Part II: Introduction to Observational Astronomy

July 23, 2004

July 23, 2004

What is Observational Astronomy?

July 23, 2004

How do astronomers know the things about the universe that

they claim that they know?

July 23, 2004

How do astronomers know the things about the universe that

they claim that they know?

• They observe the universe.• They do observational astronomy.• They use the scientific method to

develop theories that explain what is observed and seek out the laws under which the universe operates.

July 23, 2004

What is involved in doing observational astronomy?

July 23, 2004

What is involved in doing observational astronomy?

• Detecting and recording photons.• Characteristics of the detected photons are

used to infer physical properties of objects and nature of processes.

• Since humans are a visual life form, detected photons normally presented as an image.

• Collecting photons normally involves a telescope.

July 23, 2004

How is observational astronomy actually done?

There are three broad categories of activities…

• Astrometry

• Photometry (technically radiometry)

• Spectroscopy

July 23, 2004

How is observational astronomy actually done?

There are three broad categories of activities…

• Astrometry– positions, coordinates, motions

• Photometry (technically radiometry)

• Spectroscopy

July 23, 2004

How is observational astronomy actually done?

There are three broad categories of activities…

• Astrometry– positions, coordinates, motions

• Photometry (technically radiometry)– brightness, variability

• Spectroscopy

July 23, 2004

How is observational astronomy actually done?

There are three broad categories of activities…

• Astrometry– positions, coordinates, motions

• Photometry (technically radiometry)– brightness, variability

• Spectroscopy– Spectra, chemical composition, motion

July 23, 2004

Some ACTIVITIES illustrating observational astronomy…

as exemplified by the history of GRBs

July 23, 2004

The Vela Project

July 23, 2004

Vela Result Reported to the World

Current Date: 1973

Current Event: Organization of Petroleum Exporting Countries (OPEC) hikes oil prices tremendously in retaliation for Western countries' involvement in Yom Kippur War.

Klebesadel (LANL) publishes a paper in Nature and a presentation to the AAS reporting the discovery of 16 “cosmic” gamma-ray burst like events during the period of 1967-1972.

Klebesadel and Olsen

July 23, 2004

The First Questions• 16 recorded events have occurred.• These events appear to be coming from

random locations out in space.

What are some of the questions we scientists should be asking ourselves about these events?

Current Date: July 2 1967

Current Event: Racial violence in Detroit; 7,000 National Guardsmen aid police after night of rioting. Similar outbreaks in New York City's Spanish Harlem, Rochester, N.Y., Birmingham, Ala., and New Britain, Conn. (July 23).

July 23, 2004

The Possibilities

July 23, 2004

Early Balloon Missions

July 23, 2004

The CGRO MissionCurrent Date: April 5, 1991 Current Event: Europeans end sanctions on South Africa (April 15). South African Parliament repeals apartheid laws (June 5).

Compton Gamma -Ray Observatory is launched.

On board are 8 BATSE detectors designed to detect the position of GRB.

July 23, 2004

Alert! A BATSE burst just went off !

• A gamma-ray burst was just detected by BATSE. We have determined the object’s approximate location.

• We need some able bodied scientists to get the exact location of the burst.

Who is up for the challenge?

Current Date: January 20, 1992

Current Event: Yugoslav Federation broken up (Jan. 15). US recognizes three former Yugoslav republics (April 7). UN expels Serbian-dominated Yugoslavia (Sept. 22).

July 23, 2004

Astrometry

• Astrometry is the determination of the position of astronomical objects in the sky and how those positions change over time.

• Astrometry involves, in part, making maps of the sky Hyades from Hipparcos

satellite data

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Equatorial Coordinate System

• The equatorial coordinate system is the preferred coordinate system in observational astronomy.

• The equatorial coordinate system, like latitude and longitude, is also based on measures of angular separation from some arbitrary origin.

• The coordinate names are Right Ascension (RA) and Declination (Dec).

RA: 0 – 24 hours, Dec: -90o – +90o

Lon: 0o – 360o, Lat: -90o – 90o

July 23, 2004

Equatorial Coordinate System Units

• RA (0 to 24 hours) – 1 hour = 60 minutes– 1 minute = 60 seconds

• Dec (0 to +/- 90o)– 1o = 60’ (‘ = arcminutes)– 1’ = 60” (“ = arcseconds)

July 23, 2004

The Position ActivityAstrometry

• Using the RA and Dec plots given to your team determine the location of the gamma-ray burst to the nearest arcminute.

• The object labeled SAO 75945 has known coordinates.

• The object labeled GRB 910923 has an unknown position.

• See if you can determine the GRB’s absolute coordinates in the equatorial system.

July 23, 2004

Solution

RA = 03h 27.95m Dec = 22o 39.92’

July 23, 2004

Leap Forward 5 Years to 1996

By December 1996 ~1700 bursts had been detected by BATSE.

What conclusions can we draw based on this map?

July 23, 2004

Enter BeppoSAX• The question

arose, if GRBs are not concentrated evenly throughout our galaxy, then where are they?

• At the same time CGRO was in the peak of its life an Italian Dutch satellite named BeppoSAX was being launched.

We need to know another piece of information in order to determine where these GRBs are in the Universe and ultimately how much energy they expended during their short lived lives.

July 23, 2004

The Final Piece of the Puzzle

Distance!!!

MAP

DISTANCE

BRIGHTNESS

July 23, 2004

Alert: BeppoSAX has Just Detected a GRB!

• We have to move quickly - this GRB won’t be around for long.

• We need to confirm the GRB’s location and use a ground-based optical telescope with a CCD camera and spectrometer to determine how bright and how far away this GRB is.

July 23, 2004

BeppoSAX X-ray Image

Designation: GRB 970228Burst Time (UTC):05:00Burst Date (UTC): 28 February

1997Time Since Burst: 16 hoursCoordinates:

RA: 5h 01m 44s, Dec: +11o 46.7’Error Circle: 12’Equinox: J2000

Constellation: Orion

July 23, 2004

Step One: study the GRB at different wavelengths

• We are trying to identify the GRB by studying its emission at optical wavelengths. We hope to find another object at the same location that we can recognize (star, galaxy, etc.)

• We’ve been granted time on the 4.5m William Herschel Telescope the La Palma Observatory on the Canary Islands Spain.

• We need to analyze whatever data we get and determine the brightness as well as the spectral characteristics.

July 23, 2004

Photometry• Photometry is

the study of astronomical object’s brightness as a function of time

• One standard result of photometry is

the light curve

This is a lightcurve of GRB 910923.

July 23, 2004

Photometry - Lingo• Magnitude is a logarithmic

measure of the brightness of an object.

• Magnitude: The measured brightness of a celestial body.

– Dim objects have magnitudes of high numbers.

– Bright objects have magnitudes of low or even negative numbers.

– Applies to visible, IR and near UV light.

• If you don’t like the magnitude system send all hate mail to Ptolemy c/o some graveyard in Alexandria, Egypt.

• Difference in magnitude equation…

m1-m2 = -2.5 log (l1/l2)

Object Magnitude

Sun -26.8

Full Moon -12.6

Maximum brightness of Venus -4.4

Maximum brightness of Mars -2.8

Brightest star: Sirius -1.5

Second brightest star: Canopus -0.7

One of the brighter stars: Vega 0

Faintest stars visible in an urban neighborhood

+3.0

Faintest stars observable with naked eye

+6.0

Brightest quasar +12.6

Faintest objects observable with GORT

+20.0

Faintest objects observable

with HST

+30

July 23, 2004

Photometry - More Lingo• Luminosity: The

measured energy emitted each second by a celestial body.

– Applies to all wavelengths of light.

• Fluence: the integrated luminosity over some specified time duration.

• Photon Flux: the number of photons detected in a square meter-sized detector per second.

• Energy flux: the energy emitted per second (luminosity) that is deposited in a square-meter sized detector.

Object Luminosity

Sun 4 x 1026 W

Sirius 8 x 1027 W

Betelgeuse 2 x 1031 W

Accreting X-ray binary 1031 W

Supernova at peak 1037 W

Bright quasar 1038 W

Gamma-ray Burst peak

1045 W

Luminosity = Flux (4d2)

where d =distance to source

July 23, 2004

The Brightness ActivityPhotometry

In this activity you will determine the brightness of GRB 970402 using a clay star field, dissecting that star field, and quantifying the pieces.

A star field is a fancy name for an image, taken with a camera, on a telescope. It is a "field of stars".

July 23, 2004

Procedure• You now have a clay representation of a GRB

970402. The big clump of clay is the GRB and the clay sheet is background noise in the image.

• The other object is in the field has a known magnitude of 0. (Yes, zero, like the star Vega.)

• Can you figure out a way to subtract the background noise out to determine the brightness of the burst in relationship to the other object in the field?

• Remember… m1-m2 = -2.5 log (l1/l2)

July 23, 2004

Your Tools

• 1 triple beam balance• 1 sharp pencil• 1 12-inch ruler• 1 plastic knife (Safety first)

Determine the difference in magnitude between the two objects.

July 23, 2004

Rules

• You can not lift the red thing off of the black thing.

• This means you, Daryl!

July 23, 2004

Conclusion

What did you discover?

How bright is the object?

Great news, with the measurements you made our La Palma Technician says that the GRB is bright enough to take optical spectra.

Hopefully the optical spectra will be able to tell us more about these objects.

July 23, 2004

SpectroscopySpectroscopy is the study of how

bright things are over a range of wavelengths of light.

July 23, 2004

What can Spectroscopy tell us?

• Spectroscopy can tell us something about the temperature an astronomical object.

• Spectroscopy can tell us what elements are present in an object.

• Spectroscopy can tell us how far an object is away from us!!! (How???)

July 23, 2004

Red Shift

July 23, 2004

Spectroscopy of GRB 970228• On your desk is a jar of Jelly Belly® beans.• This candy represents the spectral energy

distribution of the GRB optical afterglow.• Separate the Jelly Belly® beans into their

corresponding wavelengths.• Then graph the results on the graph paper

provided.– Graph number vs. color with red on the left and

blue on the right.

July 23, 2004

What did you find out?

GRB 970228 Spectra

6

10

54

9

32

0

2

4

6

8

10

12

Red Orange Yellow Green Blue Indigo Violet

July 23, 2004

Now Compare Your Results to the Laboratory SpectraGRB 970228 and Laboratory Spectra

0

2

4

6

8

10

12

Red Orange Yellow Green Blue Indigo Violet

July 23, 2004

BREAK

• What differences do you see between your graph and the known source?

• What do you think is going on?

THINK GRB SPECTRUM

MYSTERY

July 23, 2004

Review: Astrometry

• Positions• Coordinates (right ascension and declination,

RA and DEC, galactic longitude and latitude)• Motion

• From where on the sky do the photons appear to originate?

July 23, 2004

Review: Photometry

• Brightness• Flux or magnitudes or number of photons• Colors• Variability• Lightcurves

• How many photons are actually detected from an object in a specified interval of time?

July 23, 2004

Review: Spectroscopy

• Spectrum• Spectral energy distribution (SED)• Emission lines, absorption lines• Chemical composition• Temperature• Radial velocity (red shifts, blue shifts)

• What is the relative distribution of detected photons of different wavelengths, frequencies, or energies?

July 23, 2004

Reflection and Debrief

July 23, 2004

Reflection and Debrief(Evaluate)

• Now what do we know?

• What are the big ideas here?

• What do our students need to know?

• Is there anything else we need to know?

• Misconceptions

(take notes)

July 23, 2004

Reflection and Debrief (Evaluate)

• What are some of the effective ways to teach these topics?

• Standards???

(take notes)

July 23, 2004

The Global Telescope Network

http://gtn.sonoma.edu

July 23, 2004

What is the GTN?• The GTN is a network of individuals and

organizations interested in supporting several NASA space observatories by obtaining ground-based observations.

• The GTN has been designed to allow students, educators, and others to become involved in doing real science and to contribute to the science goals of several NASA missions.

• Here is the GTN paradigm…

Elk Creek Observatory

The Global Telescope NetworkThe Global Telescope Network

July 23, 2004

The Science of the GTN

• Observational astronomy with small telescopes.• Science objectives focused on obtaining synoptic surveillance of

objects which will be observed by the NASA missions we support.

• Program objects are variable and can change in brightness unexpectedly.

• Program objects are the blazars and the polars.• Obtain CCD images of these objects and analyze the images.

– Determine magnitudes– Do photometry– Obtain light curves

Telescope Observing Activity…

July 23, 2004

So you want to do some observing?

We are interested in digital images obtained using CCDs with small to moderate size telescopes.– The costs are not… impossible.– It can be fun.– It can be exciting.– The images can readily be used to produce

significant scientific results.

July 23, 2004

What can you do relatively easily with CCD images

obtained with a telescope?

July 23, 2004

What can you do relatively easily with CCD images

obtained with a telescope?• You can enjoy obtaining detailed images of those

exotic deep sky objects you have heard about.• You can do photometry.

– Variability– Lightcurves– Discovery

• You can also do astrometry (easy!) and even spectroscopy (more challenging).

July 23, 2004

Some Deep Sky Images

July 23, 2004

Examples of Blazar Lightcurves

B2 1215+303

July 23, 2004

Your Mission… should you choose to accept it

July 23, 2004

Your Mission… should you choose to accept it

You have been invited to submit an observing proposal for the robotic telescope system GORT (GLAST Optical Robotic Telescope)

If your proposal is accepted, you will enter the specifications for the objects you wish to observe into the telescope control system.

The system will acquire the images you specify.

You get to see (and keep) the images!

July 23, 2004

What is GORT?

July 23, 2004

Here is GORT

GLAST Optical Robotic Telescope

July 23, 2004

Here is the business end of GORT

July 23, 2004

The image fields you will specify for the activity…

1. An image of some field or object in the sky that is of interest to you (fun).

– Messier object, for example– Other resources are available– Use your imagination

2. An image of a GTN program object (science)

– A GTN blazar– A GTN polar

July 23, 2004

What will you need to specify in your observing proposal?

• Object name or designation• Object coordinates (RA and DEC)

– Nearest second of time for RA, neatest second of arc for DEC, equator and equinox for 2000.0

– Need to be accurate!

• Exposure times– Seconds or minutes– Not too long (saturated) or too short (not there)

• Filters (clear, V, R, I)• Justification for selecting this object

– What do you think you will see?

July 23, 2004

The tools you will have available for the activity…

1. Lists of sky objects– Catalogs– Web links

2. Sky simulation software3. List of instrumental limitations and

recommendations4. Tutorials and resource materials

– What do you need to know?– What would you like to know?

July 23, 2004

Instrumental LimitationsGuidelines for Using GORT

1. Angular field of view of an image is 10 arcminutes2. Maximum exposure time for an untrailed image is

90 seconds3. A 1 minute exposure can probably record objects

as faint as 18th magnitude4. Objects brighter than 8th magnitude are likely to be

saturated for exposure times longer than 1 second5. Exposure times as short as 0.001 second may be

specified.

July 23, 2004

An expanded description and an online version of this activity is available for classroom use.

• Expanded description– The expanded description includes questions to engage the

audience and some background material.– Expanded Activity Description

• Online version– The online version contains extensive links to resource

materials.– http://gtn.sonoma.edu/public/resources

July 23, 2004

Presentation of Results

• Groups will have an opportunity to present results. (Monday Night)– You should be able to tell us about

the objects in your images.– You should be prepared to answer

questions about what you have done.

• Prizes for the best science and for the most interesting images

July 23, 2004

CHIPS Education Brief

• Exploring the Interstellar Medium • Experiment “What is the difference between Heat and

Temperature?” Weekend Homework• Make sure to get your Dihydromonoxide cooling and

containment devices, average particle energy data displays, and temporal distance measuring devices for your apartment.

• Suggestion for Homework optimization: Perform all 5 room temperature/open air tests first and at the same time. It can take over an hour for phase changes to occur at room temperature.

July 23, 2004

Backup follows

July 23, 2004

What things do you need to know or worry about for a

successful proposal?

July 23, 2004

What things do you need to know or worry about for a

successful proposal?

• It must be dark– After twilight (sunset), before dawn (sunrise)

• Object must be above your telescope horizon at the time you are able to observe

• Object must not be too large or too small for the field of view of your images

• Object must not be too faint or too bright• Exposure times must not be too long or too short

July 23, 2004

How can you determine when an object is up at night?

July 23, 2004

How can you determine when an object is up at night?

• Ask an amateur astronomer.• Professional astronomers tend not to know these

things… unless…• Ask someone who operates a telescope on a regular

basis.• Use sky simulation software.

– TheSky– Voyager– Starry Night– YourSky on the web

July 23, 2004

How do you determine a magnitude??

July 23, 2004

How do you determine a magnitude??

• Aperture photometry

• All magnitudes are really relative– With some agreed zero point– Comparison stars or sequence stars

• Magnitude equationm1-m2 = -2.5 log (l1/l2)

• Image analysis software systems

July 23, 2004

Image Analysis Software

• Maxim

• CCDSoft

• AIP (Astronomical Image Processor)

• HOU (Hands On Universe)

• Mira

• IRAF

• SIP (Sky Image Processor, on the web)

July 23, 2004

How do you determine what the magnitude should be?

July 23, 2004

How do you determine what the magnitude should be?

• You do not know… – variable objects– but you should determine your measurement errors

• The GTN will maintain statistical summaries.• The AAVSO maintains database of current

magnitude estimates and measurements (also lightcurves)

• Outbursts, flares, declines, flickering