Galileo was the first to use a refracting telescope for astronomy. It is difficult to make large refracting telescopes, though, because the objective lens becomes so heavy that it is distorted by its own weight. In 1668 Newton invented a reflecting telescope. The reflector telescope uses a mirror to gather and focus light. All celestial objects are so far away that all of the light rays coming from them reach the Earth as parallel rays. Advantages: Reflector telescopes do not suffer from chromatic aberration because all wavelengths will reflect off the mirror in the same way.
Reflecting Telescopes
