Introduction

The first true space observatories incorporating imaging telescopes and providing access to the soft X-ray band, but providing some overlapping response into the EUV were flown in the late 1970s and early 1980s. With the Einstein and European X-ray Astronomy Satellite (EXOSAT) satellites, launched in 1978 and 1983 respectively, long exposure times coupled with high point source sensitivity became available to high-energy astronomers for the first time. This progress depended mainly on developments in optics and detector technology but also coincided with a more sophisticated understanding of the physical processes involved in soft X-ray and EUV emission and a better appreciation of the potential significance of observations in these wavebands. This chapter describes the Einstein and EXOSAT missions detailing both the telescope and detector technology. Developments in the understanding of the physical emission processes are outlined to set the context for discussion of the most significant results from these observatories, relevant to the broad field of EUV astronomy.

Parallel developments in far-UV astronomy, arising mainly from the International Ultraviolet Explorer (IUE) observatory, provide an important complement to the work of Einstein and EXOSAT. However, since the technology of IUE is quite different to that used at shorter wavelengths we concentrate solely on the appropriate scientific results. Finally, the Voyager ultraviolet spectrometer (UVS), while mainly designed for planetary studies, was used during cruise phases of the mission, providing the first stellar EUV spectra in the region just below the Lyman limit at 912 Å.