03ch3Telescopes3

03ch3Telescopes3 - Ch 3 Telescopes Telescopes What they do...

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Ch 3: Telescopes Telescopes What they do Light gathering power Angular resolution Reflectors (mirrors) and Refractors (lenses) Instruments and Detectors Observatory Sites Seeing Telescopes in space Adaptive optics Interferometry
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What Telescopes do for us lescopes: magnify to reveal fine details separated by small angles collect as much light as possible to study of faint objects – near and far do both they must bring the light to a focus . Dome of the Mt Palomar 5m reflector, San Diego County.
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A large Reflector Mt Palomar 5m reflector, San Diego County.
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Light-Gathering Power Area of main opening (aperture) sets the amount of light a collected. D = diameter of the objective (primary) mirror or objective lens . The light collected depends on Area of Objective = π(D/2) 2 (p.39) A 10m telescope (D=10m) collects 16 times more light than a 2.5m. Q: What is shown below? . .How much light?
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Angular Resolution The resolution of a telescope is the angle between the closest pair of stars that barely appear as two rather than one. 1.22 (radians) resolution D λ = The resolution can not be better (smaller) than the diffraction limit of the telescope (use the same units for lambda and D): How many stars on left? perfect diffraction limited image, but we can not tell if it is a single star, or two or more unresolved stars – too close to see individually. Q: How described?
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Angular Resolution depends on Wavelength and Diameter 1.22 (radians) resolution D λ = The image of a star will have a larger diffraction limited size if we use a larger wavelength (red) or a smaller telescope The image on right is from a larger telescope or at a smaller wavelength. The image size is smaller. We like this (because can see finer details) and call it higher resolution. Q: Hubble…? Compare telescopes. .
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We want High Angular Resolution We want to see fine details: - small angles - a small value for the (angle of) resolution - we call this high angular resolution (as on the right below)
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Examples of Resolution: arc-seconds The equation for diffraction limited (best possible) resolution is: Angles are measured in degrees, arc-minutes and arc-seconds. One arcsec is about the angular size of a quarter seen 5 km away.
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This note was uploaded on 02/17/2009 for the course PHYS 7 taught by Professor Staff during the Winter '08 term at UCSD.

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03ch3Telescopes3 - Ch 3 Telescopes Telescopes What they do...

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