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ASTR 1040 ASTR 1040 AccelAccel AstroAstro: : Stars & GalaxiesStars & Galaxies

Prof. Prof. JuriJuri ToomreToomre TA: Nick FeatherstoneTA: Nick FeatherstoneLecture 5 Tues 30 Jan 07Lecture 5 Tues 30 Jan 07

zeus.colorado.edu/astr1040zeus.colorado.edu/astr1040--toomretoomre

Topics for Today Topics for Today

•• Twinkle and absorption Twinkle and absorption by our atmosphereby our atmosphere•• What light gets through, what does notWhat light gets through, what does not•• Telescopes in spaceTelescopes in space ---- and whyand why•• Radio and xRadio and x--ray telescopes do it differentlyray telescopes do it differently•• Finish readingFinish reading Chap 14Chap 14 (Our Star .. the Sun)(Our Star .. the Sun)•• Discuss next class:Discuss next class: What are pros and cons What are pros and cons

of a of a Lunar Astronomical ObservatoryLunar Astronomical Observatory

Clicker Q: Radio WavesClicker Q: Radio Waves•• You are listening to a radio station You are listening to a radio station

broadcasting at a FM frequency of 97 broadcasting at a FM frequency of 97 MhzMhz. . Which is true?Which is true?

•• A.A. The radio waves from the station have a wavelength of 97 million meters.

•• B.B. The “radio waves” received by your radio are not light waves, but rather a special kind of sound wave.

•• C.C. The radio station broadcasts it signal with a power of 97 million watts.

•• D.D. The radio waves are causing electrons in your radio’s antenna to move up and down 97 million times per second.

D.D. RadiosRadios

•• You are listening to a radio station You are listening to a radio station broadcasting at a frequency of 97 broadcasting at a frequency of 97 MhzMhz. . Which is true?Which is true?

• D. The radio waves are causing electrons in your radio’s antenna to move up and down 97 million times per second.

fc ⋅= λD.D.

Wavelength = Speed of light / frequencyWavelength = Speed of light / frequency= 3.0 x 10= 3.0 x 1010 10 cm seccm sec--11 / 9.6 10/ 9.6 1077 secsec--11

= 312 cm= 312 cm

Problems in Looking Through Our Problems in Looking Through Our AtmosphereAtmosphere

•• Many wavelengths are Many wavelengths are absorbedabsorbed (just don(just don’’t make t make it through to surface)it through to surface)

•• Turbulence in atmosphere distorts lightTurbulence in atmosphere distorts light::–– stars appear to stars appear to ““twinkletwinkle””–– angular resolution is degradedangular resolution is degraded

•• ManMan--made light is reflected by air particlesmade light is reflected by air particles, , yielding bright night skyyielding bright night sky–– this is this is light pollutionlight pollution

Light PollutionLight Pollution

90% of Earth90% of Earth’’s population cannot see the Milky Ways population cannot see the Milky Way

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How many light bulbs does it take to How many light bulbs does it take to screw up an astronomer?screw up an astronomer?

An immediately curable pollution: simply turn the lights off!

Stop “uplight”, glare: wastes billions of $$ in energy, use “low pressure sodium”

Several famous observatories are now useless…

LA Basin View from Mt. Wilson LA Basin View from Mt. Wilson Observatory, 1908 and 1998Observatory, 1908 and 1998

Quest for Good Weather and SeeingQuest for Good Weather and Seeing

•• Mauna Kea, Big Mauna Kea, Big Island of HawaiiIsland of Hawaii, , 14,00014,000’’ elevation, elevation, middle of the middle of the PacificPacific

•• Dry, high, dark and Dry, high, dark and isolatedisolated. Best on . Best on the planet?the planet?

.

Sites in Arizona, Chile,Sites in Arizona, Chile,Canary Islands, EuropeCanary Islands, Europe….

Adaptive Optics (AO) Adaptive Optics (AO) –– ““dede--twinkletwinkle”” starsstars• Wavefronts of star light are deformed by atmosphere• Can distort shape of mirror (very fast) to correct for

distortions by atmosphere – hot new technology

AO mirror OFFAO mirror OFF AO mirror ONAO mirror ON

Two stars!Two stars!

Which RADIATIONWhich RADIATIONgets through ourgets through ourATMOSPHERE ?ATMOSPHERE ?

GOODGOOD

LOUSYLOUSY

Atmospheric Absorption of Atmospheric Absorption of ““LightLight””• Earth’s atmosphere absorbs most types of light

(not entirely bad, or we would be dead!)• Only visible, radio, and some IR and UV light get

through to the ground

To observe other wavelengths, must put telescopes in space!To observe other wavelengths, must put telescopes in space!

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So what gets through our atmosphere?So what gets through our atmosphere?

•• RADIO WAVESRADIO WAVES:mostly get throughmostly get through

•• Thus radio telescopes are Thus radio telescopes are built on the groundbuilt on the ground

•• Weather is not an issue Weather is not an issue --radio waves come right radio waves come right through the cloudsthrough the clouds

Infrared TelescopesInfrared Telescopes•• INFRAREDINFRARED can be can be

absorbed by molecules absorbed by molecules like Hlike H220, CO0, CO22, CO, etc. , CO, etc.

•• Absorption is in specific Absorption is in specific wavebands, leaving wavebands, leaving ““windowswindows”” where we can where we can see above the see above the atmosphereatmosphere

•• Combination of groundCombination of ground--based, airplane, balloon, based, airplane, balloon, rockets, satelliterockets, satellite……

UV, XUV, X--rays and Gammarays and Gamma--raysrays•• These all have These all have enough energy to ionize electronsenough energy to ionize electrons out of out of

atoms or atoms or break apartbreak apart moleculesmolecules

Heavily absorbed by the atmosphere Heavily absorbed by the atmosphere

•• Space or high altitude (balloon, rocket) observatories are Space or high altitude (balloon, rocket) observatories are necessarynecessary

Clicker Q Clicker Q -- galaxygalaxy•• In observing a distant galaxy, the In observing a distant galaxy, the H alpha H alpha

spectral line of hydrogenspectral line of hydrogen (usually in the (usually in the visible) is now in the visible) is now in the IR portion of the IR portion of the spectrumspectrum. What can you conclude?. What can you conclude?

•• A. Galaxy is made purely of hydrogenA. Galaxy is made purely of hydrogen•• B. Galaxy is moving away from usB. Galaxy is moving away from us•• C. Galaxy is moving towards usC. Galaxy is moving towards us•• D. Galaxy has very weak gravityD. Galaxy has very weak gravity

B.B.REDSHIFTEDREDSHIFTED

Space Based TelescopesSpace Based Telescopes

Chandra XChandra X--ray Observatoryray ObservatoryHubble Space Telescope (HST)Hubble Space Telescope (HST)

optical, UVoptical, UV

SIRTF: Space SIRTF: Space InfraredInfraredTelescope FacilityTelescope Facility

now now SPITZERSPITZER

•• Launched August 03Launched August 03•• Trails behind Earth to get Trails behind Earth to get

away from Earthaway from Earth’’s thermal s thermal spectrumspectrum

•• 0.85m aperture , T ~ 5.5 K0.85m aperture , T ~ 5.5 K•• Cooled with liquid heliumCooled with liquid helium, ,

22--5 years worth5 years worth

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Hubble Space Hubble Space Telescope (HST)Telescope (HST)

•• VISIBLE and UVVISIBLE and UVvisible: atmosphere is atmosphere is transparent but turbulent transparent but turbulent (seeing)(seeing)

•• HST: Small (2.5 meters), HST: Small (2.5 meters), diffractiondiffraction--limitedlimited

•• Low orbit accessible by Low orbit accessible by Shuttle, refurbishing means Shuttle, refurbishing means long lifetime (1990long lifetime (1990--2010+?) 2010+?)

•• Costs: $5 billion over 20 Costs: $5 billion over 20 years, or 10 years, or 10 -- 100 times 100 times more than ground scopesmore than ground scopes

How do you point a space How do you point a space telescope in orbit ?telescope in orbit ?

ANGULAR MOMENTUM ANGULAR MOMENTUM DEMONSTRATIONDEMONSTRATION

1.1. Squirt from jetsSquirt from jets to change direction to change direction (hydrazine)(hydrazine)

2.2. TorqueTorque by electric currents in big coilsby electric currents in big coilswhile flying through Earthwhile flying through Earth’’s magnetic fields magnetic field

3.3. TorqueTorque by electric motors spinning up by electric motors spinning up or down or down ““reaction wheelsreaction wheels””

HST Sharpness of ImagesHST Sharpness of Images

•• HST Resolution:HST Resolution: 0.05 0.05 arcsecondsarcseconds (D)(D)

•• Compare with Compare with ““best seeingbest seeing”” groundground--based observations based observations at 0.5 at 0.5 arcsecondsarcseconds (B), and (B), and ““typicaltypical”” 2 2 arcsecondarcsecond seeing seeing (A). Pre(A). Pre--fix of HST image is (C).fix of HST image is (C).

A B C A B C DD

HUBBLE TROUBLEHUBBLE TROUBLE

repaired by astronautsrepaired by astronautsinserting correctiveinserting correctiveoptics from Boulderoptics from Boulder

XX--Ray TelescopesRay Telescopes –– do it their own way!do it their own way!• X-ray photons can pass right through a mirror• Such photons can only be reflected at shallow

angles, like “skimming stones” off water surface

Chandra XChandra X--RayRayObservatoryObservatory

Bigger view of ChandraBigger view of Chandra’’s Xs X--ray Imagingray Imaging

““grazing reflectionsgrazing reflections””

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Chandra XChandra X--ray Observatoryray Observatory (at L(at L22 LagrangianLagrangian)) ““NonvisibleNonvisible”” Light Light –– XX--ray, UV, IR, Radioray, UV, IR, Radio•• Most light is invisible to human eyeMost light is invisible to human eye•• Special detectors can record such lightSpecial detectors can record such light•• Digital images built using falseDigital images built using false--color codingcolor coding

Chandra XChandra X--ray image of center of our Milky Way Galaxyray image of center of our Milky Way Galaxy

Radio Telescopes Radio Telescopes –– Biggest Single DishBiggest Single Dish

305 m305 m Arecibo PRArecibo PR

Radio Radio InterferometryInterferometry –– many small look big!many small look big!• Two (or more) radio dishes observe the same object• Signals from each “interfere” with each other• Can construct image whose angular resolution is like

that from a huge dish!

VLA VLA –– Large Aperture SynthesisLarge Aperture Synthesis

Next to Our Nearest Star Next to Our Nearest Star Chap 14Chap 14