Telescope Aperture

The aperture of a telescope is several times larger than the aperture of the human eye, so that the objects that cannot be normally seen by the unaided eye can be seen. 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 centimeter diameter telescope collects four times more photos than a 10 centimeter 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. A long 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 superior resolution, the ability to discern fine detail. Small resolution is good. The resolution is directly proportional to the wavelength being observed and inversely proportional to the diameter of the telescope.