Ultraviolet sky surveys. Instruments, findings, and prospects

I review the development of UV and EUV astronomy, covering the spectral range from 5 to 300 nm, with emphasis on sky surveys for discrete sources. I discuss studies which resulted in lists of sources observed by imaging and deliberately omit most spectroscopic studies. Technical issues, such as detector and telescope developments, are treated separately from descriptions of specific missions and their results, which contributed to the understanding of the UV sky. The missions are compared in terms of their 'survey power', a variable which combines sky coverage and survey depth. I use the existing knowledge of UV sources to predict views of the UV sky, which I then compare with those actually detected. Finally, UV missions which will detect fainter sources and will fly in the near future are described, and a wish list for low-cost ventures, which could considerably advance our knowledge of the UV sky, is presented.