This restricts astronomy on Earth’s surface to the near ultraviolet, visible, and radio regions of the electromagnetic spectrum and to some relatively narrow “windows” in the nearer infrared.Longer infrared wavelengths are strongly absorbed by atmospheric water vapour and carbon dioxide.Also, major photographic surveys, such as those of the National Geographic Society and the Palomar Observatory, can provide a historical base for long-term studies.
Gamma rays are detectable through their Compton scattering, electron-positron pair production, or Cerenkov radiation.
The angular resolving power (or resolution) of a telescope is the smallest angle between close objects that can be seen clearly to be separate. For a telescope having an objective lens or mirror with diameter resolving powers; in practice, however, these are not attained for telescopes located on Earth’s surface, because atmospheric effects limit the practical resolution to about one arc second.
Sophisticated computing programs can allow much-improved resolution, and the performance of telescopes on Earth can be improved through the use of adaptive optics, in which the surface of the mirror is adjusted rapidly to compensate for atmospheric turbulence that would otherwise distort the image.
In another technique, called Earth is a moving platform for astronomical observations.
It is important that the specification of precise celestial coordinates be made in ways that correct for telescope location, the position of Earth in its orbit around the Sun, and the epoch of observation, since Earth’s axis of rotation moves slowly over the years.
These distort under their own weight and can be supported only around the perimeter; an appreciable amount of light is lost due to absorption in the glass.