jan21_10 - Announcements Next observing session tonight 6pm...

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Announcements Next observing session: tonight 6pm . Sign up beforehand (i.e. immediately after this class!). Forty spaces available at 3pm. You must sign up beforehand to have attendance counted at obs. sessions. Observing sessions next Mon., Tue.,Wed. Check Blackboard for instructions. Talking in class will be severely dealt with.
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Thursday, 21st January 2010 • Telescopes Diffraction Limit How telescopes are used: imaging, spectroscopy and timing. Effect of Atmosphere: seeing, adaptive opt. Observing at non-visible wavelengths Telescopes in Space
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6.2 Telescopes: Giant Eyes Our goals for learning: What are the two most important properties of a telescope? What are the two basic designs of telescopes? What do astronomers do with telescopes?
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What are the two most important properties of a telescope? 1. Light-collecting area: Telescopes with a larger collecting area can gather a greater amount of light in a shorter time. 2. Angular resolution: Telescopes that are larger are capable of taking images with greater detail.
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Light Collecting Area A telescope’s diameter tells us its light- collecting area: Area = × (diameter/2) 2 The largest telescopes currently in use have a diameter of about 10 meters
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Clicker Question How does the collecting area of a 10-meter telescope compare with that of a 2-meter telescope? A) It’s 5 times greater. B) It’s 10 times greater. C) It’s 25 times greater. D) It's 50 times greater E) It's 100 times greater
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Clicker Question How does the collecting area of a 10-meter telescope compare with that of a 2-meter telescope? A) It’s 5 times greater. B) It’s 10 times greater. C) It’s 25 times greater. D) It's 50 times greater E) It's 100 times greater
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Angular Resolution The minimum angular separation that the telescope can distinguish.
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Angular Resolution Ultimate limit to resolution comes from interference of light waves within a telescope. Larger telescopes are capable of greater resolution because there’s less interference
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Angular Resolution The rings in this image of a star come from interference of light wave. This limit on angular resolution is known as the diffraction limit Close-up of a star from the Hubble Space Telescope
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Ideally, with perfect optics
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Diffraction Limit for double stars Resolved Unresolved
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Angular Resolution For any telescope or interferometer, the best angular resolution possible is its diffraction limit :
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