Photographic Sky Surveys: Days of Future Passed

Photographic surveys have played a vital role in virtually every area of astronomical research over the last 50 years. Indeed, one can make a strong case that Schmidt telescopes in general, and the Palomar 48-inch Schmidt in particular, have made the most substantial contribution to our understanding of the Universe—at least at optical wavelengths. The all-sky atlases compiled since the initiation of the POSS I O/E survey in 1949 will continue to provide fundamental reference catalogues and potent research tools for many years to come (for our children's children's children), particularly when combined with the second epoch surveys currently under way. However, as far as undertaking new, large-scale sky surveys are concerned, it is clear that we have reached the end of an era. Alternative detector technology and new instrumentation ( i.e. , CCD mosaics) can now match and, indeed, exceed the capabilities of the photographic Schmidt telescopes in undertaking effective wide-field photometric surveys. In this review, I report on the progress being made in completing the all-hemisphere photographic surveys currently being undertaken from Siding Spring with the UK Schmidt and from Palomar with the Oschin Schmidt. I also provide a summary of the availability of machine scans and/or object catalogues derived from the various surveys. Photographic survey work is not confined to these atlases, however, and section 3 provides discussion of other more specialised projects currently being undertaken. Finally, I consider the future possibilities for photographic Schmidt surveys.