Reading Clicker Q. Spectroscopy analyzing the light. What light gets through? Instruments in the Focal Plane. ASTR 1040 Accel Astro: Stars & Galaxies

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1 ASTR 1040 Accel Astro: Stars & Galaxies Prof. Juri Toomre TAs: Nicholas Nelson, Zeeshan Parkar Lecture 5 Tues 26 Jan 2010 zeus.colorado.edu/astr1040-toomre toomre Topics for Today What light does and does not get through atmosphere Telescopes in space -- and why Radio and x-ray x telescopes do it differently Overview of how Sun is put together Why is a star spherical,, and does not collapse? (Gravitational equilibration) Why does it shine? What is the energy source? (Fusion of H to He) New HW #3 Set out today,, HW #2 due Discussion question for Thur class: Pros and cons of a lunar observatory,, where to position it on the Moon (respond CULearn) Reading Clicker Q B. Which wavelength regions CAN be studied with ground-based telescopes? A. All light with wavelengths longer than ultraviolet B. Radio, visible, and very limited portions of infrared and ultraviolet C. All light with wavelengths shorter than infrared D. Infrared, visible, and ultraviolet What light gets through? B. Atmosphere protects us from most high energy photons But many very hot objects shine brightest in such UV, X-ray X and gamma-ray photons And cool star-forming regions are brightest in IR REMINDER Instruments in the Focal Plane How astronomers use light collected by a telescope: 1. Imaging use camera to take pictures (images) photometry measure amount and color (with filters) of light from object 2. Spectroscopy use spectrograph to separate light in detail into its different wavelengths (colors) 3. Timing measure how amount of light changes with time (sometimes in a fraction of a second) Spectroscopy analyzing the light Spectrograph reflects light off a grating: : finely ruled, smooth surface Light (by interference) disperses into colors This spectrum is recorded by digital CCD detector 1

2 Spectral resolution is vital but also costly in photons Light curves: : Studying changes with time Variable star MIRA: period ~331 days Which RADIATION gets through our ATMOSPHERE? GOOD LOUSY Atmospheric Absorption of Light 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! So what gets through our atmosphere? RADIO WAVES: mostly get through Thus radio telescopes are built on the ground Weather is not an issue - radio waves come right through the clouds Infrared Telescopes INFRARED can be absorbed by molecules like H 2 0, CO 2, CO, etc. Absorption is in specific wavebands, leaving windows where we can see through the atmosphere (best if high) Combination of ground- based, airplane, balloon, rockets, satellite 2

3 UV, X-rays X and Gamma-rays These all have enough energy to ionize electrons out of atoms or break apart molecules Heavily absorbed by the atmosphere Space or high altitude (balloon, rocket) observatories are necessary Clicker Q - galaxy B. REDSHIFTED In observing a distant galaxy, the H alpha spectral line of hydrogen (usually in the visible) is now in the IR portion of the spectrum.. What can you conclude? A. Galaxy is made purely of hydrogen B. Galaxy is moving away from us C. Galaxy is moving towards us D. Galaxy has very weak gravity Space Based Telescopes Hubble Space Telescope (HST) optical, UV Chandra X-ray Observatory REMINDER OF DEMO How do you point a space telescope in orbit? 1. Squirt from jets to change direction (hydrazine) 2. Torque by electric currents in big coils while flying through Earth s s magnetic field 3. Torque by electric motors spinning up or down reaction wheels SIRTF: Space Infrared Telescope Facility now SPITZER Launched August 03 Trails behind Earth to get away from Earth s s thermal spectrum 0.85m aperture, T ~ 5.5 K Cooled with liquid helium, had years worth, now used up (warmer phase) VISIBLE and UV visible: atmosphere is transparent but turbulent (seeing) HST: Small (2.5 meters), diffraction-limited Low orbit accessible by Shuttle, refurbishing means long lifetime ( ?) Costs: $5+ billion over 20 years, or times more than ground scopes Hubble Space Telescope (HST) 3

4 HUBBLE TROUBLE repaired by astronauts inserting corrective optics from Boulder HST Sharpness of Images HST Resolution: 0.05 arcseconds (D) Compare with best seeing ground-based observations at 0.5 arcseconds (B), and typical 2 arcsecond seeing (A). Pre-fix of HST image is (C). A B C D Nonvisible Light X-ray, UV, IR, Radio Most light is invisible to human eye Special detectors can record such light Digital images built using false-color coding X-Ray Telescopes 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 X-RayX Observatory Chandra X-ray X image of center of our Milky Way Galaxy Bigger view of Chandra s s X-ray X Imaging Chandra X-ray X Observatory (at L 2 Lagrangian) grazing reflections 4

5 Multi-energy x-ray x picture Radio Telescopes Biggest Single Dish Chandra: Supernova Remnant SNR: N132D 305 m Arecibo PR Green Bank Telescope (100+m) Radio Interferometry 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 Large Aperture Synthesis Very Large Array (VLA) NM 27 25m antennas 36 km baseline VLBA in Owens Valley CA continental baselines 10 25m dishes 5

6 One of 64 (80) 12m diam antennas 15km max separation (0.005 best resolution) ALMA: : Atacama Large mm-submm (M) Array ( mm) Very high desert Chile (altiplano 5000 m!) Reading Clicker Q What really is a light year? A. Year that has less calories B. Distance travelled by light in a year C. C. Time before some politicians tell the truth (as in It will be many light years before the truth is known.. ) D. Travel time for light to get to us from the Sun D. B Light year? B. DISTANCE travelled if moving at the speed of light (300,000 km/sec) Next to Our Nearest Star Chap 14 1 light-year = 9.46 trillion km = km 12 km Light travel time from surface of Sun to us is about 8 minutes Big Qs about the Sun (and any star) Why is a star ROUND? What keeps a star from collapsing inward? What keeps it shining? Why does it rotate and have varying magnetic fields? OVERVIEW of the Sun Round, rotates, burns H to He 6

7 EUV from SOHO Big System View of Sun core radiative zone convection zone photosphere chromosphere corona solar wind 7