Textbook Notes (363,693)
Physics (160)
PHYS 183 (51)
Tracy Webb (12)
Chapter 6

# Chapter 6

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School
Department
Physics
Course
PHYS 183
Professor
Tracy Webb
Semester
Winter

Description
6: Telescopes 6.2 Telescopes: Giant Eyes  2 main properties of telescopes: o light of collecting area: tells us how much total light telescope can collect at one time  characterize telescope’s size as diameter of light-collecting area (since lens is round) o angular resolution: smallest angle over which we can tell that two dots/stars are distinct  human eye has angular resolution of 1 archminute, so must have that must angular separation in sky for us to tell they are 2 stars, not 1  dependent on actually separation & distance from us  ultimate limit of telescope  properties of light o since light is an electromagnetic wave, can interfere with one another like ripples  interference limits telescope’s angular resolution  diffraction limit: angular resolution a telescope could achieve if it were limited only by interference of light waves  depends on diameter of primary mirror & wavelength of light  refracting telescope: operates like an eye, using transparent glass lenses to collect & focus light  reflecting telescope: uses precisely curved primary mirror to gather light & reflects it onto a secondary mirror which reflects the light to a focus at a place where the eye can observe it  nearly all in current research are reflecting telescopes o light passes through lens of refracting telescope so it must be made from clear, high- quality glass with precisely shaped surfaces on both sides  reflecting surface of mirror must be precisely shaped, not both sides o difficult to stabilize refracting telescopes & prevent large lenses from deforming  primary mirror of reflecting at bottom so weight less serious problem  observations through telescopes fall into 3 categories o imaging  photographs or astronomical objects  may place filters in front to allow particular colours/wavelengths  most images of astronomy are combined images of different filters  today many images made from invisible light (anything other than visible light)  no natural colour since colour is a property of visible light o spectroscopy  obtain & study spectra  spectrographs: use diffraction grating to separate various colours of light into spectra  information from image depends on angular resolution & spectral resolution  requires longer exposure time than taking an image o timing  tracks how object changes with time  results often shown as light curves  light curves: graphs that show how an object’s intensity varies with time 6.3 Telescopes and the Atmosphere  telescopes on the ground are less expensive to build, operate & maintain than telescopes in space  problems with observing from earth  daylight, weather, light pollution, blurry images by atmospheric motion, light not reaching ground  daylight  daytime sky brighter since atmosphere scatters sunlight which drowns dim light of most astronomical objects  light pollution  lights of cities scattered at night making it hard to see light of astronomical objects o placing reflective covers on tops of streetlights directs more light toward ground o low pressure lights can only be seen in a few wavelengths, so can be fi
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