eso9954 — Photo Release
One Hundred Thousand Galaxies at a Glance
21 December 1999: A main scientific application of wide-angle imaging in astronomy is the census and photometric and morphological classification (i.e. by colour and shape) of large quantities of celestial objects in order to identify sources of particular interest that warrant in-depth follow-up observations. This is normally done by means of spectroscopy , a basic observing technique that allows much more comprehensive physical diagnostics than does an image. However, detailed spectral observations requires the great light-collecting power of large telescopes such as the Very Large Telescope (VLT). In the past, many important classes of astronomical objects have been discovered by such survey work. Another central goal of wide-field imaging is the identification and characterisation of structures that extend over large sky areas, e.g., of the Milky Way in which we live, of comparatively nearby galaxies, and even of the Universe as a whole. The structure of astronomical objects reveals much about their history of formation which, because of the inherently very long ("astronomical") timescales, cannot be directly observed.