Looking back

The astrophysical research discipline we now know as Extreme Ultraviolet astronomy is approximately 30 years old. An observational technique once dismissed as impossible has become established as a significant branch of space astronomy and a major contributor to our knowledge of the Universe. In several areas, the science obtained from EUV observations is unique. For example, the presence of the He II Lyman series in this spectral range provides a diagnostic tool for the study of the second most abundant element in the Universe in the atmospheres of hot stars and in interstellar space. The determination of the ionisation fraction of helium in the local ISM could not have been carried out in any other spectral range.

EUV astronomy has passed through the development phases that might be deemed typical of a discipline depending on access to space. Beginning with the sounding rocket borne experiments of the early 1970s, the longer duration Apollo–Soyuz Test Project highlighted the potential of the field, with the first reported source detections in 1975. However, it was a further 15 years before the next major advance with the first EUV all-sky survey of the ROSAT WFC (in 1990) followed by the wider spectral coverage of the EUVE survey in 1992. The underlying reasons for this hiatus had more to do with national and international politics, together with the economics of funding opportunities and even the launch delays following the Challenger disaster, than technological limitations.