew is nothing more than moisture condensing out of the air. It doesn’t fall, but rather forms on an exposed surface when that surface becomes colder than the dew-point temperature, which depends on the humidity. The higher the humidity, the closer the dew point is to the air

BustingDew can form suddenly and almost without warning. Here’s how to stop it from ruining a nice night under the stars.

ROD MOLLISE

Dew has long been the bane of observers, but it’s especially problematic for popular Schmidt-Cassegrain telescopes such as the author’s 8-inch Celestron pictured here, which has a thin cor-rector plate that is highly susceptible to dew formation.

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temperature. At 100% humidity, the dew point is equal to the air temperature and dew will begin to form immedi-ately. As humidity gets lower, the dew point also becomes increasingly lower than the air temperature.

A telescope’s lens or mirror becomes colder than the surrounding air because of radiative cooling. Under a clear night sky, heat is literally sucked out of the optics. The telescope radiates its heat away into space. After minutes or hours, the glass cools to below the dew-point temperature and moisture begins to form.

How much of a problem is dew in astronomy? That depends on your location and telescope type. If you live in the desert, there’s usually not much to worry about. The air is so dry and the dew point is so low that no matter how much the telescope cools, the optics will rarely fog up. The fi rst time I attended the Texas Star Party, I was amazed to fi nd that my dew troubles had evaporated. Nothing had the slightest bit of moisture on it by dawn. Unfortunately, that’s not the way it is at my home in Ala-bama or in most other areas of the country.

A typical Newtonian telescope has its main mirror at the bottom of a long tube that usually shields it from all but a small patch of sky. Its heat is radiated away more slowly than if the mirror was exposed to a full 180°° view of heat-sucking space. Observers with Newtonian telescopes can be troubled by moisture on the telescope’s secondary mirror and eyepieces, but dew is a lesser con-sideration for them than for owners of refractors, which have their optics exposed at the top of the tube. Even more prone to dew are Schmidt-Cassegrain, Maksutov, and other designs with large corrector lenses at the front of the tube. Schmidt-Cassegrains’ thin correctors dew up fastest, but even Maksutovs, whose thicker lenses retain heat longer, are not immune.

The Passive ApproachThe simplest way to keep dew off a telescope’s optics is to use a dew shield, which emulates the long tube of a Newtonian. You don’t have to put a 4-foot tube on the end of your Schmidt-Cassegrain, though, just an exten-sion long enough to block the optics’ direct line of sight to everything but the area of the sky where the telescope is pointed. How long does this dew shield need to be? A good rule of thumb is at least 1½ times longer than the diameter of the telescope’s optics. A good dew shield for an 8-inch scope will be 12 inches long. Even if your refrac-tor, like most, came with a dew shield, it may be too short. If it is, then you should consider replacing it or supple-menting it with a longer one.

Where do you get a dew shield? Most telescope dealers sell them in a variety of sizes for refractors and Schmidt- and Maksutov-Cassegrain telescopes. They come in two types — rigid cylinders made of plastic or aluminum, and

fl exible plastic sheets that are rolled into a cylinder and held together with Velcro during use. Rigid dew shields are sturdier and less prone to droop into a telescope’s light path, but they are also less convenient to pack for storage or transport. Commercial dew shields, regardless of type, are relatively expensive, especially considering how easy they are to make.

The material for a homemade dew shield can be almost anything that can be formed into a cylinder and slipped over the end of the telescope tube. I’ve seen eff ec-

An exposed Schmidt-Cassegrain corrector plate (above) quickly radiates its heat into space when pointed at the night sky, causing its temperature to drop below the dew point with predictably disastrous results. But attaching a simple dew shield (two com-mercial models are shown below) to the front of the telescope tube will slow the radiative heat loss and can sometimes be enough to ward off dew for an entire night.



Telescope Tips

tive disposable ones made of black poster paper. What I prefer, however, is an insulating material that not only blocks some of the sky but also helps keep the optics warm. Readily available materials that I’ve used in the past include foam mats sold in outdoor stores as ground pads for sleeping bags and aluminized Sun refl ectors made for car windshields.

Once you have the material, the rest is easy. Use self-adhesive Velcro to hold the dew shield in the shape of a tube when you’re ready to put it on the scope, and, if

necessary, you can blacken the interior of the shield with fl at-black paint to prevent refl ections. That’s all there is to it. If the material isn’t rigid enough and tends to droop into the telescope’s light path, it may be necessary to strengthen the dew shield’s end, maybe with some layers of duct tape wrapped around its circumference.

Some fi nderscopes come with dew shields, but almost all are too short. As with the main telescope, almost any material that can be formed into a tube can work as a fi nder dew shield. A small container with its bottom cut off and the interior painted black works well. I’ve used everything from frozen orange juice cans to fi sh food containers. How about the popular Telrad refl ex fi nders? Their beam-splitter viewing windows are especially prone to dewing up. There are inexpensive commercial solu-tions, but it’s easy to make a cardboard or plastic cover to protect the exposed glass.

How about eyepieces? You can’t put a dew shield on them. I often just replace the eyepiece’s lens cap when I am not looking through it. The natural heat radiating from my eyeball keeps the eyepiece clear of dew while I’m observing, but eventually I forget to cap the eyepiece and dew forms on its outermost lens. The solution is to take active measures.

The Active ApproachIn many areas, a dew shield alone won’t keep optics clear all night. I supplement my dew shield with active dew-busting tools that warm the optics until they are above the dew-point temperature. Gentle heat is the key. You don’t want to blast your Schmidt-Cassegrain corrector

Dew strips and heat guns are best used intermittently to keep them from drain-ing batteries. Advanced dew-strip controllers can automatically cycle the power to maintain the optics at a set temperature above that of the ambient air.

When a dew shield alone isn’t enough to keep the temperature of telescope optics warmer than the dew point, you can actively apply gentle heat to the optics. One of the best ways to do this for refractors and Schmidt-Cassegrains is with a fl exible heating strip (left) wrapped around the telescope tube. Another solution is a battery-powered heat gun such as the one used by the author (right).



with a 1,500-watt hair dryer. That will most assuredly remove dew, but it may also distort the fi gure of the cor-rector, causing blurred images until it cools off , and when it does, dew will begin to form again.

One of the most popular active dew busters sold dur-ing the past 30 years is a dew-removal tool known to ama-teur astronomers and astronomy vendors as a dew zapper. These small heat guns are also sold as window defrosters in auto-parts stores and as battery-powered hair dryers in sporting-goods stores. Not that these 12-volt devices would do very well as hair dryers (they don’t get hot enough), but their gentle heat is perfect for removing dew from telescope optics.

To use one of these dew zappers, aim it at a scope’s lens, holding it about 12 inches from the surface. Keep it moving as you zap, and continue heating for a while after the last of the moisture disappears. A little extra heat will extend the time the lens remains dew free. A zapper works just as well on fi nders and eyepieces, and if you observe from a relatively dry area it may be all you need in addition to a dew shield.

Dew zappers work, but unless your humidity is low, you will likely have to dry your optics frequently during the course of an evening. And this gets old in a hurry. Inevitably, just as I am about to make the observation of a lifetime, it’s time to zap the corrector again. What’s needed is a way to apply a small amount of constant heat, just enough to warm the optics above the dew point. A heating element wrapped around a telescope’s lens, will do the job.

Flexible Dew HeatersLike most great innovations, it’s unclear who invented dew heaters for telescopes. The rising popularity of Schmidt-Cassegrain telescopes in the 1970s made the

time ripe for the idea, and it seems to have sprung from many sources. Amateurs and retailers began making simple heater strips, taking nichrome wire (the kind used in electric toasters) and sewing it into a cloth band that can be wrapped around the end of a Schmidt-Cassegrain or refractor. Connect the strip to a battery and dew was gone and stayed gone.

The initial designs weren’t perfect, however. When you plugged a heater strip into a battery, the constant current drain quickly exhausted even large batteries. The optics also got hotter than necessary, leading to distortion of the lens and the formation of hot air currents that ruined images. Canadian amateur astronomer Jim Kendrick took the dew heater to the next level, developing a modular system. His big contribution was adding an electronic controller that regulated the on-off cycle of power fl owing to the heater. This kept the optics from overheating and a battery from dying a premature death.

There was still room for improvement. It was hard to know how to set the controller under varying conditions. If it felt like dew would be heavy, you naturally cranked up the controller, often draining the battery before the evening was over. But if you didn’t turn it up enough, dew formed and you were done anyway.

In the 1990s, Ron Keating of Louisiana, which is as famous for dew as it is for gumbo, was showing off his DewBuster system that lets the controller decide when to apply power to the heaters. A temperature sensor set the controller to keep the heater strips just 5°°F (3°C) warmer than the ambient air. On most nights this prevented dew

Finders also suff er when dew starts to form, and red-dot and refl ex fi nders, such as the Telrad pictured here, are particularly prone to dewing. Solutions range from custom-made heaters to dew shields that fl ip out of the way when the fi nder is in use.

Canadian ama-teur Jim Kendrick developed some of the fi rst commer-cial dew-removal systems. He was the fi rst to intro-duce a controller that cycled power on and off to dew heaters, preventing excessive battery drain and unneces-sary overheating of telescope optics. His company, Ken-drick Astro Instru-ments, remains a leader in the fi eld.



Telescope Tips

from forming. It was a substantial improvement, and several manufacturers of dew-removal heaters, including Kendrick, now off er temperature-controlled systems.

You can heat just about anything with a Kendrick or a DewBuster. Strips are readily available for Schmidt cor-rectors and refractor objectives in sizes up to 16 inches. There are also heater strips for 1¼- and 2-inch eyepieces, fi nderscopes (including Telrads), and even laptop com-puter screens. Got a Newtonian with a secondary mirror

Top: As explained in the accompanying text, the placement of dew heaters is important to their success. The author recommends wrapping heaters around the telescope tube just behind a refractor’s objective or a Schmidt-Cassegrain’s corrector rather than around the cell holding the optics. Above: Dew is a problem for more than just telescope optics. A simple cardboard enclosure is an eff ective way to keep computers and other electronic equipment dew free.

that collects dew? You’re not left out. Dew heaters are available for Newtonian secondaries too.

Dew heaters are a simple and elegant idea, but there are a few things to consider if they are to be eff ective. The fi rst is battery capacity. Most manufacturers give an estimate of the current consumption of their heaters. For example, when it’s on, a heater strip for an 8-inch correc-tor might draw 1 ampere of current. Although the heater isn’t likely to be on all the time, for the sake of determin-ing how large a battery you need it’s best to assume it will be. If a typical observing session lasts 8 hours, choose a battery rated for at least 8 ampere hours of output. Once you add in heaters for eyepieces and fi nders, a 17-ampere-hour battery is just about right.

Second is timing. Power up the heaters no later than sunset, since that’s when the telescope begins to cool rapidly. I uncap my corrector or objective and turn on the dew controller a half hour before the Sun slips below the horizon to allow adequate time for the optics to warm up. The goal is to prevent dew from forming in the fi rst place. It is much easier to keep dew off a lens than it is to remove it. I normally set my DewBuster’s controller to 5° above ambient, but increase it to 10° when I expect the dew to be heavy.

Third is placement. With a Schmidt-Cassegrain, it’s important to wrap the heater strip for the corrector around the telescope tube just behind the big metal lens cell for the corrector. If the strip goes over the cell, too much of its heat will go to warming the metal, not the lens. Positioned behind the cell, the strip’s heat will rise inside the tube and warm the corrector effi ciently. The same thing goes for a refractor: place the strip behind the objective cell. Placement of the heater strip on eyepieces and fi nders is not as critical; just wrap a strip around the eyepiece and the objective end of the fi nder. Lastly, heat-ers always work best in conjunction with a dew shield. Indeed, they will often fail to keep dew away for an entire night just by themselves.

One recent humid evening, I was happy to help a novice astronomer learn to bust dew. He hadn’t thought a dew shield or heaters were important since they weren’t in the box with his new Schmidt-Cassegrain telescope. If I hadn’t loaned him my dew zapper gun, he wouldn’t have seen anything — his corrector began to dew up right at sunset. I used to tell novices that dew-removal gear is just as important as eyepieces, but I was wrong. It is more important. You can always see something with the simplest, cheapest eyepiece , but unless you are prepared to deal with dew, you may not see a thing. ✦

Contributing editor, noted book author, and long-time ama-teur astronomer Rod Mollise most often battles dew in the observing fi elds around his home in Mobile, Alabama. His article on deep-sky observing with video cameras appears in last February’s issue, page 70.



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Fred SchaafOBSERVING Northern Hemisphere’s Sky

Fred Schaaf welcomes your comments at [email protected].

Tales of the Northern CrownThis small constellation is full of drama, both real and mythological.


Last month in this column, we began a tour and appraisal of the lovely constellation Corona Borealis, the Northern Crown. This month we’ll consider two of the constellation’s remarkable double stars, its amazing recurrent nova, and two of its most beautiful legends.

Double-star wonders. The members of the Eta (η) Coro-nae Borealis system have a tight 42-year orbit and so have completed almost 4½ revolutions since their discovery by Friedrich Georg Wilhelm von Struve in 1826. The two stars, near twins of our Sun, lie only 59 light-years from us. Their apparent magnitudes are 5.6 and 6.1 but their small separa-tion — currently 0.7″ — calls for a night of very steady seeing and a telescope with at least 8 inches of aperture.

Zeta (ζ) Coronae Borealis, up in the northern part of the constellation, is a pair of 5.0- and 6.0-magnitude stars that are an easy 6″ apart. Zeta has been rated one of the six most beautiful colored doubles for small telescopes on a list com-

piled by Michel Duval in the Observer’s Handbook published by the Royal Astronomical Society of Canada. What colors do you see in Zeta?

Watching for the blaze. Recurrent novae are systems in which material falling from a star onto an unusually mas-sive white dwarf companion sets off tremendous outbursts of brightness at intervals of a few to many decades. The brightest of all these objects is located only about 1°° south of Epsilon (ε) Coronae Borealis. The star’s name is T Coronae Borealis, but it is also known as the Blaze Star.

T CrB usually shines at 10th magnitude. But on May 12, 1866, T fl amed up to a magnitude of 2.0, slightly brighter than Alpha (α) CrB. Then the Blaze Star began to fade, at the rapid rate of about ½ magnitude a day, eventually returning to its original dimness. But on February 9, 1946, the Blaze Star burst forth again, this time to a maximum of 3.0. Do the outbursts occur with a regular period, in which case another will take place in 2026? It’s possible that one of these times so much material will fall on the white dwarf that T will blow up as a Type Ia supernova and shine as bright as a crescent Moon even though it’s more than 2,000 light-years distant.

Two lovely myths. In Greek mythology, the semicircle of Corona Borealis is the crown of Ariadne, daughter of King Minos of Crete. She helped the hero Theseus escape from the winding Labyrinth in which Theseus killed the monstrous Minotaur, who was part man, part bull. Then Ariadne ran off with Theseus, who had pledged his love to her. But Theseus abandoned Ariadne on a lonely island. Fortunately, the god Dionysius found the sad woman, courted her, and made her his queen. After a happy life, when Ariadne died, Dionysius placed the crown he had given her up in the heavens — where we see it shine in honor of her as Corona Borealis.

Another story — this one from the Shawnee Indians — tells how the warrior Algon spirited away the loveliest maiden in a circle of heavenly sisters who had come down to Earth to dance. The other sisters fl ed back to the heavens, and the loveliest maiden fell in love with Algon and became his wife. But she also missed her sisters, and one day she returned to the sky with them in a silver basket.

The story has a happy ending: Algon was allowed to come to the heavens, where he became our star Arcturus. We see the dancing circle of sisters near him as Corona Borealis, but the circle is incomplete. So where is the loveliest sister? Is she joined with Algon in Arcturus? Or, just possibly, could she be the Blaze Star? ✦S&

T P

HO

TO A

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Friedrich Georg Wilhelm von Struve discovered that Eta Coronae Borealis is a double star with the great 9½-inch Dorpat Refractor, shown above.

NHS layout.indd 38 5/7/13 9:18 AM

MIDNIGHT S UNRISE ▶

Mercury

Venus

Mars

Jupiter

Saturn

◀ SUNSE T

Planet Visibility SHOWN FOR LATITUDE 40° NORTH AT MID-MONTH

Visible July 24 through August 16

Visible starting July 5

WSW

E

E

E

W

24

31

7

14

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S UN M O N T U E W E D T H U FR I S AT

Moon Phases

29

OBSERVING Sky at a Glance

EXACT FOR LATITUDE 40º NORTH.

Galaxy

Double star

Variable star

Open cluster

Diffuse nebula

Globular cluster

Planetary nebula

Using the Map

Go out within an hour of a time listed to the right. Turn the map around so the yellow label for the direction you’re facing is at the bottom. That’s the horizon. Above it are the constellations in front of you. The center of the map is overhead. Ignore the parts of the map above horizonsyou’re not facing.

JULY 2013 3 Dusk: An hour after sunset, binoculars or a wide-fi eld telescope may show that Venus, very low in the west-northwest, is on the edge of M44, the Beehive Cluster.

5 Earth is at aphelion, its farthest from the Sun for the year (3.3%% farther than it is at perihelion in January).

15 Evening: Spica is very close to the fi rst-quarter Moon as seen from the Americas. The Moon occults (covers) Spica in parts of Central and South America.

16 Evening: Saturn shines above the Moon, with Spica now to their right.

16, 17 Dawn: Jupiter and Mars have closed to just 2.2° apart, very low in the east-northeast an hour before sunrise. Binoculars or a telescope may show that the open star cluster Messier 35 is ½° above Mars.

21 Dusk: Look 1¼° lower left of Venus for much fainter Regulus very low in the west 45 minutes after sunset. Bring binoculars.

22 Dawn: Faint Mars glimmers ¾° upper left of bright Jupiter low in the east-northeast an hour before sunrise. Best in binoculars and small telescopes.

Dusk: Regulus is again very near Venus — this time 1¼° below the planet.

New July 8 3:14 a.m. EDT

Full July 22 2:16 p.m. EDT

First Qtr July 15 11:18 p.m. EDT

Last Qtr July 29 1:43 p.m. EDT

2h

23 h

20h

1

+60°

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E C L I P T I C

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( C A U D A )

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North Facing

MoonJuly 22

MoonJuly 19

Foldout July2013.indd 39 5/2/13 9:45 AM

–1

Starmagnitudes

0

1

2

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Gary SeronikBinocular Highlight

False Comet, Real BeautyOne of the very fi nest binocular fi elds in the entire sky is located in Scorpius, just north of the eastern bend in the constellation’s “fi sh hook.” There you’ll fi nd a trio of interesting sights that, when taken together, form a splendid splash of starlight known as the False Comet. The moment you train your binoculars on this ersatz comet, the illusion is shattered. But that doesn’t mean the view is any less splendid — quite the contrary.

The nucleus of the False Comet is a lovely star triangle consisting of the bright, wide, optical double Zeta (ζζ) Scorpii (magnitudes 3.6 and 4.8, separated by roughly 6½′) and a neighboring 5.8-magnitude star situated due south. Look closely at the Zeta pair. Can you make out any colors? To my eye, the brighter of the two has a lovely, honey-yellow tint, while its companion is a cool white.

Proceeding up the tail of the comet, we come to the pretty, compact open cluster NGC 6231. In my 10×30 image-stabilized binoculars, I can make out a tight quartet of 6th-magnitude stars enmeshed in a compact background haze of faint starlight. My 15×45s double the number of individual stars in the cluster, adding to its sparkly splendor.

A curving row of 6th- and 7th-magnitude stars trails north-northwest from NGC 6231 to the big open cluster Collinder 316, also known as Trumpler 24. Forming the broad end of the comet’s tail, Cr 316 is a sparse collection of eight fairly bright stars along with a smattering of fainter glints winking in and out of view in my 10×30s. I can also make out a second clump of stars near the cluster’s northeast edge, lending the comet’s tail an extra touch of luminance. ✦

To watch a video tutorial on how to use the big sky map on the left, hosted by S&T senior editor Alan MacRobert, visit SkyandTelescope.com/maptutorial.

Watch a SPECIAL VIDEO

6268

6231

Cr 316

6242

6281

6322 η

μ

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S C O R P I U S

When

Late May 2 a.m.*Early June 1 a.m.*Late June Midnight*Early July 11 p.m.*

Late July Dusk* Daylight-saving time.


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Saturn Moon

July 15


About the Image & Its PhotographerThis Milky Way panorama is a mosaic of almost 1,200 separate images taken by French astropho-tographer Serge Brunier and composited by his friend Frédéric Tapissier. Brunier shot most of the photos from Chile, but he completed the northern section in the French Alps and on a mountaintop in the Canary Islands, pictured at left.

The detail shown here is limited by the printingprocess; the original 800-gigapixel mosaic can easily fi ll a 12-foot-wide poster. You can zoom in to see any piece of it in more detail at sergebrunier.com/gallerie/pleinciel/index-eng.html.

M38M36

M37 Capella

Double Cluster

Andromeda Galaxy

Le

Cygnus OB7

Cepheus OB2

A U R I G A

C A S S I O P E I A

180° 150°

HyadesPleiades

Alpha Persei Cluster

Perseus OB3

120°


e Gentil 3

North America Nebula

Northern Coalsack

Cygnus Star Cloud

Great Rift

M11

M16M8

M17 M24

Altair

Deneb

Vega

LY R A

A Q U I L A

S

N O R T H E R N C R O S S

90°60°

30°

G o u l d ’ s B e l t

Jupiter in 2008

G°

150°

120°

90°

60°

30°

Perseus A

The drawing at right was made by Robert Hurt, artist and astronomer for the California Institute of Technology, and published by NASA. It represents the current best information about our Milky Way Galaxy’s structure. It’s based on recent studies with infrared and radio telescopes, which can penetrate the dust clouds that block most of our galaxy from view in visible light. The dust clouds lining the inner edge of our own Orion Spur form the Great Rift that stretches from Deneb on the left to Alpha Centauri on the right.

These dust clouds are actually composed almost entirely of hydrogen and helium, but those gases are transparent, so we don’t see them. The “dust” that blocks the light actually consists of tiny solid particles, more like soot or smoke than what we normally call dust.

Totally unseen is the huge halo of dark matter that envelops the entire galaxy. We know it’s there only because of its gravitational eff ects.

Like most spiral galaxies, the Milky Way is nearly fl at, except for a spheri-cal bulge near its center. It’s very diffi cult to discern our galaxy’s spiral struc-ture because we see it edge-on, with all the spiral arms superposed. For instance, the cluster M7, roughly 1,000 light-years distant, lies in front of the stars of the galaxy’s central bulge, more than 20,000 light-years distant.

Even when we can measure the distances to various features accurately, it is still very diffi cult to say how they link up into spiral arms. So the precise structure of our galaxy is still an open question.

The Spiral Galaxy That We Call Home


Sun

Scutum-Centaurus Arm

M7

62313532

25

6193 + 6188

Dark Horse

Scorpius OB1

Great Sagittarius Star Cloud

Norma Star Cloud

Alpha Centauri

Omega Centauri

Eta Carinae Nebula

SouthernPleiades

Large Mage

Small Magellanic Cloud

Coalsack

Jewel Box

Antares

S C O R P I U S

V E L AS O U T H E R N C R O S S

S A G I T T A R I U S

0° 330° 300°

Scorpius - Centaurus Association

alactic Longitude0°

330°

300°

270°

240°

210°180°°

Arm

Orion Spur

Sagittar

ius-

Carin

a A

rm

Galactic longitude is marked out at 30° inter-vals by tick marks along the galactic equator. Longitude 0° marks the position of the galactic center. When we look in that direction, toward Sagittarius and Scorpius, we see at least three spiral arms (including our own) superposed in front of the central bulge. This area is dis-cussed and charted in more detail in the article “Observing the Milky Way, Part I,” on page 24.

When we look toward galactic longitude 180°, between Auriga and Gemini, we’re looking directly away from the galactic center. That’s why the Milky Way appears so much

Galactic Longitude

dimmer and thinner in this direction. Because our Sun is located toward the inside of our own Orion Spur, our view in this direction includes many stars and a few star clusters within the Orion Spur, notably the Alpha Persei Cluster. But most of the clusters and nebulae in this area lie in the Perseus Arm, the next spiral arm out from our own. The brightest of these is the magnifi cent Double Cluster in Perseus.


516

M41

M47

M352264

M48

Rosette Nebula

Betelgeuse

M44

Procyon

M46

Sirius

Rigel

Great Orion Nebula

Monoceros OB2

Gemini OB1

Orion OB1

ellanic Cloud

Canopus

C A R I N A

P U P P I S

O R I O N

270°240°

210°

Canis Major Association

Galactic EquatorMonoceros OB1

Galactic Equator: the plane of our Milky Way Galaxy.

Gould’s Belt: Most nearby star clusters and nebulae, both bright and dark, lie near this line.

Stellar associations: large groups of young stars, usually types O and B, that all have a common origin. Most of the associations shown above have been adapted from Glenn LeDrew’s detailed Milky Way charts in The Backyard Astrono-mer’s Guide (Firefl y Books, 2010).

Dark nebulae: areas where the Milky Way is hidden from view by nearby dust clouds.

Star clouds: rich patches of spiral arms or the central bulge that are visible through windows in dust clouds.

90 Sherman StreetCambridge, MA 02140SkyandTelescope.com


OBSERVING Sun, Moon && Planets


July Planet PairingsVenus passes Regulus, and Jupiter pairs with Mars.

For all of July, bright Venus appears low in the west at dusk, and dim Mars glows low in the east-northeast at dawn. Both planets have exciting close conjunctions in the latter part of the month: Regulus drops down very close past Venus, and Jupiter fl oats up very close past Mars.

Saturn, meanwhile, is visible from dusk until the middle of the night. And at July’s end, Mercury peeks up very low in the east-northeast at dawn below Jupiter and Mars.

D U S KVenus sets only about 1½ hours after the Sun all summer for viewers at mid-northern latitudes. It stands only about 10° above the western horizon by the time it’s plainly visible a half hour after sundown. That’s so low that it’s diffi cult for telescopes to show that its 12″-wide disk is slightly gibbous. So the best time to observe Venus through a telescope is well before sunset, as described on page 51 of last month’s issue.

The biggest attraction for Venus-watchers this month is its close conjunc-

tion with 1st-magnitude Regulus. The star begins July 25° to Venus’s upper left, but closes the gap steadily. They pass just 1¼° apart on the American evenings of July 21st and 22nd. Venus shines at magnitude –3.9, 130 times brighter than Regulus at +1.4. Even so, Regulus should be visible to the naked eye if your sky isn’t too hazy. Binoculars and small rich-fi eld telescopes will show the pair beautifully.

E V E N I N G A N D N I G H TSaturn, near the boundary of Virgo and Libra, is several months past opposition but still well placed at nightfall almost halfway up the south or southwest sky. It fades just a trace during July, from magnitude +0.5 to +0.6. Saturn is station-ary in right ascension on July 9th, so it spends the entire month about midway between Spica and Alpha Librae.

Saturn is at eastern quadrature — 90° east of the Sun — on July 24th. So July and August are when the planet’s black shadow is especially wide on the magnifi cent rings, just off the globe’s

eastern edge. Observe Saturn through your scope early, before it sinks low.

Pluto, the brightest Kuiper Belt object, reaches opposition on July 2nd but still shines at only about magnitude 14.0. To detect and identify the far-fl ung world visually requires dark skies, a fairly large amateur telescope, and a detailed fi nder chart such as the one on page 52 of last month’s issue.

No bright planet is visible for several hours after Saturn sets. But Neptune rises before midnight (daylight-saving time), and Uranus rises 1½ hours after Neptune. They’re in Aquarius and Pisces respectively, high enough for good telescopic viewing at the onset of morning twilight. You can fi nd them with the maps at skypub.com/urnep.

D A W NMars begins July as a 1.5-magnitude object that’s only about 8° high in the east-northeast 30 minutes before sun-

Aldebaran

Pleiades

MoonJuly 3

MoonJuly 4

MoonJuly 5

Looking East

Dawn, July 3 – 51 hour before sunrise

10°

Dawn, July 5 – 630 minutes before sunrise

Aldebaran

Mars

Jupiter

MoonJuly 5

MoonJuly 6

Looking East-Northeast

ζ Tau

β Tau

Dusk, July 10 –1245 minutes after sunset

Regulus

Denebola

Venus

MoonJuly 10

MoonJuly 11

MoonJuly 12

Looking West

L E O

γ

Foldout July2013.indd 45 5/2/13 3:29 PM

Fred SchaafTo see what the sky looks like at any given time and date, go to SkyandTelescope.com/skychart.

Jupiter

Neptune

Uranus

Pluto

Saturn

Marchequinox Sept.

equinox

Decembersolstice

June solstice

Mars

Earth

SunMercuryVenus

ORBITS OF THE PL ANETSThe curved arrows show each planet’s movement during July. The outer planets don’t change position enough in a month to notice at this scale.

rise (if you’re near 40° north latitude). At that time and date Jupiter is just rising, 10° to Mars’s lower left. Even though Jupiter shines at magnitude –1.9, it’s so low as sunrise nears that you’ll need binoculars to see it.

On the American morning of July 6th, a lovely crescent Moon acts as a guide to fi nding Mars in binoculars just a few degrees to the Moon’s upper left. A telescope might show the star Zeta (ζ) Tauri between them. By this date, Jupiter may be high enough to see without opti-cal aid to their lower left.

Jupiter climbs closer to Mars each day until, on the morning of July 22nd — the same day Venus and Regulus are closely paired at nightfall — Jupiter and Mars are only 0.8° apart. They’ll fi t together in a low-magnifi cation telescopic fi eld that morning, though Mars will be a blurry speck less than 4″ wide compared to Jupiter’s 33″ globe.

By July’s end Mars is rising more than 2 hours before the Sun, and Jupiter is pulling up and away from Mars into much more obvious view. Or at least this is the perspective relative to sunrise. In

relation to the background stars, Mars is racing eastward into central Gemini, leaving much slower Jupiter behind in the Twins’ feet.

Mercury is in inferior conjunction with the Sun on July 9th, and it’s too dim and low in morning twilight to be visible until the last week of July. Then Mercury brightens rapidly, reaching almost zero magnitude by the time it comes to great-est elongation on July 30th. Mercury’s minimum separation below Mars is about 7° on July 28th.

E A R T H A N D M O O NEarth is at aphelion, its farthest from the Sun in space, around 11 a.m. EDT on July 5th. Its distance then is 94,509,959 miles, 1.7%% farther than average.

The Moon is a waning dawn sliver near Mars and Jupiter on July 6th (as described above) and a waxing dusk sliver rather far below Venus and Regu-lus on July 10th and 11th. Around fi rst quarter, the evening Moon shines very near Spica on July 15th and well below Saturn on July 16th. ✦

Dawn, July 2245 minutes before sunrise

Castor

PolluxMercury

Mars

Jupiter


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apart!

Dawn, July 311 hour before sunrise

Castor

PolluxMercury

Mars

Jupiter


G EM I N I

γ

Dusk, July 2245 minutes after sunset

RegulusJust11/4ºapart!

Denebola

Venus

Looking West

L E O

Foldout July2013.indd 46 5/2/13 3:29 PM

OBSERVING Planetary Almanac

Sun and Planets, July 2013

The table above gives each object’s right ascension and declination (equinox 2000.0) at 0h Universal Time on selected dates, and its elongation from the Sun in the morning (Mo) or evening (Ev) sky. Next are the visual magnitude and equatorial diameter. (Saturn’s ring extent is 2.27 times its equatorial diameter.) Last are the percentage of a planet’s disk illuminated by the Sun and the distance from Earth in astronomical units. (Based on the mean Earth–Sun distance, 1 a.u. is 149,597,871 kilometers, or 92,955,807 international miles.) For other dates, see SkyandTelescope.com/almanac.

Planet disks at left have south up, to match the view in many telescopes. Blue ticks indicate the pole currently tilted toward Earth.

Sun 1 6h 39.8m +23° 07′ — –26.8 31′ 28″ — 1.017

31 8h 40.7m +18° 19′ — –26.8 31′ 31″ — 1.015

Mercury 1 7h 33.7m +18° 30′ 13° Ev +3.2 11.5″ 7% 0.587

11 7h 10.2m +17° 34′ 5° Mo +5.4 11.7″ 1% 0.575

21 6h 55.6m +18° 41′ 16° Mo +2.1 9.9″ 13% 0.682

31 7h 18.0m +20° 26′ 20° Mo 0.0 7.5″ 41% 0.893

Venus 1 8h 26.1m +20° 52′ 25° Ev –3.8 11.1″ 90% 1.504

11 9h 15.6m +17° 39′ 27° Ev –3.9 11.5″ 88% 1.452

21 10h 02.8m +13° 39′ 30° Ev –3.9 11.9″ 86% 1.396

31 10h 48.1m +9° 06′ 32° Ev –3.9 12.5″ 83% 1.337

Mars 1 5h 21.7m +23° 32′ 18° Mo +1.5 3.8″ 99% 2.453

16 6h 06.4m +23° 58′ 22° Mo +1.6 3.8″ 98% 2.433

31 6h 50.3m +23° 38′ 26° Mo +1.6 3.9″ 98% 2.401

Jupiter 1 6h 04.1m +23° 13′ 8° Mo –1.9 32.2″ 100% 6.129

31 6h 33.0m +23° 03′ 30° Mo –1.9 32.9″ 100% 5.988

Saturn 1 14h 13.0m –10° 43′ 115° Ev +0.5 17.8″ 100% 9.357

31 14h 14.3m –10° 58′ 87° Ev +0.6 16.9″ 100% 9.841

Uranus 16 0h 46.5m +4° 13′ 101° Mo +5.8 3.6″ 100% 19.825

Neptune 16 22h 27.6m –10° 23′ 139° Mo +7.8 2.3″ 100% 29.214

Pluto 16 18h 41.4m –19° 53′ 166° Ev +14.0 0.1″ 100% 31.486

The Sun and planets are positioned for mid-July; the colored arrows show the motion of each during the month. The Moon is plotted for evening dates in the Americas when it’s waxing (right side illuminated) or full, and for morning dates when it’s waning (left side). “Local time of transit” tells when (in Local Mean Time) objects cross the meridian — that is, when they appear due south and at their highest — at mid-month. Transits occur an hour later on the 1st, and an hour earlier at month’s end.

Pollux

Arcturus

CORVUS

V I R G O

B O Ö T E S

L I B R A

L E O

H Y D R A

Regulus

P E G A S U S

CAPRICORNUS

AQUARIUS

Fomalhaut

Rigel

Betelgeuse

C A N I SM A J O R

P I S C E S

Sirius

O R I O N

Pleiades

TAURUS

Castor

Procyon

VegaGEMINI

H E R C U L E S

C Y G N U S

S C O R P I U S

O P H I U C H U S

Antares

SAGITTARIUS

AQUILA

C E T U SERIDANUS

A R I E S

Midnight2 am4 am6 am8 am10 am 8 pm 6 pm 4 pm 2 pm

+30°

+40°

–10°

–20°

–30°

–40°

+10°

+30°

0°

–10°

–20°

–30°

–40°

RIGHT ASCENSION4h6h 8h10h12h14h16h18h20h22h0h2h

DE

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+10°

LOCAL TIME OF TRANSIT10 pm

E C L I P T I C

Saturn

Uranus

Neptune

Pluto

Jupiter

Venus

Mars

Mercury

26

29July 3

12

1518

July22 – 23

Mercury

Venus

Mars

Jupiter

Saturn

Uranus

Neptune

Pluto 10"

July 1 11 21 31

16

16 311

16

16

311

July Right Ascension Declination Elongation Magnitude Diameter Illumination Distance


PA layout.indd 47 5/2/13 9:48 AM


OBSERVING Celestial Calendar

The Nearest Star for NorthernersBarnard’s Star is the closest known thing to the solar system after Alpha Centauri.

I have Alpha Centauri envy. The spec-tacular, zero-magnitude double star Alpha Cen AB, and its faint, red-dwarf tag-along Alpha Cen C (Proxima Centauri) 2°° to one side, are so far south at about declination –61° that they’re forever out of sight north of Miami or thereabouts.

So the next closest star ought to be on every northern observer’s life list. That’s Barnard’s Star, a red dwarf 5.98 light-years away in Ophiuchus, spectral type M3.5V. At visual magnitude 9.6 it’s a pretty easy pickup with a small scope, if you have good charts like the ones below.

Start from Beta (β) Ophiuchi, the east-ern shoulder of Ophiuchus. (Find his stick fi gure on our constellation map on pages 39 – 40, above the “Facing South” hori-zon.) From there jump 5° east to the dim, Hyades-like V known as Taurus Poniato-vii, “Poniatowski’s Bull,” marked in purple below. Its stars are 4th and 5th magnitude.

From the northwestern tip of the V, marked by the star 66 Ophiuchi, use your main scope to fi nd the 7th-magnitude triangle 1° to the northwest that’s marked on the maps and the photo at right. Nar-row in to Barnard’s Star from there.

Not only is Barnard’s Star the nearest nighttime star visible from north temper-ate latitudes, it’s also, by no coincidence, the star with the fastest proper motion in the sky. That’s how it caught the attention of Edward Emerson Barnard in 1916. It’s traveling north at 10.3 arcseconds per year, as shown by the yellow arrow on the close-up chart. Amateur imagers can measure its proper motion in a matter of weeks. Its visual position changes noticeably over several years. S&T senior editor Dennis di Cicco even made a project of measuring Barnard’s Star weaving through its 1.1″ of total annual parallax motion.

While you’re in the area, also take a

closer look at one of the stars of Taurus Poniatovii, 70 Ophiuchi. It’s a nearby double orange dwarf, magnitudes 4.2 and 6.2, spectral types K0V and K4V, current separation 6.1″. The pair makes a lovely sight in small scopes. The two stars, 16.6 light-years away, emit 50% and 9% as much visible light as the Sun, while Bar-nard’s Star glows with only 0.04% of the Sun’s visible luminosity.

No telescope? The closest star past Alpha Centauri that’s visible in binocularsis Lalande 21185, magnitude 7.5, located 8.3 light-years away in Ursa Major. Use the fi nder chart at skypub.com/lalande21185.

Use these charts to pinpoint Barnard’s Star, magnitude 9.6, off the eastern shoulder of Ophiuchus. On the wide chart at left, the small box shows the fi eld of the close-up below and the photo at right. The arrow shows more than 100 years of the star’s proper motion. The star is plotted at its 2013.5 position.

17h 58m 17h 56m18h 00m

+5°

+4.5°

Barnard's Star

66 Oph

1950

2000

2050

Star

mag

nitu

des

7

6

5

891011

+88

6

4

2

67

68

70

73

IC 4665

6535

O PH I U CHU S

T a u r u sP o n i a t o v i i

17h 50m 17h 40m18h 00m

+6°

+4°

+2°

0°

66Barnard's Star β

γ

Star

mag

nitu

des

4

3

5678

For a blink-comparison animation of the fi eld at right from about 1951 to 2013.3, see skypub.com/barnards. Many fainter stars show much smaller proper-motion hops of their own.

CC layout.indd 48 5/2/13 9:43 AM

Alan MacRobert


Asteroid OccultationOn the morning of July 29th, a 9.1-magnitude orange star in Aries will vanish for up to 3 seconds behind the invisibly faint asteroid 1074 Beljawskya, as seen along a narrow track running from west Texas through southern Missouri, Ohio, south-easternmost Ontario, and the Montreal area. The occultation happens within a few minutes of 8:56 UT. For a map, fi nder charts, more about asteroid occultations, and additional pre-dictions, see skypub.com/july2013asteroidoccultation.

The Barnard’s Star fi eld as imaged this spring. The frame is 1¼°° wide, matching the close-up chart at left.

Lunar OccultationOn the night of July 19–20, telescope users observing the waxing gibbous Moon from most of North America can watch the Moon’s invisible dark limb creep up to and occult the 4.4-magnitude star Xi Ophiuchi. Only Florida and the northern West miss out.

Some disappearance times: in western Massachusetts, 12:38 a.m. EDT; Atlanta, 12:32 a.m. EDT; Chicago, 11:10 p.m. CDT; Winnipeg, 10:50 p.m. CDT; Kansas City, 11:00 p.m. CDT; Austin, 11:07 p.m. CDT; Den-ver, 9:39 p.m. MDT; Los Angeles, 8:24 p.m. PDT. Start watching early.

S&T:

DEN

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Barnard’s Star

66 Oph

Need help matching star charts to what you see in your scope? Learn how: skypub.com/charts.



OBSERVING Celestial Calendar

JULY METEORSSeveral minor, long-lasting meteor showers with radiants in the southern sky are active during July, including the Alpha Capricornids, Piscis Austrinids, and Northern and Southern Delta Aquarids. All are weak, but together they increase the chance that a meteor you see late on a July night will be com-ing out of the south.

One of the things I like about amateur astronomy is that so much is going on over everyone’s heads that’s so easy to see — for the few who know how. The constel-lations (at least the brightest ones) are always old friends. And with binoculars you can spot things from your back porch that are known only to a very tiny elite of the world’s 7 billion people, most of whom never really look up.

Big Ophiuchus eternally holds his snake Serpens in the southern sky on June and July evenings (seen from north-ern latitudes). A diagonal row of four 2nd- and 3rd-magnitude stars marks his hands and the part of the snake between them (illustrated on pages 39 –40). The lower left of these stars is Eta (η) Ophiuchi, or

Sabik, magnitude 2.4. And did you know what lies just ¾°° southwest of it?

The deep-orange, Mira-type star R Ophiuchi won’t catch your eye in binoculars unless you’re looking for it. Often it won’t be there at all; it’s a long-period variable that spends some of its time as faint as 13th magnitude. But every 10 months, it rises into binocular visibility for several weeks. One of those times is now. R Ophiuchi should have a maximum centered around June 20th, predicts the American Associa-tion of Variable Star Observers (aavso.org).

How bright it will become is not very pre-dictable. In recent years R Oph has peaked as bright as magnitude 6.8 and as faint as 8.5, a factor-of-fi ve visual brightness diff er-ence, with no apparent rhyme or reason.

R Oph

Sabikη

60

67

7596

10194

85

60

77

83

24

1°

O PH I U CHU S

A Mira to AdmireUse the chart below to identify it and

estimate its magnitude when you take binocs out to have a look around. The chart gives nearby comparison stars’ magnitudes to the nearest tenth with the decimal points omitted.

Mira-type stars are pulsing red giants in a late stage of life. As they expand and contract they cool and heat, and this causes light-blocking molecules in their outer atmospheres to form and break.

And why do some stars pulse? The basic mechanism is simple. Deeper below the surface, a layer develops that becomes ionized as it heats, which turns the layer more opaque. This causes it to bottle in the heat coming from below, which drives the star to expand, which cools the critical layer, which loses its ionization and becomes transparent again, letting the heat out. Think of a fl apping lid on a pot of boiling water.

This process is simple in orderly, highly regular pulsating stars such as Cepheids and RR Lyraes. Matters are more complicated in the giant, cool Miras. They have those atmospheric molecules. Their surface gravity is weak, so they can become irregular blobs rather than clean spheres. They cool enough at minimum to shift almost all of their visible light into the infrared. And they may throw off smoky dust.

Take a look this evening and make a faithful, if odd and sometimes elusive, new friend that you can keep for life. ✦

So much for red dwarfs (previous page); here’s a noteworthy red giant. How accurately can you judge the brightness of R Ophiuchi as it swells and fades in June and July? This fi eld is 4° wide, a little smaller than the view in most binoculars and fi nderscopes. The numbers are comparison-star magni-tudes to the nearest tenth (decimal points omitted).



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OBSERVING Exploring the Solar System

Refl ecting on PanSTARRSRarely is such a bright comet so hard to see.

As Comet PanSTARRS (C/2011 L4) recedes from its brief pass through the inner solar system, we can now look back and sum up this bright but challenging visitor.

Discovered as part of the Panoramic Survey Telescope and Rapid Response System (Pan-STARRS) program, the 19th-magnitude comet was fi rst seen on June 5, 2011 in northern Scorpius. The comet was then about 8 astronomical units (a.u.) from the Sun and nearly two years from perihelion. What made the discovery particu-larly noteworthy was the initial orbit determination that

showed the comet would come as close to the Sun as the planet Mercury, implying an enormous rise in brightness by the time the comet rounded the Sun.

Word that a potentially brilliant comet is in the offi ng is always taken as exciting news, especially in the internet age. Bloggers, science news sites, and posts on count-less amateur forums heralded the comet’s approach with optimistic headlines such as “New comet may blaze with the brightness of Venus in the spring of 2013!”

Even though comets are known for being fi ckle when it comes to brightness predictions, in the months follow-ing PanSTARRS’s discovery it did appear to increase in brightness according to, or even exceeding, predictions. At the beginning of November 2012, as the comet headed into the evening twilight, it was roughly 10th magni-tude, and seemingly on its way to fulfi lling expectations. Together with the subsequent discovery of Comet ISON (C/2012 S1) in September 2012, some internet wags were dubbing 2013 to be the “Year of the Comet.”

Unfortunately, what had largely been ignored in the building excitement was that the orbit of C/2011 L4 was clearly hyperbolic, indicating that the comet was inbound from the distant Oort Cloud that surrounds our solar system. This would be Comet PanSTARRS’s fi rst visit to the inner solar system, and historically such comets tend to be poor performers that don’t live up to expectations. Recent history has presented us with several examples, including Comet Cunningham in 1942, and the infamous Comet Kohoutek in 1974 (April issue, page 32). Both were initially labeled as a “Comet of the Century,” and both ended up falling far short of the mark.

When Comet PanSTARRS emerged into the January 2013 morning sky, it was decidedly fainter than had been expected. During the ensuing weeks its rate of brighten-ing was also much slower than it had been in the preced-ing months. The comet was behaving in a manner typical of many “dynamically new” comets that are approaching the Sun for the fi rst time. Their initial outgassing when they are still far from the Sun is generated by volatile ices such as carbon monoxide and carbon dioxide, rather than

Despite achieving a respectable brightness, Comet PanSTARRS clung low near the western horizon for weeks following perihe-lion, dimming what otherwise might have been a brilliant display. The comet was also unusual in its general lack of an ion tail.S&

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N W

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ETSS layout.indd 52 5/2/13 9:44 AM


John E. BortleJohn E. Bortle is an internationally recognized comet observer and long-time contributor to Sky & Telescope.

water ice. But as these inbound comets cross a threshold heliocentric distance of around 2 to 1½ a.u., the outgassing due to water ice rapidly gains dominance and thereafter governs further brightness behavior. As a result, what ini-tially seems to be an intrinsically large, bright, and highly active comet far from the Sun, often turns out to be much less so as it enters the inner solar system.

This was indeed the case with Comet PanSTARRS, and predictions for the comet’s maximum brightness were scaled back. Nevertheless, by the end of February the comet was approaching 2nd magnitude as it swept through conjunction with the Sun and entered the eve-ning sky, hugging the western horizon as it moved north-ward. This orientation made PanSTARRS a diffi cult object to spot as it entered Northern Hemisphere skies.

Much like its brightness, early predictions for the comet’s tail development ended up being highly exagger-ated, especially when compared with computer simula-tions that peppered internet sites. During the early stages of the apparition, Comet PanSTARRS had an unusually high dust-to-gas ratio. With vaporizing water ices being the driving force for liberating dust particles from a comet’s nucleus, the scarcity of this icy volatile curtailed the unfurling of a spectacular tail as the comet drew

nearer the Sun. This also weighed heavily on the comet’s post-perihelion appearance.

During early March Comet PanSTARRS slipped ever deeper in evening twilight, making it increasingly diffi cult for observers to judge its brightness. This was compounded by a lack of suitable comparison stars nearby. The result was a dramatic spread in the comet’s reported brightness, which ranged as widely as magnitude –1 to +3 around the time of perihelion passage on March 10th. Values reported by experienced comet observers suggest that Comet PanSTARRS peaked close to magnitude +1.7, making it a fairly respectable comet, at least in terms of brightness.

At perihelion the comet passed just 15° from the Sun, rendering it very diffi cult for northern observers to spot in the strong evening twilight.

Viewing geometry kept PanSTARRS very low on the western skyline for many days following perihelion, forc-ing observers to search out locations with exceptionally low horizons. Those who succeeded were often struck by the comet’s small dimensions. Many reported that

S&T:

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Throughout the fi rst week of April, Comet PanSTARRS passed the large spiral galaxy M31 in Andromeda. Here it’s seen just after closest approach on the morning of April 4th at 9:00 UT.

ETSS layout.indd 53 5/2/13 9:44 AM

OBSERVING Exploring the Solar System


The Moon • July 2013

Librations

Schickard (crater) July 20

Kircher (crater) July 21

Malapert (crater) July 22

Boussingault (crater) July 23

DistancesApogee July 7, 1h UT

252,581 miles diam. 29′ 24″Perigee July 21, 20h UT

222,702 miles diam. 33′ 20″

NEW MOON July 8, 7:14 UT

FIRST QUARTER July 16, 3:18 UT

FULL MOON July 22, 18:16 UT

LAST QUARTER July 29, 17:43 UT

Phases

For key dates, yellow dots indicate which part of the Moon’s limb is tipped the most toward Earth by libration under favorable illumination.

S&T: DENNIS DI CICCO

July 20

21 2223

the intensely condensed coma spanned a mere 3′, and few could trace the relatively bright tail more than 1° or so from the comet’s head. Compared to bright comets in the past, PanSTARRS’s visual appearance proved largely disappointing. Several experienced observers said that it looked like a large, bright comet seen in miniature.

Those who were imaging the comet tended to fare better, and this advantage gained with time. The ability to digitally combine multiple short exposures revealed far more dramatic impressions of the comet than could be grasped through visual means. Noted Austrian astroimager Michael Jäger’s photograph on March 16th was among the earliest to illustrate the great breadth of PanSTARRS’s dust tail, along with a drastically weaker ion tail. His image made three days later proved even more striking, showing two narrow tails preceding the highly complex, broad, and strongly curving dust tail. Computer enhancement revealed roughly a dozen indi-vidual raylike striae, giving the comet’s tail an incredible appearance like a partially opened Japanese fan.

Fading to about 3rd magnitude by March 20th, PanSTARRS was still a naked-eye object very low in the western sky. As the close of March approached and the comet moved farther away from the Sun, an increasing number of impressive images began appearing online. A grand opportunity for photographers and visual observ-ers alike came during the fi rst week of April as C/2011 L4 swept past the Andromeda Galaxy. This was also the time that the comet was transitioning from being an evening object to one better seen before dawn. Although the comet’s brightness had fallen to about 4th or 5th magni-

tude, it’s extraordinarily broad dust tail spanned an arc of no less than 110°, even though its overall length didn’t exceed a stubby 3° to 4°. Shortly after that, PanSTARRS was lost to the unaided eye as it moved farther northward, becoming a circumpolar object visible to mid-northern observers using binoculars and telescopes.

As Comet PanSTARRS slips into history, eyes will soon turn toward another visitor whose story is yet untold. Comet ISON’s upcoming apparition at the end of this year remains a question mark. Will it be the object to fulfi ll the dreams of comet enthusiasts everywhere in the com-ing months? Only t ime will tell. ✦

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Imagers who planned ahead for the comet’s extremely low appa-rition were rewarded with photos that revealed roughly a dozen faint striae in its broad dust tail shortly after perihelion.

ETSS layout.indd 54 5/6/13 12:43 PM


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OBSERVING Deep-Sky Wonders

Many tales have been spun about the starry dragon winding through the northern sky, including the follow-ing myth of how he got there. In a great battle pitting the Titans and their allies against the gods of Olympus, a fear-some dragon set himself against Minerva, the goddess of wisdom and favorite child of Jupiter. Undaunted, Minerva seized the monster by its tail and whirled it up into the sky, where it became twisted around the axis of the heavens. Draco endlessly circles this axis as our world turns.

Let’s start our tour of the celestial dragon with the galaxy Messier 102, or should I say NGC 5866? Charles Messier’s collaborator Pierre Méchain reported M101 and M102 as separate galaxies but later stated that they’re one and the same. However, some researchers think that Méchain was right the fi rst time. The description of M102 is a fairly good match for NGC 5866 — and quite diff erent from the description of M101. It’s plausible that Méchain was in fact describing NGC 5866, and identifying M102 with this galaxy nicely fi lls out the Messier catalog. So I’ll enroll in that school of thought for the moment.

Draco, the DragonSome remarkable galaxies reside south of the Dragon’s body.

To track down M102, look for 3rd-magnitude Iota (ι) Draconis, also known as Edasich, which shines with the rich golden glow of evening sunshine. Through a fi nder-scope you’ll see two 7th-magnitude stars 1°° west-south-west of Edasich, and dropping about 2½° south from there will place a 16′-long curve of three 8th-magnitude stars to the west of center in your fi eld of view. Draw an imaginary line from the easternmost to the westernmost star in the curve, and then continue for three times that distance to reach M102.

M102 is a bright galaxy, easily seen in large binoculars and small telescopes. In my 130-mm (5.1-inch) refractor at 23×, it sits between the tines of a small but distinctive Y-shaped asterism. The ½°-tall Y opens southeast, and its brightest star is the 7th-magnitude topaz gem at its foot (northwest). M102 appears oval with a faint star hovering north of its northwestern tip. At 102× this pretty little gal-axy covers roughly 3′ × 1′ and grows progressively brighter toward the center. It’s now adorned with a second star, this one near the galaxy’s southwestern fl ank.

Through my 15-inch refl ector at 216×, M102 is quite

Tiny, faint NGC 5867 lurks south of Messier 102, also known as NGC 5866.

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Above: This very deep image of NGC 5907 shows what appears to be detritus from a galaxy collision long ago. Right: Here’s the author’s sketch of NGC 5907.

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DSW layout.indd 56 4/26/13 3:55 PM


Sue FrenchSue French welcomes your comments at [email protected].

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Angular sizes and separations are from recent catalogs. Visually, an object’s size is often smaller than the cataloged value and varies according to the aperture and magnifi cation of the viewing instrument. Right ascension and declination are for equinox 2000.0.

Galaxies in DracoObject Magnitude (v) Size RA Dec.

M102 9.9 6.4′ × 2.9′ 15h 06.5m 55° 46′

NGC 5867 16.2 0.3′ × 0.2′ 15h 06.4m 55° 44′

NGC 5907 10.3 12.6′ × 1.4′ 15h 15.9m 56° 20′

NGC 5963 12.5 3.3′ × 2.6′ 15h 33.5m 56° 34′

NGC 5965 11.7 5.2′ × 0.7′ 15h 34.0m 56° 41′

NGC 5971 13.8 1.6′ × 0.6′ 15h 35.6m 56° 28′

NGC 5969 14.4 0.4′ × 0.4′ 15h 34.9m 56° 27′

NGC 5777 13.3 3.1′ × 0.4′ 14h 51.3m 58° 59′

UGC 9570 15.2 0.9′ × 0.9′ 14h 51.6m 58° 57′

striking. Its profi le becomes a spindle that’s somewhat pointy at the tips and bulgy in the middle. The compara-tively large spindle is engulfed in a faint 3¼′ × 11/3′ halo, which is best seen when slowly sweeping the scope across it. The star off the southwestern fl ank seems to form a 1.4′isosceles triangle, pointing west-southwest, with two faint stars — except that the eastern one looks fuzzy. Boosting the magnifi cation to 247× confi rms this suspicion. Check-ing some references, I found that this nearly stellar spot is the galaxy NGC 5867.

At 345× a very faint star sits at the spindle’s northwest-ern point, and M102’s most enchanting feature makes an appearance — a dusky thread following the long axis of the spindle’s broad, central bulge. Amazingly, noted observer and author Stephen O’Meara has seen the slen-der dust lane girdling this galaxy as “a whisper of dark-ness” through his 4-inch refractor at 303×. O’Meara is in the camp of those who say that NGC 5866 is not M102.

The sky surrounding M102 is notable for hosting a few relatively bright fl at galaxies; that is, disk-shaped galax-ies that appear very thin because they’re seen edge-on. The nearest and brightest is NGC 5907, which dwells 1.4° east-northeast of M102. Returning to the arc of stars that helped us fi nd M102, you can sweep from the middle star through the easternmost star and continue for three times that distance to reach NGC 5907.

Through my 130-mm scope at 23×, NGC 5907 is a readily visible streak elongated north-northwest to south-southeast. At 117× the galaxy spans 9¾′ and is brighter on the eastern side of its long axis along the central 3¼′ of its length. This elongated core has a bright heart about 1′ long.

I’ve sketched each of the fl at galaxies with my 15-inch scope at 216× for easy comparison. The sketch of NGC 5907 (shown on the facing page) shows the central 15′ of my fi eld of view. Note the galaxy’s small, subtle nucleus and strange UFO-like profi le. NGC 5907 is one of the most alluring fl at galaxies I’ve seen, and our next two look much like smaller versions of it.

With such a long slim profi le, NGC 5907 has won the nicknames Splinter Galaxy and Knife-Edge Galaxy. Very deep images of NGC 5907 are quite stunning. Graceful loops of tidal debris enwrap the galaxy, like a snapshot of a pirouetting dancer swirling diaphanous scarves around her svelte form. A recent study (Jianling Wang et. al, February 13, 2012) published in Astronomy & Astrophys-ics indicates that these wispy streamers of stars may be lingering relics of the collision and merger of two similar-sized galaxies 8 to 9 billion years ago.

NGC 5907 and M102 are 50 million light-years distant, making them near neighbors of our Milky Way Galaxy and the brightest members of our sky tour.

Placing NGC 5907 in a low-power fi eld of view and pushing your telescope 2½° east will take you to the gal-

axy pair NGC 5963 and NGC 5965. NGC 5963 is usually eas-ier to spot, because most of its light is concentrated in its core. It shows up at 63× through my 130-mm refractor, with a faint star south-southeast of center near the galaxy’s edge. Just 9′ to the north-northeast, NGC 5965 is our second-brightest fl at gal-axy. It appears about 3¼′ long, tipped northeast, with an elongated core sprouting faint wings. At 102× NGC 5963 looks oval and wears a faint fringe. It’s about 1′ long and leans in the same direction as its neighbor.

The sketch of NGC 5963 and NGC 5965 also shows the central 15′ of the fi eld of view through my 15-inch refl ec-


OBSERVING Deep-Sky Wonders


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NGC 5965

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tor. Much more of NGC 5963’s ghostly halo is discernible through this scope. This visual halo consists of very loosely wound spiral arms.

My 130-mm scope at 102× holds two addi-tional galaxies in its fi eld of view, which rest 16′ southeast of their brighter neighbors. NGC 5971 is a very, very faint oval that’s roughly 1/3′ long, running southeast to northwest. NGC 5969 is an extremely faint, very small spot that I can only see with averted vision. The galaxies inhabit a busy star fi eld, and a chart showing very faint stars was necessary for pinpointing them.

Our fi nal fl at galaxy is NGC 5777, located 4.3°° west of Edasich and only 19′ south of a 5.5-magnitude yellow-orange star. My 130-mm refractor at 102× reveals a very faint, 2′-long streak that runs southeast to northwest and is best seen with averted vision. NGC 5777 is visible through my 10-inch refl ector at 43×, but 115× lengthens the galaxy to 2¼′ and discloses a brighter elongated core.

Through my 15-inch refl ector at 216×, NGC 5777 grows a starlike nucleus, and the galaxy’s core bulges out very slightly from the northeastern fl ank, as shown in the sketch above. A 14.5-magnitude star nudges the eastern

Above: Use this image to star-hop from the medium-bright galaxies NGC 5963 and 5965 to faint NGC 5971 and very faint NGC 5969. Right: The author’s sketch of NGC 5777 and UGC 9570 is at twice the scale of her sketch of NGC 5963 and 5965.

side of the galaxy’s northern tip. A second galaxy shares the fi eld of view, but I can only see the core — and even that requires averted vision. This little galaxy is the face-on, dwarf spiral UGC 9570. NGC 5777 and its companion are about 100 million light-years away from us.

Although the drawing of NGC 5777 and UGC 9570 was done at the same telescopic magnifi cation as the previous sketches, this one only shows the central 7½′ of my fi eld of view — half that of the other two sketches. I draw on unlined, 5 × 8-inch index cards. When I tried to cram 15′ of sky onto the card’s 4-inch circle, I found it diffi cult to pencil in details with the galaxy so small.

Draco keeps interesting company as he whirls around the axis of the sky, so be sure to visit his galaxy-spattered realm this summer. ✦

NGC 5965

NGC 5963

UGC 9570

NGC 5777



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Steve GottliebGoing Deep

NGC 6946 is the most pro-ductive supernova factory of the past century. Since the last Milky Way supernova explosion 140 years ago, NGC 6946 has churned out nine supernovae — in 1917, 1939, 1948, 1968, 1969, 1980, 2002, 2004, and 2008 — earning it the nickname “Firecracker Galaxy.” Hyperactive star formation runs rampant throughout the galaxy, from an inner nuclear starburst region to the outer disk, even producing an extraordinary super-star cluster (SSC) that’s visible in large amateur scopes.

The spiral galaxy

Unraveling NGC 6946This far-northern galaxy’s spiral arms are unusually easy to resolve.

1

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At declination +60°°, NGC 6946 lies far enough north to be circumpolar for most of the United States. It’s espe-cially well placed during the summer and autumn for northern observers to unravel its spiral arms.

NGC 6946 shines at magnitude 8.8 in a glittering star fi eld at the border of Cygnus and Cepheus, about 2° southwest of 3.4-magnitude Eta (η) Cephei. It shares a low-power fi eld with the 8th-magnitude open cluster NGC 6939. But at a distance of 15 to 20 million light years, the galaxy is roughly 4,000 times farther than its eyepiece neighbor. This odd couple is fairly easy to spot in my 15×50 binoculars. Both objects appear similar in size, though NGC 6939 displays a higher surface brightness.

Due to its location just 11° from the galactic plane, we view NGC 6946 through a veil of Milky Way dust. But because this late Hubble-type Scd spiral is relatively nearby and oriented nearly face-on to our line of sight, its spiral arms are unusually easy to resolve. In the fall of 1850, Irish astronomer William Parsons (Third Earl of Rosse) turned his 72-inch speculum-metal refl ector toward NGC 6946 and found a “new spiral, very fi ne but faint; 3 branches, of which two terminate in knots, a fourth branch north preceding very doubtful.” Later observations confi rmed the fourth arm, and a sketch by observing assistant Bindon Stoney (shown at left) captures the asymmetric arm structure as well as the two knots.

Under dark skies, an 8-inch telescope should reveal the brightest arm, and a 12- to 14-inch should show the overall spiral structure. In the early 1980s, I was mesmerized when my 13-inch displayed the two prominent arms curl-ing around the east side as well as a diff use western arm.

Through my 18-inch Dobsonian, the irregular halo of NGC 6946 spans 8′ and grows brighter to a 1.5′ central region. The nucleus, however, is just a very small, weak enhancement, pierced by a faint starlike point. The dominant arm is attached at the north side of the core and unfurls counterclockwise to the east, passing just south of a 13.5-magnitude star before terminating at a 10″ H II knot (labeled 1 on the photograph above).

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Lord Rosse’s assistant Bindon Stoney sketched NGC 6946 as seen in the 72-inch Leviathan of Parsonstown, Ireland. The knots at the ends of the spiral arms are labeled as in the photograph.

GD layout.indd 60 4/26/13 4:07 PM


The author resolved the knots labeled 1 and 2 in his 18-inch scope, knots 3–5 in his 24-inch, and the remaining three knots in Texan amateur Jimi Lowrey’s 48-inch.

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A side branch splits off on the northeast side and curls more tightly south, forming an inner arm halfway to the center.

A third, fainter arm emerges from the glow on the western side of the core and shoots sharply to the north. The fourth, southern arm never cleanly separates from the central glow, but a dip in brightness defi nes its outer edge as it sweeps west.

A number of fi eld stars are sprinkled across the face of the galaxy, including an 11.5-magnitude luminary at the southern edge of the halo. A 20″ pair of 13th-magnitude stars lies 2.4′ southwest of the nucleus. Just 1.5′ northwest of this pair I picked up a soft, 15″ knot (labeled 2) that could easily be missed. Studies reveal that this small-seeming patch is actually a huge stellar and gas complex spanning 2,000 light-years and containing more than a dozen tightly packed clusters, including a million-solar-mass SSC. At an age of only 10–15 million years, this supercluster is thought to be an early evolutionary stage in the formation of a classical globular star cluster.

The arms take on a clumpy texture in my 24-inch Dobsonian as more star- forming regions near the core

begin to resolve. These include two slightly brighter regions (labeled 3 and 4) along the main northern arm and an elongated enhancement at the southern tip of the inner eastern arm (5). Through Jimi Lowrey’s 48-inch in western Texas, the view approaches the photographic appearance, with additional isolated knots in the outer halo, including 6 on the west side, 7 on the northwest end, and 8 at the north edge.

Spiral arms are challenging, low-contrast features and require the darkest possible skies, patience, and careful study. For the best view of this galaxy’s overall structure, experiment with low to medium power (exit pupils from 2.5 to 4 mm). But to capture an H II region or the SSC, you’ll need to increase the magnifi cation and use the labeled image as a guide. ✦

Steve Gottlieb observes deep-sky objects from sites near his California home and around the world.

GD layout.indd 61 4/26/13 4:07 PM


in the world of amateur CCD imaging than SBIG, short for Santa Barbara Instrument Group. Founded by amateur astrono-mers in the late 1980s, the company built its reputa-tion on a succession of pioneering CCD autoguiders and astronomical cameras tailor-made for amateurs. A quarter century later SBIG’s core market still remains the amateur community, helping explain why there’s been lots of reader interest surrounding the launch of SBIG’s newest line of CCD cameras. Dubbed the STT Series, the completely redesigned cameras include a host of features

requested by astrophotographers. Among them are USB 2.0 and Ethernet computer connectivity, an internal image buff er, fast image downloads, advanced thermo-electric cooling, and modular integration with SBIG’s new fi lter wheels and autoguiding systems.

For this review I borrowed an early production model of the STT-8300 from the manufacturer. It features

No name is better known

New STT-8300 Camera

A redesign brings state-of-the-art features to SBIG’s new STT line of astronomical cameras.

S & T Test Report Dennis di Cicco

The STT-8300’s 5.4-micron pixels are well matched to short-focus instruments. This view of the Orion Nebula was shot with an 8-inch f/3 scope having a focal length of only 600 mm.

SBIG’sSBIG STT-8300 CCD CameraU.S. price: starting at $3,695.00

sbig.com

ALL PHOTOGRAPHS BY THE AUTHOR; IMAGE PROCESSING BY S&T: SEAN WALKER

STTR layout.indd 62 5/2/13 9:47 AM


WHAT WE LIKE:

Updated STT design, including mechanical, electronic, and software improvements

Modular integration with new fi lter wheels and autoguiding systems

WHAT WE DON’T LIKE:

Special care needed to ensure reliable connec-tion of the power supply to the camera (see text for details)

The STT-8300 and its self-guiding, eight-position fi lter wheel are operated by a single computer connection (either USB 2.0 or Eth-ernet). The “scope” port is for a conventional autoguiding cable.

With the 8-inch f/3 scope, the STT-8300 has an image scale of 1.85 arcseconds per pixel and a fi eld covering 1.7°° x 1.3°, ideal for imaging the galaxy pair M81 (bottom) and M82 in Ursa Major.

Kodak’s KAF-8300 CCD, which is one of most popular chips used by today’s amateurs. Much of the chip’s allure comes from its large array of 8.3 million 5.4-micron-square pixels. The relatively small pixels are well matched to short-focus telescopes, and they even work well with conventional camera lenses. SBIG off ers a variety of pack-age deals for the STT-8300. The one I tested includes the self-guiding FW8G-STT fi lter wheel, a set of eight 36-mm Baader fi lters (for LRGB and narrowband imaging), and a super-strong Pelican-Storm storage case. Priced at $5,985, this package costs about $1,000 less than if the pieces were purchase individually.

The camera and fi lter wheel weigh about 5¼ pounds (2.4 kg). Although this is a lot heavier than, say, a DSLR camera, it is well within the limits of most focusers sup-plied on modern telescopes made for imaging. I did most of my sky shooting with the STT-8300 attached to the Offi cina Stellare Veloce RH200 astrograph that I reviewed in last April’s issue, page 60 (you’ll fi nd additional images made with the STT-8300 there). I also tested the camera with several medium-format camera lenses fi tted to the STT-8300 with a lens adapter that I made myself. SBIG sells a lens adapter for Canon EOS lenses, but it only works with the STT-8300 camera body alone or with the standard FW8-STT fi lter wheel. The Canon lenses do not have suffi cient back focus to work with the added thick-ness of the self-guiding fi lter wheel I tested.

The self-guiding fi lter wheel is a new addition to SBIG’s line of products. Shown in the accompanying photos, it has a small CCD camera mounted on an adjust-able pick-off assembly placed ahead of the fi lters. As such, light from guide stars is not attenuated by the fi lters before reaching the guiding CCD. The pick-off mirror can be moved perpendicular to the telescope’s optical axis to avoid vignetting the STT-8300’s main imaging chip depending on the focal ratio of the telescope’s converg-ing light beam. I tested the system with camera lenses as fast as f/2, and it worked very nicely with the f/3 RH200 astrograph. Setting the pick-off mirror’s position and

focusing the guiding camera take a few minutes under a dark sky, and any extra time needed to get everything carefully adjusted is time well spent, since the only reason to change the guider’s position or focus is if you use dif-ferent telescopes or have fi lters of diff erent thicknesses.

Software and ConnectivitySBIG ships its cameras with printed manuals and the latest version of its venerable camera-control and image-processing program CCDOps. Versions of the software are available for Windows 2000 and above (including 32- and 64-bit systems) and Mac OS X 10.5 and above. There’s even a rudimentary version for LINUX, which the com-pany states is “for the adventurous.” SBIG also provides a nice program for installing and updating camera drivers on your computer. The documentation for these programs



S&T Test Report

is very clearly written, making it easy for those timid about computers to get everything working properly.

Although the user interface for CCDOps is starting to show its age, the program is full-featured and very robust. I’ve used various versions of it over the years with remarkable success, having never lost a single image to a software glitch. While I used the latest version for some of my STT-8300 tests, I did most of my image acquisition and processing with Diff raction Limited’s MaxIm DL, but only after I updated that software to the latest version (5.23) to make it compatible with the new SBIG camera. And for the record, I also had to update Software Bisque’s TheSkyX Profesional Edition to version 10.2.0 (build 6409) so its camera functions would work with the STT-8300.

I tested the STT-8300 with a variety of computer connections. At the telescope, I had a USB 2.0 cable run directly between the camera and my laptop computer. Most of my imaging, however, was done from a remote desktop computer in my house several hundred feet away from the telescope. I did this with a network USB hub — a now-discontinued Belkin product that plugs into any Ethernet port on my home network. Located next to the

The fi lter wheel attaches to the STT-8300 after removing the camera’s front cover. A new design ensures that fi lters precisely return to the same position each time they are moved, which is crit-ical for fl at-fi elding images when dust is on the fi lters. The self-guiding mecha-nism visible at lower right is described in the text.

Back-to-back 45-second expo-sures capture the record-breaking asteroid 2012 DA14 as it whizzed by Earth last Febru-ary 15th. The gaps between exposures are amplifi ed by the slow computer con-nection described in the text.

telescope, this hub provides USB ports without exceeding the distance limitations of standard USB cables. Except for being slower than a direct USB 2.0 connection, the Belkin hub worked fi ne with the STT-8300.

I also tried the camera’s Ethernet connection by plug-ging the camera directly into my home network with the same type of cable used to connect computers to the net-work. Initially I had some trouble with this arrangement, which I thought was due to my network fi rewalls. But it turned out that, unlike computers, the camera’s Ethernet connection has to be made before the camera is powered up in order for the system to be properly assigned a net-work IP address.

The Ethernet connection off ers some interesting pos-sibilities. First, any computer on the network can make a connection to the camera, regardless of distance between them, and you can operate the camera with appropriate software installed on the computer (CCDOps or MaxIm DL, for example), and this goes for computers using a wireless connection to the network. But the Ethernet con-nection also allows the camera to be controlled through its own built-in web server that you access by simply typing the camera’s IP address into the search fi eld of any web browser — even a browser on a smartphone! This eliminates the need for camera-control software on your computer or smartphone; you just need a web browser.

Although you can operate the STT-8300’s cooler, fi lter wheel, and exposure settings via the camera’s webpage, the setup is not optimized for advanced imaging. For example, you can’t run an automated sequence of fi ltered exposures. Nevertheless, the web access proved more use-ful than I initially anticipated. As mentioned earlier, I did most of my imaging with the camera run remotely from a computer in my house. But there were times I needed to shoot exposures at the telescope when focusing or trying to center a target on the CCD. It was super easy to do this using the web browser on my smartphone. As with any



new tool, once you have it you’ll likely think of interesting ways to use it.

Notes from the FieldI’ve only mentioned some of the STT-8300’s specifi ca-tions, since they are all available on SBIG’s website (www.sbig.com). You can also download all the user manuals for free from the website. After several months of test-ing the camera, I can comfortably say that it lived up to my expectations based on the company’s literature. One aspect of the camera, however, was diffi cult for me to test — the cooling. SBIG states that the STT-8300’s two-stage thermoelectric cooler can drop the CCD’s temperature as much as 55°°C below the ambient air temperature (and the camera is ready-made for water-assisted cooling if you need more). I chose to run the CCD at –25°C as a good balance between the KAF-8300’s imaging performance and a temperature I could reach even on warm nights. Nevertheless, there weren’t any warm nights during our recent New England winter. Indeed, on most nights the STT-8300 maintained its –25°C setting with the cooler running at less than 15% of its capacity.

As with other SBIG gear I’ve used in the past, the STT-8300 proved to be very robust and reliable. Occasionally I would get a “fi lter wheel error” when initially connecting to the camera using MaxIm DL on my remote computer.

I never isolated the problem, but it was likely due to the unusual way I set up my long-distance USB connection (described earlier). Regardless, simply making a second attempt to connect to the camera always worked.

In the grand scheme of things, the only quibble I have with the STT-8300 sounds rather minor, but it’s worth mentioning. SBIG uses a power connector with a locking collar that prevents the power cable from being accidently pulled out of the camera. That’s a very good thing. But if you don’t tighten the locking collar down snugly (some-thing that’s hard to do in the cold, especially if you have fat fi ngers like me), it’s possible to wiggle the power cable and break the connection, causing an electronic reset of the camera. That’s a bad thing. Once aware of this, I used needle-nose pliers to make sure the locking collar was tightened, and this eliminated the problem for good.

In many respects, the STT-8300 is the best SBIG cam-era I have ever used. Coupled with its self-guiding fi lter wheel, it’s a powerful platform ideally suited for imaging with typical setups used by today’s astrophotographers. The company is clearly continuing its well-deserved repu-tation of serving the amateur community. ✦

Senior editor Dennis di Cicco still covets his SBIG ST-4 autoguider/camera that he reviewed in the September 1990 issue, page 250.

The STT-8300 proved highly versatile for the author’s imaging projects, including a conventional color view (made with red, green, and blue fi lters) of the galaxy M101 (upper left), and a narrowband image (using H-alpha, O III, and S II fi lters) of the Crab Nebula (lower left). The narrowband image at right, totaling 25 hours of exposure with the 8-inch f/3 scope, captured the exceedingly faint fi lamentary structure of PKS 0646+06 in Monoceros. Listed as a supernova remnant, the virtually unknown object is 4½° east-northeast of the Rosette Nebula.



Gary SeronikTelescope Workshop

and I’ll say it again: view-ing the night sky in a telescope you’ve crafted with your own hands is the most rewarding experience in all ama-teur astronomy. Perhaps you’ve long suspected this but have held off taking the telescope-making plunge because it all seems so daunting. And you know what? It defi nitely can be. But with the right approach, making a telescope is as fun as it is rewarding. What follows is my simple advice for getting started as an amateur telescope maker (ATM).

Buy, don’t build. Okay, that sounds like ATM heresy, but one of the biggest mistakes fi rst-timers make is rush-ing a project just to have a telescope. Impatience encour-ages shortcuts and sloppiness — two qualities that rarely lead to satisfactory results. So it’s not a bad idea to buy your fi rst scope, and then make one. Not only will owning one give you have a better idea about how telescopes work, but you’ll be under less pressure to make one quickly.

Assemble fi rst. It’s much easier to get to know the ins and outs of telescope building if you don’t tackle every aspect of the project with your fi rst attempt. Buying a ready-made mirror and other components (focuser, mir-ror cells, tube, etc.) will smooth the bumps on the way up the learning curve. Of course, the more you build your-self, the greater the satisfaction. But even the assemble-only route is so rewarding that some telescope makers never wade deeper into the ATM’ing waters.

I’ve said it before

Getting Started Here’s some practical advice to ease your entry into the world of ATM’ing.

Get real. Be realistic about the project you tackle. Sure, a 16-inch Dobsonian is a “killer” deep-sky machine, but making and using one takes considerable eff ort. Is it really within a fi rst-timer’s capabilities? Perhaps. But don’t set the bar too high. An 8-inch is a great place to start since it represents an ideal balance between utility and ease of construction. After building a scope this size, you’ll be in a better position to take on a bigger project.

Avoid the internet. Don’t get me wrong, I love the abundant wealth of knowledge found online. But when it comes to making your fi rst telescope, the information not only has to be accurate, but it also has to arrive in the right order to be useful. For that reason, a good book that takes you through the whole process from start to fi nish is generally a much better guide than the random results that a Google search will turn up.

Buddy up! Books and online resources can off er plenty of great information, but there’s nothing like being at the elbow of someone engaged in making a telescope. Seeing how it’s done and knowing how it’s done are often two very diff erent things. Seek out your local astronomy club. Virtually every group has a few keen ATMs who will be more than happy to assist and off er pointers.

Grind your own mirror. This is the ultimate in tele-scope making. It off ers the most daunting challenges and the greatest rewards. Should you attempt it for your fi rst telescope project? Notwithstanding my preceding advice, I’d say go for it. Just be aware that it will take more time, patience, and skill, than the rest of the scope. Some people regard mirror making as merely a means to an end, and they question the wisdom of devoting the time and eff ort required to produce a fi ne optic. But this line of reasoning largely misses the point. You might as well ask why it’s worth the bother to go outside and look at the sky when you could stay indoors and view astrophotos on your computer. Making a telescope mirror is an enjoyable and deeply satisfying pursuit on its own. That the result is also the heart of a telescope that you can enjoy for your entire life, well, that’s just a very handsome bonus! ✦

Contributing editor Gary Seronik is an experienced telescope maker. Some of his creations (including his 6-inch f/9) are featured on his website, www.garyseronik.com.

The author’s 6-inch f/9 refl ector, which he built more than 20 years ago, is pictured waiting for dark-ness at the annual Mount Kobau Star Party. Although he had made several telescopes previously, this refl ector features the fi rst mirror he ground. It remains one of his most- cherished telescop es.

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Imaging Tips

Shootingwith

If you’ve been admiring the glori-ous images of galaxies, nebulae,

comets, and landscape-skyscape pairings produced in recent years, no doubt you’ve noticed that more and more of the photos have been captured with a modifi ed digital single-lens refl ex (DSLR) camera. Regular DSLRs have taken over the photography world, so what is “wrong” with the stock models that inspire some users to perform major surgery on a perfectly good camera?

To answer this question, let’s examine the main purpose of these cameras. DSLRs are designed to mimic the human

eye’s response to light, like their analog predecessor, color fi lm. Our eyes are sensitive to a narrow region of the elec-tromagnetic spectrum, from violet to deep red. DSLRs are designed to mimic this response to produce an image that closely reproduces what we see in everyday life.

But the CMOS detectors used in these cameras are sensi-tive to a much wider range of the electromagnetic spectrum than is visible to the human eye, from ultraviolet (UV) to infrared (IR) wavelengths. If this information were included in a typical snapshot, the image would look unnatural — foliage appears much brighter in infrared light than in visible wavelengths, and that would then distort the color balance of the resulting image. To compensate for this dif-ference, camera manufacturers use glass fi lters placed just over the detector that block this unwanted light, in order to better match the human eye’s color response.

The fi lters in DSLR cameras are excellent for produc-ing photographs of people, places, and other earthbound subjects, but one problem quickly arises when using these cameras for astrophotography. Many astronomical objects emit at wavelengths that are blocked by these stock

fi lters. In particular, vast clouds of ionized hydrogen gas fl uoresce in the deep red region of the spectrum at the hydrogen-alpha (Hα) wavelength of 656.3 nanometers. In all but one specialized DSLR model, the light at the wave-length of Hα light is cut to less than 20% by the internal fi lter, rendering invisible all but the brightest nebulae that permeate our galaxy in photographs.

To circumvent this issue, mechanically inclined ama-teurs often remove a camera’s internal fi lter or replace it with one better suited for astronomy. This greatly expands sensitivity to Hα and other wavelengths. Directions for

replacing your camera’s fi lters yourself can be found online, though this is not something you should attempt yourself if you’re inexperienced with microelectronics. It only takes one slip or static charge to completely destroy a DSLR camera! Also be aware that opening your camera body voids your factory warranty. For those who would rather not take a chance themselves, a few enterprising individuals (including myself) perform this service with a variety of options that can greatly increase the versatility of your DSLR camera. Let’s take a closer look at what each of these options can off er.

Choosing Your Modifi cationThere are three main options to consider when modifying your DSLR for astrophotography. The fi rst is to completely remove the internal blocking fi lter consisting of a thin pane of glass mounted in front of the imaging chip. But while this opens up the camera’s full range of spectral sensitivity, it also creates a few problems.

The fi lter’s glass increases the focal point of a con-verging light beam by 1/3 the thickness of the glass used.

Hap Griffin

DSLR Cameras

Expanding the spectral response of your camera opens up many new imaging opportunities.

Modi iedf

DSLRlayout.indd 68 5/2/13 9:43 AM


Removing the fi lter completely changes the eff ective optical distance between a lens and the sensor, which can prevent some camera lenses from focusing on distant subjects. Additionally, the camera’s autofocus mecha-nisms and its optical viewfi nder are no longer calibrated to the CMOS detector’s focal point.

For a camera dedicated solely to astronomical photog-raphy through a telescope, this isn’t a problem — tele-scopes focus well past the infi nity point, and critical focus on astronomical subjects is performed using live-focus mode, or with the aid of an external computer and spe-

As digital single-lens refl ex cameras (DSLRs) have overtaken the photo-graphic world, tinkering with their performance has also become increas-ingly popular. Author Hap Griffi n demonstrates how replacing the internal fi lter over your DSLR’s sensor can increase your camera’s sensitivity to wavelengths important in astronomy, particularly deep-red light where ionized hydrogen gas fl uoresces. A modifi ed DSLR is able to record much fainter reddish fi laments in nebulae such as Eta Carina (below) than are detectable using a stock camera (left).FE

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Imaging Tips

cialized software. But without any IR blocking, infrared light will throw out the color balance of your photos. Addi-tionally, refractive optics cause infrared wavelengths to focus at a slightly diff erent point than visible light, mak-ing star images appear bloated due to the out-of-focus IR view. Every telescope, whether it’s a Newtonian refl ector, Schmidt-Cassegrain, or Ritchey-Chrétien, requires addi-tional corrective optics to produce pinpoint star images across a large detector, so none is completely immune to this problem. An additional fi lter must then be used in the optical path to block this IR light but still allow the important Hα wavelength to pass.

A second solution is to replace the camera’s stock fi lter with one of clear glass of the same thickness, allowing all wavelengths to come to focus. This retains the camera’s autofocus capabilities and allows IR and UV light to be recorded along with visible light and Hα. There’s still the drawback of unnatural color response in daylight photog-raphy, as well as unfocused IR light bloating star images. These problems can be addressed using an additional fi lter in the optical path.

A third option is to replace the camera’s internal fi lter with one that still blocks UV and IR light, yet allows the light from Hα to be recorded virtually unimpeded. This allows you to still use all of your camera lenses and take daytime imagery. Although your color balance will be slightly off , you can easily fi x this by recording a cus-tom white balance setting in your camera. Instructions on how to accomplish this are included in every DSLR camera manual. To use a custom white balance, you must use the camera in one of its program or manual modes. Alternatively, an external color-correction lens fi lter such as the X-Nite CC1 available from MaxMax (www.maxmax.com), or the Astronomik OWB (Original White Balance) clip-in fi lter (www.astronomik.com), will allow the camera to be used in the fully automatic mode, just as it was before modifi cation.

Shooting with a Full-Spectrum CameraAs mentioned previously, a modifi ed camera can be more versatile than your stock camera. A full-spectrum modifi ed camera (when the internal fi lter is replaced with

The heart of every DSLR camera is its CMOS imag-ing sensor; shown here is the array from a Canon EOS T2i. All manufac-turers install a blocking fi lter directly in front of this chip to eliminate unwanted wavelengths that are mostly beyond the range of human vision.

Removing the blocking fi lter within your DSLR camera requires disas-sembling the entire body, which also voids any war-ranty. Imagers who desire greater sensitivity but are not mechanically inclined can send their cameras to a specialist such as the author, who can replace the internal fi lter with a selection of alternatives.

Below: Cameras with a full-spectrum modifi cation can image in a variety of diff erent wavelengths with the addition of vari-ous replaceable fi lters used in the optical path. This photo shows the distorted colors of a typical earthly scene when photographed with a modifi ed Canon EOS 40D and a Massa 720-nanometer IR-pass fi lter in front of the lens.

The author used the same modifi ed EOS

40D camera with the

addition of an Astronomik OWB clip-in fi lter to cap-

ture accurate colors of the

launch of the SpaceX

Dragon supply module on

its way to the International

Space Station last March.

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HAP GRIFFIN (2)



clear glass) is suitable for astronomical imaging, infrared photography, and regular daylight photography with the addition of various removable fi lters to attenuate the cam-era’s spectral response.

I often use a Canon EOS 40D DSLR with a fused-silica Astrodon full-spectrum modifi cation for all of my daylight photography, including rocket launches at Ken-nedy Space Center. To achieve a natural color balance in daylight with this modifi cation, I also use the Astronomik OWB clip-in fi lter. I can then use the same camera for astrophotography with the addition of a slightly diff erent Astronomik clip-in fi lter. It should be noted that this fi lter series is only available for Canon cameras, and Canon EF-S lenses will not work using the clip-in system.

Specialized ImagingSince the spectral response of a full-spectrum modifi ed DSLR is similar to that of a CCD camera, you can also use the camera for even more specialized photography, includ-ing narrowband imaging or IR photography. As opposed to full-color photography, narrowband, IR, and UV photog-raphy use special fi lters to isolate particular regions of the spectrum that are of interest. Infrared photography reveals the natural world around us in a wavelength range completely invisible to the human eye, which can be quite beautiful and artistic. UV photography also has special-ized uses, particularly for forensic investigators.

In astrophotography, the narrow spectral region where Hα predominates is also mostly free of light pollution from manmade sources and even moonlight, allowing you to shoot from urban locations and when a

bright Moon washes out most other deep-sky subjects. Astronomik also off ers a series of clip-in Canon fi lters that isolate many regions of the spectrum to take advan-tage of all these opportunities.

When imaging through these narrow specialized fi lters, be aware that your DSLR sensor uses an array of red, green, and blue fi lters (known as a Bayer matrix), with each pixel being sensitive to only one of these primary colors. This divides your detector into an array with 25% of the pixels having a red fi lter, 50% green, and 25% blue; the camera’s electronics interpolate this information to create your color image. Therefore, light through an Hα fi lter will only register on the red pixels. Similarly, UV-pass fi lters used with your modifi ed DSLR will record UV light on the blue pixels. Pixels of other colors will show only noise, so in processing you’ll need to use only the per-tinent color pixels for the narrowband fi lter in use. Most dedicated astronomical processing software for DSLR astrophotography, such as ImagesPlus (www.mlunsold.com) and MaxIm DL (www.cyanogen.com), has the ability to isolate these channels before color conversion.

Just as digital SLRs have revolutionized photography, modifying your camera greatly expands the possibilities of subject matter. And while there is some risk involved, more and more imagers are exploring the enhanced capa-bilities this change off ers. The usefulness and versatility of this high-quality tool to image the heavens and the world around us continues to grow. ✦

Visit Hap Griffi n’s website at www.imaginginfi nity.com for a complete list of DSLR modifi cation services.

The author captured sub-tle wisps of the Veil Nebula, NGC 6992, using a modi-fi ed Canon EOS 40D with a Baader UV/IR blocking fi lter installed directly in front of the CMOS detector.



Sean WalkerGallery

SHIMMER AND STREAKShannon BileskiA bright bolide lights up the southeastern sky over Lake Winnipeg during an auroral display.Details: Nikon D800 DSLR camera with 24-70mm lens at f/3.2. Single 8-second exposure recorded at ISO 800.

Gallery showcases the fi nest astronomical images submitted to us by our readers. Send your very best shots to [email protected]. We pay $50 for each published photo. See SkyandTelescope.com/aboutsky/guidelines.

GAL layout.indd 72 4/29/13 1:33 PM


◀ MEDUSA NEBULATerry Hancock & Fred HermannAbell 21 is an old planetary nebula roughly 1,500 light-years away in Gemini.Details: Astro-Tech AT12RC Ritchey-Chrétien telescope equipped with QSI 683 and QHY9M CCD cameras. Total exposure was 32 hours through color and narrowband fi lters.

◀▾ CLOUDS OF POLARISJohn DavisThis deep image reveals the extremely faint cirrus-like clouds of galactic nebulosity that permeate most supposedly “empty” regions of the Milky Way.Details: Takahashi FSQ-106EDX astrograph with SBIG STL-11000M CCD camera. Total exposure was 3¼ hours through color fi lters.

▾ THE SNOWMAN NEBULAMel MartinSharpless 2-302 in Puppis is a faint mix of reddish emission nebulosity with a small, bluish refl ection component along its northern edge.Details: Starizona Hyperion 12½ -inch astro-graph with SBIG STL-11000M CCD camera. Total exposure was 10 hours through Astrodon color fi lters.


CEPHEUS DUSTKerry-Ann Lecky Hepburn & Paul Mortfi eldAnother constellation saturated with faint dust is Cepheus. The orangish glow at center left is known as LBN 552. It consists of dust and gas illuminated from within by embryonic stars that have yet to burst forth from their dusty cocoon.Details: RCOS 16-inch Ritchey-Chrétien refl ector with an Apogee Alta U16M CCD camera. Total exposure was 24 hours through color fi lters. ✦

Gallery


Visit SkyandTelescope.com/gallery for more of our readers’ astrophotos.

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Woodland Hills (Page 9)Telescopes.net818-347-2270

TEXAS

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Tele Vue Optics, Inc. . . . . . . . . . . . . . . . . . . . .2

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Billions of PlanetsA leading researcher answers the most pressing questions about planets around other stars.

Social AstronomySocial media is quickly changing the way society interacts, a shift that is transforming the astronomical community.

Decoding the StarsThree women astronomers — Harvard “computers” paid as little as 25 cents an hour — laid the founda-tion for modern stellar astrophysics.

Amateur Imaging MilestoneAn Australian astrophotographer has imaged the disk that surrounds the star Beta Pictoris.

ITNI layout.indd 81 5/6/13 9:57 AM


Focal Point Howard J. Brewington

In 1961, at age 9, my parents gave me a 1.5-inch Sears refractor for Christmas. I didn’t realize that this gift made me an amateur astronomer; I just knew it was a great deal of fun pointing my little scope at the night sky. I recall gasping as the craters of the Moon came into focus and thought Galileo could not have been more surprised. Although I spent many hours observing, it was all done in fun and on a schedule dictated by my pleasure.

As an adult, in 1987, I became bored with general stargazing and decided to hunt comets. Looking for comets can be done at one’s leisure, but the most suc-cessful hunters go out as often as pos-sible. I spent as many as 8 hours per night at the eyepiece. Then, after a few hours of sleep, I would head to my full-time job.

The double-edged knife of success soon pulled me deeply into this dog-eat-dog world, as these fl eeting visitors found their way into my ever-vigilant eyepiece.

The comet bounty off ered by the IAU’s Edgar Wilson Award enticed me into dou-bling my eff orts, while I drifted farther and farther away from my childhood roots of doing astronomy just for fun. I hon-estly felt relieved when a turn of events caused me to retire my comet-hunting scope in 1999.

In 2002 I became an operator of the 2.5-meter telescope for the Sloan Digital Sky Survey at Apache Point Observatory in Sunspot, New Mexico. I had always believed the old proverb, “Choose a job you love, and you will never have to work a day in your life.” Although I love my

work, a job is still a job. Understand-ably, project management places great emphasis on effi cient data collection. So those carefree nights of standing in the backyard as a child with my little refractor seem more than a lifetime ago.

Yet I recently learned that one of my comets, 154P/Brewington, is returning and is predicted to reach 9th magnitude in late November 2013. I’m very excited! As I dust off the discovery instrument in preparation, I feel much like that 9-year-old boy waiting for the Moon to rise, so he could visit an old friend. And 50-plus years later, I realize with my returning comet that life has come full circle. I’ve now done astronomy for fun, for money, and lately for fun again. It feels great, and I’m glad to be back.

The action-reaction mechanism of ded-ication verses sacrifi ce plays a huge role in life’s accomplishments and failures. So to be successful, I invested a great deal of time in comet hunting and my astronomy career. But I somehow lost that love for the night sky that I enjoyed as a boy. Ironically, one of my comets is reigniting that old fl ame. Although I haven’t looked through my comet-hunting scope since 1999, and I have not truly done astronomy just for fun since 1961, I plan to take a nice, long, leisurely look at 154P. Like-wise, I anticipate my looming retirement years when I can once again stand in the backyard with my telescope and reconnect with my fi rst love, the night sky. ✦

To his knowledge, Howard J. Brewington is the fi rst and only person to discover a comet from South Carolina. F ive comets and one asteroid bear his name. He currently lives in southern New Mexico.

My Comet & Life Come Full CircleThe return of his comet rekindles the author’s passion for amateur astronomy.

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Sky & Telescope - July 2013