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The event of the century for astronomers was the cataclysmic explosion of a massive star. Although such supernovae are crucial in cosmic history, and the source of the Earth's gold and uranium, none had been seen at close range with modern instruments. Stargazers spotted Supernova 1987A in February 1987, in the Large Magellanic Cloud in the southern sky. When the news broke, the very first space telescope to turn towards Supernova 1987A was the astronomical satellite IUE.
As the supernova faded rapidly in the ultraviolet, IUE's experts could say, years before other observers, exactly which star blew up. It was a blue star, not red as expected. The satellite registered ultraviolet signatures of newly-made chemical elements released by the explosion.
The flash lit up a distant ring of gas surrounding the star, and IUE recorded an echo of the light, a month after the explosion. In 1990 the Hubble Space Telescope began examining the scene. The European Space Agency's Faint Object Camera on Hubble detected a cloud of debris and measured its expansion rate. It also imaged the ring of gas responsible for IUE's echo from the supernova. Later, NASA's wide-field cameras examined the ring, which is the central orange coloured ring in the accompanying image.
"From IUE's light echo and the ring measured with Hubble, we could tell how far away the supernova was," said Nino Panagia, an ESA scientist from Italy working at the Space Telescope Science Institute. "In 1991 we put Supernova 1987A at a distance of 167 000 light-years. With better pictures we confirmed that result, and reduced the uncertainty to as little as two percent."
In 1993 a supernova event occurred in the relatively near galaxy M81, in the constellation of Ursa Major, and just 24 hours after its discovery the IUE spacecraft made a spectrum of its ultraviolet light (central band). Converting it into a graph of energy (in white) astronomers judged from the overall shape of the spectrum that gas around the exploding star was radiating at a temperature of 22 500 degrees. The tall spike at the left-hand end came from nitrogen atoms heated to about one billion degrees by a shock wave from the supernova.