The sheer durability of IUE enabled astronomers to revisit many objects over nearly two decades and to see changes occurring with them. The prolonged study of the black hole in 3C3903.3 was a case in point. Another conspicuous example of the advantages of a long life concerns Supernova 1987A. This star was seen exploding in a nearby galaxy, the Large Magellanic Cloud, halfway through IUE's operational life.

Black hole accretion disk in Galaxy 3C390.3. Diagram (not to scale) on X-ray and radio images from Harris et al. (ApJ. 499, L149) and 1452 Mhz VLA.

Comets

The return of Halley's comet in 1985-1986 was a long-anticipated event, and the ultraviolet observations by IUE measured the rate at which the famous object spewed water vapour into space. But many comets appear unexpectedly, and IUE was able to examine them too, from Comet Seargent in 1978 to Comet Hale-Bopp in 1986. Astronomers have built up a comprehensive picture of comets seen by ultraviolet light at different stages of their evolution, and at different distances from the Sun. As a result, they have a much better understanding of how comets react and change during their rare visits to the vicinity of the Sun and the Earth.

IUE's long life also enabled it to observe rare and serendipitous events. The satellite was already more than sixteen years old when Comet Shoemaker-Levy 9 hit Jupiter in July 1994. The event was well anticipated, so IUE was able first to study Jupiter in a normal state, and then to see the changes in the ultraviolet spectra during and after the impacts of the comet fragments.

	UV Spectroscopy
	Astronomers Favourite