Astronomy 101The Solar System

Tuesday, Thursday2:30-3:45 pmHasbrouck 20

Tom Burbinetomburbine@astro.umass.edu

Course

• Course Website:– http://blogs.umass.edu/astron101-tburbine/

• Textbook:– Pathways to Astronomy (2nd Edition) by Stephen Schneider

and Thomas Arny.• You also will need a calculator.

Office Hours

• Mine• Tuesday, Thursday - 1:15-2:15pm• Lederle Graduate Research Tower C 632

• Neil• Tuesday, Thursday - 11 am-noon • Lederle Graduate Research Tower B 619-O

Homework

• We will use Spark• https://spark.oit.umass.edu/webct/logonDisplay.d

owebct• Homework will be due approximately twice a

week

Astronomy Information• Astronomy Help Desk• Mon-Thurs 7-9pm• Hasbrouck 205

•The Observatory should be open on clear Thursdays

• Students should check the observatory website at: http://www.astro.umass.edu/~orchardhill for updated information

• There's a map to the observatory on the website.

Final

• Monday - 12/14 • 4:00 pm• Hasbrouck 20

No class this Tuesday

• Space Station Bound: A Day in the Life of a Scientist Astronaut with Cady Coleman '91PhD

• Tuesday, October 13, 2009 • 4:00 pm • Engineering Lab II • Room 119 • Free Admission

HW #5 (replace)

• Due Today

HW #7

• Due next Thursday

HW #8

• Due next Thursday

October 9 (Tomorrow): 7:30 AM

• LCROSS (Lunar Crater Observation and Sensing Satellite)

• LCROSS’ spent Upper-Stage Centaur Rocket will crash into the Moon;s South Pole

• LCROSS will then follow into the Moon• Looking for water • http://www.youtube.com/watch?v=NQ8d2Oacv2M

New Rings around Saturn

• Seen in the infrared by the Spitzer Telescope• Made of dust and ice; Dust is 80 Kelvin• Lies some 13 million km from the planet• Tilted 27 degrees from main ring plane• 50 times more distant than the other rings and in a different plane. • Probably made up of debris kicked off Saturn's moon Phoebe by

small impacts.

Why infrared for dust?• Cold things give off more light in infrared than

visible

Blackbody• A black body is an object that absorbs all

electromagnetic radiation that falls onto it. • Perfect emitter of radiation• Radiates energy at every wavelength

http://www.daviddarling.info/images/blackbody.jpg

• Stefan-Boltzman Law - energy radiated per unit surface area of a black body in unit time is directly proportional to the fourth power of the black body’s temperature

• Wien’s Law - blackbody curve at any temperature has essentially the same shape as the curve at any other temperature, except that each wavelength is displaced, or moved over, on the graph

• Stars and planets act can be modeled as blackbodies

http://www.astro.ncu.edu.tw/contents/faculty/wp_chen/Ast101/blackbody_curves.jpg

Blackbody curves

• http://www.mhhe.com/physsci/astronomy/applets/Blackbody/frame.html

http://www.rap.ucar.edu/general/asap-2005/Thur-AM2/Williams_DoD_Satellites_files/slide0005_image020.gif

Power

• Power is in Joules/second = Watts

Stefan-Boltzman Law• Emitted power per square meter of surface = σT4

• Temperature in Kelvin• σ = 5.7 x 10-8 Watt/(m2*K4)

• For example, if the temperature of an object is 10,000 K• Emitted power per square meter = 5.7 x 10-8 x (10,000)4

• Emitted power per square meter = 5.7 x 10-8 x (1 x 1016)• Emitted power per square meter = 5.7 x 108 W/m2

Wien’s Law

• Wavelength of Maximum intensity of the blackbody curve peak = 2,900,000 nm

T (Kelvin)• λmax = 2,900,000/10,000 nm• λmax = 290 nm • 1 nanometer = 1 x 10-9 meters• λmax = 290 nm = 2.0 x 10-7 meters

When you observe an astronomical body

• You measure intensity• Intensity – amount of radiation

When you see an object in the sky

• You measure its brightness• Its brightness is a function of its

– Distance from Earth (can be calculated from orbit)If star:-Luminosity - is the amount of energy a body radiates

per unit timeIf planet– Albedo– Size

Inverse Square Law• The apparent brightness varies inversely by the

square of the distance (1/d2)• If the Earth was moved to 10 Astronomical Units

away, the Sun would be 1/100 times dimmer• If the Earth was moved to 100 Astronomical

Units away, the Sun would be 1/10000 times dimmer

If the Earth was moved to 1 x 108 Astronomical Units away, the Sun would be …

A) 1 x 10-12 times dimmerB) 1 x 10-14 times dimmerC) 1 x 10-16 times dimmerD) 1 x 10-18 times dimmerE) 1 x 10-20 times dimmer

If the Earth was moved to 1 x 108 Astronomical Units away, the Sun would be …

A) 1 x 10-12 times dimmerB) 1 x 10-14 times dimmerC) 1 x 10-16 times dimmerD) 1 x 10-18 times dimmerE) 1 x 10-20 times dimmer

Luminosity-Distance Formula

• Apparent brightness = Luminosity4π x (distance)2

Usually use units of Solar LuminosityLSun = 3.8 x 1026 Watts

Magnitude System

• Brighter –lower number

http://www.astronomynotes.com/starprop/appmag.gif

4 Vestabrightest asteroid

Magnitude difference Relative intensity0 11 2.512 6.313 15.84 39.85 10010 104

15 106

Initially

• Everybody observed with their eyes

Figure 7.1

Figure 7.2a

Parallel light Lens

Figure 7.2b

Why are Telescopes better than your eyes?

• They can observe light in different wavelength regions (eyes can only see visible light)

• They can collect more light than eyes• They can be built to compensate for the distorting

effects of the atmosphere

Figure 7.6

Refracting telescope

Reflecting Telescope

Reflecting Telescopes

Resulting image inverted

All large modern telescopes are reflectors

• Since light passes through the lens of a refracting telescope,

• You need to make the lens from clear, high-quality glass with precisely shaped surfaces

It is

• Its easier to make a high-quality mirror than a lens

Also,

• Large lenses are extremely heavy

Also

• Lens focuses red and blue light slightly differently• Called chromatic aberration

http://en.wikipedia.org/wiki/File:Lens6a.svg

Also

• Light can be absorbed by the glass as it passes through the glass

• Minor problem for visible, but severe for ultraviolet and infrared light

Size of a telescope

• Diameter of its primary mirror or lens• Light collecting area is proportional to the

diameter squared since• Collecting area = π r2

• E.g., 8-meter telescope

• Telescope that took image b is twice as big as telescope that took image a

• Larger the telescope, more detail can be seen

a b

• Telescope on Mauna Kea (14,000 feet high)• Telescope is Japanese Subaru 8-m telescope

Atmosphere

• Atmosphere can absorb light• Atmosphere can scatter light• Atmosphere can distort light (twinkling)

Twinkling

• Twinkling of stars is caused by moving air currents in the atmosphere.

• The beam of light from a star passes through many regions of moving air while on its way to an observer’s eye or telescope.

• Each atmospheric region distorts the light slightly for a fraction of a second.

Advantages of space-based telescopes

• It can be open 24 hours, 7 days of week• Do not have to worry about distorting effects of

atmosphere • There is no extra background of light due to

scattering of light in the Earth’s atmosphere• Observe in more wavelength regions

Figure 7.20

http://www.scienzagiovane.unibo.it/English/radio-window/images/radiazioni-em.jpg

• Infrared light absorbed by molecules

http://www.ucar.edu/learn/1_3_1.htm

Not all light from a star reaches Earth

Light in space can be affected by dust

http://www.ipac.caltech.edu/2mass/outreach/survey.html

http://en.wikipedia.org/wiki/File:Rayleigh_sunlight_scattering.png

It does not help

• That you are closer to the stars

To measure light

• In the past, they used photographic plates• Now they use CCDs (charge-coupled devices)• CCD are electronic detectors• CCDs are chips of silicons

Figure 7.5

CCDs• CCDs convert light into electrons

William Boyle George Smith

Shared the 2009Physics Nobel Prizefor their discovery

How do they work?• The CCD is made up of pixels.• As the light falls on each pixel, the photons become electrons

due to the photoelectric effect. The photoelectric effect happens when photons of light hit the silicon of the pixel and knock electrons out of place.

• These electrons are then stored.• Essentially, the charge in each row is moved from

one site to the next, a step at a time. This has been likened to a “bucket row” or human chain, passing buckets of water down a line.

• As these buckets of electrons reach the end of the line they are dumped out and measured, and this analog measurement is then turned into a digital value.

• Thus, a digital grid is made which describes the image.

Color separation for digital cameras• Colored filters

CCDs

• CCDs can collect 90% of photons that strike them• Photographic plates can only collect 10% of the

photons• CCDs are split into squares called pixels• Data is in electronic form

Hubble Telescope

• Can observe in visible, infrared, and ultraviolet wavelength regions

• Named after Edwin Hubble, the father of modern cosmology

Hubble (launched in 1990)

Telescope is the size of a school bus

2.4 m mirror

Initially• Hubble’s primary mirror was polished to the

wrong shape • Was too flat at the edges• Was barely 2.3 micrometers out from the required

shape (1/50 the width of a human hair)• Images were not focused as well as they could be• Later shuttle mission fixed this problem by

installing a number of small mirrors

http://dayton.hq.nasa.gov/IMAGES/SMALL/GPN-2002-000064.jpg

Jupiter

• http://video.nationalgeographic.com/video/player/science/space-sci/exploration/hubble-sci.html

Hubble replacement

• The first major components of the new James Webb Space Telescope are now being assembled.

• While Hubble is the size of a bus, the new James Webb will be the size of a jetliner.

• Will launch in 2014• James Webb is a former NASA administrator

during the Apollo program

• http://www.youtube.com/watch?v=SpkrVw_E6Nw

Any Questions?