Astronomical telescope A telescope used to study objects in space. Astronomical telescopes include optical telescopes, radio telescopes and space telescopes.

Binoculars A pair of telescopes fixed side by side, with one telescope for each eye. Binoculars can magnify objects to look up to 20 times their size.

Catadioptric telescope A telescope that combines lenses and mirrors to minimize image distortions. The most famous type are Schmidt-Cassegrain telescopes, which were invented in 1940.

Cassegrain-type telescope A reflecting telescope that uses two mirrors. Light is focused by a large primary mirror on to a smaller secondary mirror. From there it reflects to the viewer or light sensor.

Galileo Galilei (1564-1642) Italian astronomer who, in 1609, used the first astronomical telescope, with which he discovered four moons around Jupiter.

Gran Telescopio Canarias (GranTeCan) The world’s largest telescope, positioned atop a 2400-metre (7900-foot) peak on an island in the Canaries. Its mirror, measuring 10.4 metres (34.1 feet) across, consists of 36 hexagonal segments fitted in a honeycomb pattern.

Hubble Space Telescope A reflecting space telescope that orbits Earth. Hubble can detect visible light, infrared and ultraviolet rays. It can see 10 times more detail than Earth-based telescope and objects 50 times as faint. Solar panels provide its power and images are transmitted back to Earth by radio.

Interferometry A technique that combines results from several telescopes to increase their resolution. If two telescopes are placed 50 metres (160 feet) apart, their combined power will be the same as a telescope 50 metres across. Interferometry is used because it is cheaper to erect several small telescopes than to build one large one.

James Webb Space Telescope The successor to the Hubble Space Telescope, the James Webb Space Telescope (JWST) orbits the Sun around 1.5 million kilometres (940,000 miles) from Earth. Launched on 25th December 2021, the JWST is fitted with a 6.5-metre primary mirror made up of 18 hexagonal mirror segments. The telescope, which is much bigger and more powerful than the Hubble, will mainly be used to detect infrared radiation and will focus on distant galaxies and exoplanets.

Lippershey, Hans (1570–1619) German-Dutch lens-maker who is thought to have made the first telescope in 1608.

Observatory A building where a telescope is housed. Observatories are usually sited on mountaintops where light and air pollution is at a minimum and where viewing is least affected by cloudy skies or atmospheric disturbance.

Optical telescope A telescope that collects light coming from distant objects and uses it to produce images of the objects. The two main types of optical telescope are refracting and reflecting telescopes.

Radio astronomy A branch of astronomy based on the study of radio waves given off by objects in space. Many celestial objects, such as stars and galaxies, emit radio waves and other sorts of radiation as well as light. Radio astronomy has led to the discovery of new celestial objects, such as pulsars, that would be otherwise invisible.

Radio telescope A telescope that collects radio waves given off by celestial objects, such as stars. A radio telescope has a large dish that collects radio waves and focuses them on to a receiver. It can be turned to collect rays from any part of the sky.

Reflecting telescope An optical telescope that uses a concave (dish-shaped) mirror to collect light from an object and focus it to form an image. Larger telescopes are usually reflecting telescopes because mirrors are lighter than lenses and more compact than refracting telescopes.

Refracting telescope An optical telescope that uses a convex (bulging) lens to collect light from an object and focus it to form an image. The larger the lens, the more distant the objects that can be observed and the brighter their image will be.

Space telescope A telescope in space, used to study radiation that is blocked by Earth’s atmosphere. Space telescopes use special mirrors to reflect radiation, and electronic detectors to record images. Optical telescopes also work better in space as they are unaffected by the atmosphere. All ground-based telescopes are affected by the atmosphere, which distorts light rays as they pass through it.

Telescope An instrument that makes distant objects appear closer, allowing the viewer to see details that are not visible with the naked eye. Objects on Earth and in space can be observed using optical telescopes, which collect light from distant objects and use it to produce images. They can also be observed using radio telescopes, which gather other forms of radiation besides light, such as radio waves, infrared rays, X-rays and gamma rays. The development of telescopes has helped mankind to make many discoveries about the Universe.

Terrestrial telescope An optical telescope used for viewing objects on Earth.

Consultant: Chris Oxlade