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Light and Telescopes

0. Light and Telescopes. Chapter 5. 0. Traditional Telescopes. The 4-m Mayall Telescope at Kitt Peak National Observatory (Arizona). 0. Advances in Modern Telescope Design (I). Modern computer technology has made possible significant advances in telescope design:.

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Light and Telescopes

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  1. 0 Light and Telescopes Chapter 5

  2. 0 Traditional Telescopes The 4-m Mayall Telescope at Kitt Peak National Observatory (Arizona)

  3. 0 Advances in Modern Telescope Design (I) Modern computer technology has made possible significant advances in telescope design: 1. Simpler, stronger mountings (“Alt-azimuth mountings”) to be controlled by computers

  4. 0 Advances in Modern Telescope Design (II) 2. Lighter mirrors with lighter support structures, to be controlled dynamically by computers. Floppy mirror Segmented mirror

  5. 0 The Keck Telescopes The two Keck Telescopes on Mauna Kea, Hawaii. Each telescope has a mirror diameter of 10 meters.

  6. 0 Examples of Modern Telescope Design The Large Binocular Telescope (LBT) The Very Lage Telescope (VLT) in Chile

  7. 0 The Future of Optical Telescopes The Giant Magellan Telescope (2016) The European Extremely Large Telescope (E-ELT): 906 segments in a 42-m mirror!

  8. 0 Adaptive Optics Computer-controlled mirror support adjusts the mirror surface (many times per second) to compensate for distortions by atmospheric turbulence. Distortions by the atmospheric turbulence are measured using a laser beam.

  9. 0 Interferometry Recall: Resolving power of a telescope depends on diameter D: amin = 1.22 l/D. This holds true even if the entire surface is not filled out. → Combine the signals from several smaller telescopes to simulate one big mirror →Interferometry

  10. What a telescope does • Typical resolution of eye is about 0.5 minutes of arc or 30 arc seconds. • HST has a resolution of 11.6/240 = .048 arc seconds. With HST we can resolve objects that are almost 1000 times smaller. • NOTE the equation used above was given on page 77 of the textbook.

  11. 0 CCD Imaging CCD = Charge-coupled device • More sensitive than photographic plates • Data can be read directly into computer memory, allowing easy electronic manipulations False-color image to visualize brightness contours

  12. 0 Negative Images The galaxy NGC 891 as it would look to our eyes (i.e., in real colors and brightness) Negative images (sky = white; stars = black) are used to enhance contrasts.

  13. 0 The Spectrograph Using a prism (or a grating), light can be split up into different wavelengths (colors!) to produce a spectrum. Spectral lines in a spectrum tell us about the chemical composition and other properties of the observed object.

  14. 0 Radio Telescopes Large dish focuses the energy of radio waves onto a small receiver (antenna). Amplified signals are stored in computers and converted into images, spectra, etc.

  15. 0 Radio Maps In radio maps, the intensity of the radiation is color-coded: Red = high intensity; Violet = low intensity Just like optical telescopes, radio telescopes should be built in regions with low average rainfall and cloud cover, and low radio noise.

  16. 0 Radio Interferometry Just as for optical telescopes, the resolving power of a radio telescope is amin = 1.22 l/D. For radio telescopes, this is a big problem: Radio waves are much longer than visible light. The Very Large Array (VLA): 27 dishes are combined to simulate a large dish of 36 km in diameter. →Use interferometry to improve resolution!

  17. 0 The Largest Radio Telescopes The 100-m Green Bank Telescope in Green Bank, WVa. The 300-m telescope in Arecibo, Puerto Rico.

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