Single Dish Radio Telescopes

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Comparison of Optical and Radio Telescopes

Visible (optical) light is merely one part of the electromagnetic spectrum. Telescopes for other parts of the EM spectrum are possible.

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  • For a range of frequencies, reflecting primary mirrors are used to direct EM radiation to a focal point.
  • Some radio telescopes, along with optical telescopes, are steerable (able to be steered).
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  • Because of the range of frequencies, the scale of radio telescopes is considerably larger than those of optical telescopes.
  • For a range of frequencies, dipole and other arrangements with considerable designs are preferable for radio telescopes.
  • The scale and design of some radio telescopes make them unsteerable.
    • Large radio telescopes, such as those at Arecibo, Costa Rica, rely on the rotation of the Earth to point them at different regions of the sky.

Resolution and Collecting Power

Visible (optical) light is merely one part of the electromagnetic spectrum. Telescopes for other parts of the EM spectrum are possible.

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  • The resolution of a telescope is defined as the smallest separation between two objects in the sky that the telescope can discern (tell apart).
  • The resolution is directly proportional to the ratio:
    • (wavelength of radiation) / (diameter of the aperture of the telescope).
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Resolution comparison

  • For radio telescopes, because the wavelengths involved are very large compared with the diameters of the dishes required, the resolving power is low.
  • For optical telescopes, the wavelength is much smaller than the telescope aperture (i.e. the primary mirror) so optical telescopes can tell two sources apart that are much closer together than can be achieved with radio telescopes.
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Collecting power

  • Collecting power is defined as a measure of the intensity of the EM radiation that can be gathered by a telescope.
  • The collecting power is directly proportional to the square of the diameter of the primary mirror.
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Collecting power 2

  • Generally, radio telescopes have much larger diameters, which means that their collecting powers are higher.
  • But radio sources are generally significantly less intense than sources of optical light.

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