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
Day of the Sun leaders. Festivities are not confined to the date. Commemorations occur from 16 February, which is the birthday of Kim Jong-il, during what is known as the Loyalty Festival. Celebrations in April around the Day of the Sun are called the Sun Festival. The day itself is followed by two days of rest, making it a three-day holiday. Kim Il-sung was born on 15 April 1912 in the village of Mangyongdae, which is now a suburb of North Korea's capital Pyongyang. He has been long identified with the Sun and is frequently called "Sun of the nation". He adopted his name