According to the Cambridge dictionary, a telescope is described as “a cylindrical device for making objects that are far away look nearer and larger, using a combination of lenses, or lenses and curved mirrors”.
Neat as this description may be, there are distinct types of telescopes within this which we shall examine here.
Optical telescopes collect and focus light mainly from the visible part of the electromagnetic spectrum. Using one or several optical elements such as glass, lenses or mirrors, they also gather light to affect the size and brightness of distant objects.
Instruments found in this group include theodolites, spotting scopes, monocular, binoculars, camera lenses and spyglasses. Particular telescopes found in astronomy are refracting, reflecting or catadioptric; and infrared, submillimetre and ultraviolet.
As if that wasn’t enough, telescopes can also be used to measure and observe things not discernable to the eye – for example, naturally occurring radio emissions and microwave radiation from stars, galaxies and other astronomical objects. These telescopes are called radio telescopes and are built with dishes made from conductive wire mesh to collect information.
Radio telescopes are also used to search for evidence of extraterrestrial life.
High-energy telescopes make up the final group of telescopes, and they are (unsurprisingly) used in high-energy astronomy. Objects studied in this group are those which emit EM radiation of highly energetic wavelengths: black holes, neutron stars, active galactic nuclei and supernovae. Some high-energy telescopes use mirrors while some do not focus at all and use coded aperture masks, while others still have no image-forming optical system.