All these forms of electromagnetic radiation are emitted as waves. Rapid advances in astrophysics and optical technology, coupled with the advent of the space age, broadened telescope technology in the last quarter of the 20 th century. Astronomical telescopes today come in a wide variety of shapes and sizes, dictated largely by the portion of the electromagnetic spectrum the telescope is designed to view. Telescopes today view the entire spectrum of electromagnetic radiation sweeping the universe. Each new advance in wavelength coverage has dramatically altered our view of the universe.
Many telescopes are Earth-based, located in astronomical observatories around the world.
But only radio waves, visible light, and some infrared radiation can penetrate Earth's atmosphere and reach the surface of our planet. To overcome this problem, scientists have launched telescopes into space, where the instruments can collect waves from the other regions of the electromagnetic spectrum . There are two main kinds of optical telescopes refracting and reflecting. A Refracting Telescopes Refracting telescopes, or refractors, use a glass lens to bend, or refract, starlight and bring it to a focus. The lens is convex, meaning that the center of the lens is its thickest part, and the lens becomes thinner toward its edges.