Lec 8: 2 FEB 2012 ASTR 130 - Introductory Astronomy II (Chapter 6) LAST TIME - Optics and Telescopes Basic Functions of a Telescope Reflecting v. Refracting Affects of the Atmosphere TODAY Modern Astronomical Observatories Overcoming Limitations of the Atmosphere Multiwavelength Astronomy Telescopes and Observatories TUESDAY - The Sun as a Star (Read Chapter 16) Exam 1 (Chap 5, 6, 16) - Thursday, 9 FEB Seeing Through the Atmosphere Reflection some of starlight reflected back to space some artificial light reflected back down ( light pollution ) Absorption UV, X-ray, γ-ray completely absorbed IR mostly blocked water vapor and oxygen absorption lines Emission sky glow aurorae Transmission close to 100% for visible and radio, but... haze, dust, water vapor, etc. decrease this seeing : blurring, twinkling, distortion WEATHER!! Light Pollution Atmospheric Absorption of Light Earth s atmosphere absorbs most types of light. good thing it does, or we would be dead! Only visible, radio, and certain IR and UV light make it through to the ground. To observe the other wavelengths, we must put our telescopes in space! Atmospheric Seeing point image of star fuzzes out to ~1 arc-sec image bounces around even a 4 telescope is limited by seeing mountain tops have much better seeing how do we try to overcome this limitation? Speckle Imaging: real short exposures; shift positions; stack images Active Optics: tip and tilt the mirror quickly to respond to twinkling Adaptive Optics: warp shape of mirror quickly to compensate for atmospheric distortion Interferometry: combine light from widely-spaced telescopes to simultate large aperture 1
Adaptive Optics (AO) Active Optics Support for Large Primary Mirror By monitoring the distortions of the light from a nearby bright star (or a laser): a computer can deform the secondary mirror in the opposite way. the wavefronts, when reflected, are restored to their original state. AO mirror off AO mirror on Angular resolution improves. These two stars are separated by 0.38ʺ Without AO, we see only one star. Kitt Peak National Observatory Cerro Tololo Interamerican Observatory Mauna Kea La Silla, European Southern Observatory 2
Radio Telescopes The wavelengths of radio waves are long. So the dishes which reflect them must be very large to achieve any reasonable angular resolution. 305-meter radio telescope at Arecibo, Puerto Rico Optical and Radio Views of Saturn Two (or more) radio dishes observe the same object. Their signals are made to interfere with each other. An image is reconstructed with the angular resolution one would get from a dish the size of the distance between them. The light-collecting area is still only the sum of the areas of the individual dishes. Interferometry The VLA (Very Large Array) The VLBA (very large baseline array) 3
The Keck 10 meter Telescopes VLT Interferometric Array Astronomy at the South Pole Station Space Based Telescopes Chandra X-ray Obs. Hubble Space Telescope Observing All Wavelengths of EMR x-rays and gamma-rays produced in most violent events; highest energies penetrate anything, but lower energies easily stopped by our atmosphere stars produce most of their light in ultraviolet and visible; star s color is an indirect indicator of its properties (e.g. mass, age) infrared and radio waves penetrate through clouds, which allows us to see through material that is opaque to visual light and study what is on other side or embedded each new window on the universe can lead to surprising new discoveries Visible Light most of the light comes from nearby stars Orion nebula is just a fuzzy patch of light Infrared Light light penetrates the interstellar clouds in the star forming region; allows us to study birth of stars! 4
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