Astronomy — Telescopes
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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