History of the telescope of the IRAS satellite in 1983 revolutionized infrared astronomy from space. This reflecting telescope which had a mirror, operated for nine months until its supply of coolant (liquid helium) ran out. It surveyed the entire sky detecting 245,000 infrared sources—more than 100 times the number previously known. Although optical telescopes can image the near ultraviolet, the ozone layer in the stratosphere absorbs ultraviolet radiation shorter than 300 nm so most ultra-violet astronomy is conducted with satellites. Ultraviolet telescopes resemble optical telescopes, but conventional aluminium-coated mirrors cannot be used and alternative coatings such as magnesium fluoride or lithium fluoride are used
Ultraviolet photography and it allows only the radiation to pass which is needed to induce a particular fluorescence. As before, a barrier filter must also be placed in front of the camera lens to exclude undesired wavelengths. Ultraviolet photography was used as evidence in court at least as early as 1934. Photographs made with ultraviolet radiation can reveal bruises or scars not visible on the surface of the skin, in some cases long after visible healing has completed. These can serve as evidence of assault. Ultraviolet imaging can be used to detect alteration of documents. Ultraviolet photography Ultraviolet photography is a photographic