Most of our information about the Universe comes to us in the form of photons. In order to understand the messages they carry with them, we must study the origins of the photons and work out their histories as they journeyed through space. By analysis of the events in which the photons participated, we can construct pictures of the diverse physical and chemical environments and processess occurring in the Universe and we can learn about the nature of the astrophysical entities in which the photons were created.

Because many of the astronomical photons are absorbed or redirected by the Earth’s atmosphere, space-based observing techniques have been developed and refined over the past several decades. The 1990’s will see the see the launch of a number of important new space astronomy missions that will produce vast amounts of high-resolution spectral data.