The word telescope was coined at a banquet for Galileo in 1611
Galileo called his instrument a perspicillum. The name that stuck came in 1611 from Giovanni Demisiani, a mathematician of Greek origin, who proposed it at a banquet of Rome's Accademia dei Lincei where one of Galileo's devices was shown off. Built from Greek words for far and see, telescope means far-seeing.
The earliest record of a telescope is a 1608 patent application in the Netherlands by Hans Lipperhey, a spectacle maker from Middelburg, though who really invented it remains unknown. News travelled fast, and in 1609 Galileo built his own and turned it on the sky. Within a few decades others were building telescopes that gathered light with curved mirrors instead of lenses, and Isaac Newton made the first practical one in 1668. Much later, in 1956, John Dobson devised the simple, cheap mount that bears his name.
Both kinds had problems. Simple lenses smeared colours until the achromatic lens of 1733 helped fix them. Mirrors of speculum metal tarnished quickly, a problem eased by silver-coated glass in 1857 and aluminium coatings in 1932. Lenses cannot usefully be made much wider than about a metre, so nearly every large research telescope built since around 1900 has been a reflector. The biggest now have mirrors over 10 metres across, and designs of 30 to 40 metres are underway.
Today telescope means any instrument that collects radiation from distant objects, from radio waves, first studied with a purpose-built radio telescope in 1937, to infrared, pursued from the 1960s, and gamma rays. Earth's atmosphere blocks most of the spectrum, letting through only visible light, some near-infrared and part of the radio band. X-ray and far-infrared telescopes must therefore fly in orbit.
Space also escapes clouds, atmospheric shimmer and light pollution, at the price of cost, size limits and difficult repairs. NASA's Hubble covers ultraviolet to near-infrared, Kepler found thousands of planets around other stars, and the infrared James Webb Space Telescope launched on 25 December 2021 from French Guiana to orbit a point beyond the Moon called L2.
Source: Telescope
