Ultraviolet explorer completes decade

Press, 23 February 1988, Page 13

Ultraviolet explorer completes decade

The International Ultraviolet Explorer satellite, known as lUE, has completed 10 years in orbit, reports the London Press Service. An astronomical satellite studying ultraviolet radiation, it was the first space observatory open to the astronomical community at large and is still operated 24 hours a day. Being parked in a geosychronous orbit above the Atlantic Ocean, lUE can be operated both from the United States and from Europe. It was controlled by the European Space Agency (ESA), the British Science and Engineering Research Council (SERC) and NASA in the United States. The mirror of the lUE telescope has a diameter of 40cm, but, in spite of its small size, continues to be one of the most productive astronomical telescopes. Used by a large number of astronomers from many countries, the telescope has led to discoveries in widely differing parts of the universe. For example, astronomers observed a newly discovered comet named IRAS and de-

tected for the first time radiation emitted by the chemical element sulphur close to a cometary nucleus. Much farther away, lUE revealed the existence of very extended hot gas in the socalled halo of our galaxy, the

Astronomers also used lUE to follow the behaviour with time of the variable radiation remitted by a remote galaxy named Fairall-9. In particular, by combining lUE observations of the variable ultraviolet radiation with ground-based observations of infrared radiation from the same object, astronomers observed how the outpouring of energetic ultraviolet light was “reprocessed” in a dusty region surrounding the compact centre of F-9 into heat radiation.

The measurement of such a small distance, equivalent to 400 light days in an extragalactic object like F-9, which is 600 million light years away, is quite a feat. Direct measurement of this distance would be far beyond other present means.