f10_oct05 - Ast 307 - Tues., Oct. 5 ch. 6, Telescopes &...

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Ast 307 - Tues., Oct. 5 Light as Information Bearer By studying the spectrum of an object, we can learn its: Temperature Composition: which elements are present Velocity (radial velocity) Spectroscopy splits light into its component wavelengths. Focusing Light by Refraction To “focus” light means to bend all light rays coming from the same direction (parallel) to a single point: If the source of the light is extended, the rays come from slightly different directions, and form an image . Recording the Image An advantage of CCDs is that the data are instantly in digital form.
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Use a lens to focus the light (as the ‘primary’) Refracting telescopes need to have a long focal length to compensate for chromatic aberration The largest refractor ever built has a 40-inch diameter lens UT’s Painter Hall telescope (used for star parties) has a 9-inch diameter lens Refracting Telescopes Reflecting Telescopes Reflecting Telescopes Most research telescopes today are reflectors. Use a curved mirror to focus the light (as the ‘primary’) Reflecting telescopes can have much larger diameters because the light does not need to pass through a lens. Some have arrays of mirrors instead of a “monolithic” mirror. Multi-Element Reflecting Telescopes Twin Keck telescopes on Mauna Kea in Hawaii Segmented 10-meter mirror of a Keck telescope
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Giant Segmented Telescopes (TMTs) The next generation of telescopes will be giants: TMT stands for 20 m or 30 m telescope (left, the Giant Magellan Telescope), or even larger (the European ELT = Extremely Large Telescope). Foci of a Reflecting Telescope Newtonian focus Foci of a Reflecting Telescope The Crossley Telescope at Lick Observatory: first “big” reflector Which foci are available for use on this telescope?
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This note was uploaded on 04/30/2011 for the course AST 317 taught by Professor Dinerstein during the Fall '10 term at University of Texas.

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f10_oct05 - Ast 307 - Tues., Oct. 5 ch. 6, Telescopes &...

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