Lecture08 - Lecture #8: Astronomical Instruments...

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1 Astro 102/104 1 Lecture #8: Astronomical Instruments • Astronomical Instruments: – Optics: Lenses and Mirrors. – Detectors. – Ground Based Telescopes: • Optical, Infrared, and Radio. – Space Based Telescopes. – Spacecraft Missions. Astro 102/104 3 The Main Point Astronomers are constantly trying to maximize the resolution of their observations, but there are fundamental limits because of wavelength, telescope size, and the blurring effects of our atmosphere. Astro 102/104 4 Some Basics • Astronomers rely on instruments that collect , magnify, and/or disperse light. • How much light can be collected is determined by the aperture of the collecting instrument. • A combination of lenses or mirrors are used to focus light onto a detector. • Dispersion is obtained using a prism or grating. • Detectors include photographic plates, photo- sensitive resistors, and silicon semiconductors. Astro 102/104 5 Familiar Optics • Telescopes operate on the same principles as your eyes.
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2 Astro 102/104 6 Resolution Spatial Resolution is a measure of the smallest details that can be identified by an instrument. • Resolution is limited by: Diffraction of light by lenses and mirrors: • Depends on the wavelength. • Depends on the aperture or diameter of the instrument. –The "seeing" or amount of turbulence in the atmosphere. • Resolution typically expressed in arcseconds: – 1° = 60 arcminutes = 3600 arcseconds (3600"). – Typical human resolution: ~ 60" (~1/60°). Astro 102/104 7 Resolution: Theory •T h e diffraction limit of any optical instrument is: θ ~ 2.5x10 5 ( λ / D), where θ = the best possible resolution, in arcseconds. λ = the wavelength of the observation. • D = the diameter of the instrument's aperture. –Examp le s • Best resolution of the Hubble Space Telescope at 500 nm? θ ~ 2.5x10 5 ( 500x10 -9 m / 2.4 m) = 0.05" • What size telescope needed to obtain θ = 0.001" at 500 nm? – D ~ 2.5x10 5 ( λ / θ ) = 2.5x10 5 (500x10 -9 m / 0.001) = 125 m (!) } must be in the same units Astro 102/104
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This note was uploaded on 03/04/2008 for the course ASTRO 1102 taught by Professor Squyres,s/margot,j during the Spring '07 term at Cornell University (Engineering School).

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Lecture08 - Lecture #8: Astronomical Instruments...

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