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astronomytelescopes ( ** )

Astronomy — Telescopes


  • 7 x 50 power for a set of binoculars means magnification of 7 and an objective lens of 50 mm.  Magnification for binoculars = diameter of the objective lens divided by the diameter of the eyepiece.  M = D.O. / D.E.
  • Telescopes aid our eyes in three ways:  1) light-gathering power  [the bigger the better]  2) resolving power [the bigger the better]  3) magnification.
  • For telescopes, the magnification = focal length of the objective lens divided by the focal length of the eyepiece.
  • Ground-based telescopes can only operate in optical and radio wavelength windows.
  • When light is reflected through glass, shorter wavelengths (blue) are bent more than longer wavelengths (red), thus we get chromatic aberration.
  • The great the focal length of the objective, the greater the magnification.
  • f/4 = low power view of a large area;  f/6-8 = general observing;  f/10-15 = narrow high-power field.
  • Radio telescopes have three handicaps:  1) poor resolution  2) radio waves are of low intensity  3) interference.
  • The resolution of a radio telescope can be greatly improved by linking radio telescopes great distances apart.
  • Radio telescopes can detect cool hydrogen clouds in space, since they emit a radio signal at 21 cm wavelength.
  • Light-gathering power is proportional to the area of the telescope objective.  A lens or mirror with a large area gathers a large amount of light.  Comparing a 5-cm telescope to a 25-cm telescope, the larger scope has 25-times the light-gathering power.
  • The magnification of a telescope is the ratio of the focal length of the objective lens or mirror divided by the focal length of the eyepiece.

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