Home > Encyclopedia of Science > Telescope

• Words to Know
• Refractor telescopes
• Reflector telescopes
• Limits to ground-based telescopes
• Space-based telescopes
• The future on the ground

The telescope is an instrument that gathers light or some other form of electromagnetic radiation (from radio waves to gamma rays) emitted by distant sources. The most common type is the optical telescope, which uses a collection of lenses or mirrors to magnify the visible light emitted by a distant object. There are two basic types of optical telescopes—the refractor and the reflector. The one characteristic all telescopes have in common is the ability to make distant objects appear to be closer.

The first optical telescope was...