††††A reflecting telescope collects and focuses light with a concave mirror. The first reflecting telescope was built in about 1670 by Isaac Newton. Large mirrors are cheaper to make and easier to mount than large lenses, and so all the world's really large telescopes are reflectors.
Large telescopes can now be placed in orbit above the Earth's atmosphere. Telescopes in space have been used to study radiation which does not reach the Earth but which provides much information about distant stars and galaxies. The Hubble Space Telescope, launched in 1990, can see the sky more clearly than can any telescope on Earth, since it is above the distorting effects of the Earth's atmosphere.
