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Transcript
INTRO In astronomy, observation usually precedes theory. Ex/ New solar syst.; acc. univ. Telescopes have grown in size and complexity and now cover the entire EM spectrum I. Optical Telescopes A. Telescope: A “light bucket” used to capture incoming photons & concentrate them into a focused beam for analysis. B. Types of Telescopes 1. Refractors: A glass lens bends (refracts) incoming light rays to a focus. Eyepiece magnifies. Yerkes Observatory 2. Reflectors: A curved mirror (the primary mirror) reflects incoming rays to a focus. Eyepiece magnifies. D. Reflector Design 1.Newtonian: Secondary mirror reflects light to side eyepiece. Subcategory: Dobsonian 2. Cassegrain: Secondary mirror reflects light back thru a hole in the primary mirror. II. Telescope Size & Resolution A. Light-gathering power: Larger collecting area - brighter image. 2 1. Brightness ~ Diameter Ex/ 10” aperture is 25 x brighter than 2” aperture (or 25 x faster exposure) 2. Largest: VLT in Chile (16 m) Keck I & II in Hawaii (14 m) TMT (2018); Giant Magellan Telescope (2016) Ch. 5 Example Problem How long would it take a telescope with a 9” aperture to produce the same image that a 3” scope can make in 45 min.? The VLT GranTeCan Canary Islands GMT: 7 8.4-m mirrors B. Resolving Power: Ability to make sharp images of faint objects or to distinguish between 2 adjacent objects in the sky.** aka Angular Resolution C. Atmospheric Blurring 1. Hinders ground-based scopes Ex/ “twinkling” stars 2. Best locations- high, dry, & dark Ex/ Arizona; Chile; Hawaii 3. Another solution - space. Ex/Hubble (1993) - 20 x better than previous best Pic Du Midi, French Pyrenees D. Adaptive Optics: Mirror changes shape to compensate for atmosphere. a. Lasers pierce atmosphere, create “artificial star” b. Some now sharper than Hubble! Ex/ Subaru (IR), Keck, VLT III. Radio Astronomy & Interferometry A. Radio telescopes 1. Only since the‘50’s Grote 2. Pioneers- Karl Jansky, Reber 3. Curved metal dish focuses radio waves to a focal point. 4. Instruments located at the prime focus. B. Large Size Necessary 1. Signals are faint 2. Long wavelength radio diffracts greatly - poor resolution a. Surface doesn’t have to be smooth like optical scopes b. It’s easy to make them large Ex/ Largest: Arecibo – 1000 ft. wide!(305 m) Green Bank, West Virginia - largest moveable radio dish C. Value of Radio Astronomy 1. 24 / 7 2. Thru clouds, rain, snow 3. Objects visibly dim may be strong radio sources. Ex/ *4. Radio penetrates dust in space. Ex/ Center of our galaxy D. INTERFEROMETRY 1. Interferometer: Data from 2 or more scopes combined. Ex/ VLA in N. Mex (27 dishes) ATA (2007)- 42 dishes ALMA (2012) - 66 Square Kilometer Array (2020) - 150 dishes 2. Behaves like a single dish whose diameter is the distance between dishes. Ex/ Compound eye Allen Telescope Array (so far..) Single Dish of the VLA VLA in New Mexico ALMA Largest Telescopes 2015 Refractor (lens) Yerkes Obs. 1m Single mirror GranTeCan Keck I & II Optical interferometer VLT Keck Arecibo 10.4 m 10 m 16.4 m 14.6 m 305 m Single radio dish Array (1 location) ATA (phase 1) VLA ALMA 42 dishes 27 dishes 66 dishes IV. Space Telescopes A. Microwave satellites 1. COBE (1990’s) - Measured the cosmic microwave background Proof of the Big Bang! 2. Planck (2009) B. INFRARED Astronomy 1. Long wavelength IR penetrates clouds in space. 2. Good for star or planet-forming clouds of warm dust & gas. 3. Mountaintops Ex/ Subaru 4. Airplanes Ex/ SOFIA 5. Or Space Ex/ Spitzer James Webb Space Tel. (2018) SUBARU SOFIA James Webb Space Telescope ~ 6.5 m mirror Launch in 2018 (?) Infrared C. Visible light: 1.Hubble Space Telescope 2. Spherical aberration corrected 1993 3. Final repair D. ULTRAVIOLET Astronomy 1. Used for hot stars 2. Done by high-altitude balloons 3. Or satellites Ex/ Galex, Hubble E. X-RAY Astronomy 1. No ground - only satellites 2. Used 4 violent events (black holes) 3. Special design (difficult to focus) Ex/ Chandra (1990’s) X-ray detectors F. GAMMA RAY Astronomy 1. Can’t be focused 2. Counted by special detectors 3. Scarce (~ 1 detection per day) 4. Occasional “bursts”, or GRB’s a. Hypernova – really massive star explodes / black hole formed b. Colliding binary neutron stars 5. Compton Gamma Ray Observatory (1990’s - 2000) 6. SWIFT (2004) 7. Fermi Gamma-Ray Space Telescope