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Astronomy 1010-H Planetary Astronomy Fall_2015 Day-21
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Course Announcements How is the sunset/sunrise observing going? Dark Sky nights – Wed. 10/7 starting at 7:30pm – at the Observatory. Exam-2 will be Friday, Oct. 9; Ch. 3, 4, & 5 SW-chapter 5 posted: due Fri. Oct. 9 No lab next week – Fall Break
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The refracting telescope uses two lenses Since the eye already has a lens, the eyepiece is needed to bring the light rays back to parallel for the eye to see
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Large refractors can be very long and bulky
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The Largest Lens is 40” Built in the late 1890’s, it is the last great refracting telescope.
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Lenses and refractors suffer from Chromatic Aberration This applies to camera lenses, your eye, telescopes and anything else that uses a lens to focus light
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Correcting for Chromatic aberration can be expensive The compound lens takes two lenses of different materials and combines them to correct for color distortion
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Color separation is useful in a prism so that we can obtain a spectrum of light Since it is meant to be separated we don’t call it an aberration. Instead, it is called dispersion
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A diffraction grating works on interference of light waves Diffraction is much more efficient at separating light into its colors than dispersion
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Unfortunately, diffraction also leads to problems Look closely enough at stars and they aren’t just points of light but rings, too
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Refractors have many problems They are large and bulky and difficult to maneuver They suffer from chromatic aberration Even the best glass cuts off the IR and UV wavelengths
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Reflecting telescopes use mirrors. There are primary and secondary mirrors. Focal length is determined by the path the light takes reflecting off the mirrors.
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Reflection is the bouncing of light off a surface Mirrors do not suffer from chromatic aberration and they do not cut off long or short wavelengths
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A concave mirror focuses light to a focal point Telescope mirrors are made so that the focus is a plane instead of a point
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Reflecting Telescopes Suffer From Spherical Aberration
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There are several types of reflecting telescopes
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Definitions & Terms -1 Photon: A particle of light. Spectrum: The flux of an object as a function of wavelength.
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