Telescope

The aperture of a telescope is several times larger than the aperture of the human eye so that the objects that can not be normally seen by unaided eye can be seen. The light-gathering power of a telescope is proportional to the area of its aperture and hence depends on the square of the radius of the mirror. Therefore, a 20 cm diameter telescope collects four times more photons than a 10 cm diameter telescope. A telescope can be equipped to record light over a long period of time, by using photographic film or electronic detectors such as photometers or CCD detectors while the eye has no capability to store light. Along-exposure photograph taken through a telescope reveals objects too faint to be seen with the eye, even by looking through the same telescope. A third major advantage of large telescopes is that they have a superior resolution, the ability to discern fine detail. A small resolution is good. The resolution is directly proportional to the wavelength being observed and inversely proportional to the diameter of the telescope.