The telescope is a device that intensifies and magnifies the image of distant objects. The telescope enables astronomers, scientists, and amateurs alike, to observe and study planets, stars, galaxies, and other features of the universe.

The observation of celestial objects is subjected to the limitations imposed on photons traveling over great distances, in that only a small quantity of photons will actually reach Earth. Consequently, the object appears to be faint, and because of the distance, it will also seem to be small. Therefore, the first function of the optical telescope is to intensify the light. This is done by using a lens or a mirror, or both. The larger the diameter of the objective lens, called the aperture, the more photons are captured. The world's largest optical telescope has an aperture of 236 in (6-m). Amateur astronomers will commonly use telescopes with a lens or mirror of 8 in...