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
The empire on which the sun never sets ring, the phrase is sometimes used critically with the implication of American imperialism, as in the title of Joseph Gerson's book, "The Sun Never Sets: Confronting the Network of Foreign U.S. Military Bases". The empire on which the sun never sets The phrase "the empire on which the sun never sets" has been used with variations to describe certain global empires that were so extensive that there was always at least one part of their territory that was in daylight. It was originally coined for the Spanish Empire, mainly in the 16th and 17th centuries. In more recent times, it