Unformatted text preview: 2/22/11 Key Concepts refrac3on, reflec3on, total internal reflec3on Astro 109 Lecture 11: Op3cs and Telescopes Feb. 22 types of telescopes angular resolu3on: diffrac3on, atmospheric blurring observing at different wavelengths Feb. 22 Two principles of op3cs Reflec3on Refrac3on Refrac3on "Index of refrac3on," n, indicates how much the light bends. Light travels at a slower speed in a dense substance. Feb. 22 hJp://www.school-for-champions.com/science/waves_obstacle.htm Feb. 22 Wikipedia Thought Ques3ons If glass is clear, how can we see it? If we put one glass beaker inside another, do we see both? If so, how? Discussion Ques3on What will happen if I fill the beakers with liquid that has the same index of refrac3on as the glass? A. B. C. D. E. The two beakers will look the same as before. The inner beaker will look bigger. The inner beaker will look smaller. The inner beaker will no longer be visible. The inner beaker will break. Feb. 22 Feb. 22 1 2/22/11 Using refrac3on Feb. 22 Feb. 22 Discussion Ques3on If I move the light source up, what will happen to the image? A. The image will move up. B. The image will move down. C. The image will not move. Discussion Ques3on If I move the lens up, what will happen to the image? A. The image will move up. B. The image will move down. C. The image will not move. Feb. 22 Feb. 22 World's largest refractor Chroma3c aberra3on Feb. 22 Yerkes Observatory (Williams Bay, WI) Wikipedia Feb. 22 2 2/22/11 Reflec3on: Flat Mirror Discussion Ques3on Suppose I make a mirror curved inwards. How will it reflect light rays? A. Parallel rays will remain parallel. B. Parallel rays will be reflected toward each other. C. Parallel rays will be reflected away from each other. Wikipedia Feb. 22 Feb. 22 Reflec3on: Parabolic Mirror Reflec3ng telescope (Newtonian) Wikipedia Wikipedia Feb. 22 Feb. 22 Reflec3ng telescopes (other designs) Discussion Ques3on Reflec3ng telescopes have many advantages over refractors. Which of the following is not a true advantage? A. The primary op3cal element needs to be polished on just one side. B. A mirror can be supported all across the back. C. A reflector has no chroma3c aberra3on. D. In a refractor, some light is absorbed by the lens. E. Reflectors have more light gathering power than refractors of the same aperture. Feb. 22 Feb. 22 3 2/22/11 Gemini Observatories 8-m mirror Cassegrain design one in Hawaii, one in Chile Feb. 22 8.4-m mirror blank, fresh from the oven Feb. 22 W. M. Keck Observatory (Hawaii) Southern African Large Telescope Feb. 22 Feb. 22 Total internal reflec3on Fiber op3cs Wikipedia Feb. 22 hJp://hyperphysics.phy-astr.gsu.edu/hbase/phyopt/to3nt.html Feb. 22 Wikipedia 4 2/22/11 Diffrac3on Diffrac3on limit aperture Mainly limited by size of telescope Smallest angle that can be resolved depends on wavelength of light = 2.5 105 arcsec D
Feb. 22 Feb. 22 Again, mainly limited by size of telescope and wavelength of light. Summit of Mauna Kea, Hawaii Discussion Ques3on What is the main reason for building op3cal observatories on tall mountains? A. Land is cheap there. B. The height of the mountain puts telescopes closer to the stars. C. The thinner air allows light to travel faster. D. Mountaintops are above the turbulent lower layers of the atmosphere, allowing sharper images. E. No real reason astronomers just like mountains. Feb. 22 Feb. 22 Light pollu3on hJp://www.noao.edu/educa3on/gsmt/seeing "Twinkle, Twinkle, LiJle Star" Caused by turbulence in the atmosphere "seeing" Main limita3on of ground-based op3cal telescopes Feb. 22 Feb. 22 5 2/22/11 Adap3ve op3cs Adap3ve op3cs Deform mirror to "unblur" the image. Wikipedia Wikipedia hJp://www.astro.ucla.edu/~ghezgroup/gc/pictures/aoMovie.shtml Feb. 22 Feb. 22 Parkes Radio Telescope (Australia) Observing at non-visible wavelengths Feb. 22 Feb. 22 Green Bank Telescope (West Virginia) Arecibo Observatory (Puerto Rico) Feb. 22 Feb. 22 6 2/22/11 Radio Interferometer: Very Large Array (VLA, New Mexico) Feb. 22 Feb. 22 hJp://apod.nasa.gov/apod/ap000530.html Hubble Space Telescope Discussion Ques3on The most important reason to put an X-ray telescope in space is to Spitzer Space Telescope (IR) Chandra Telescopes in Space Fermi Gamma-ray Space Telescope A. B. C. D. E. reduce opera3ng costs. reduce construc3on costs. avoid light pollu3on. avoid absorp3on by Earth's atmosphere. avoid sunlight, since it's always night in space. X-ray XMM Feb. 22 Feb. 22 Atmospheric transparency Mul3wavelength Solar System ultraviolet op3cal infrared radio Feb. 22 Feb. 22 hJp://www.ipac.caltech.edu/Outreach/Mul3wave/gallery.html 7 ...
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- Spring '08
- Wavelength, Telescope, Refracting telescope