The telescope is an instrument that collects and analyzes the radiation emitted by distant sources. The most common type is the optical telescope, a collection of lenses and/or mirrors that is used to allow the viewer to see distant objects more clearly by magnifying them or to increase the effective brightness of a faint object. In a broader sense, telescopes can operate at most frequencies of the electromagnetic spectrum, from radio waves to gamma rays. The one characteristic all telescopes have in common is the ability to make distant objects appear to be closer (from the Greek tele meaning far, and skopein meaning to view).

The first optical telescope was probably constructed by the Dutch lens-grinder, Hans Lippershey, in 1608. The following year, Galileo Galilei built the first astronomical telescope from a tube containing two lenses of different focal lengths aligned on a single axis (the elements of...