DIGITAL OPTICAL SKY SURVEYS

Cameras containing arrays of charge-coupled devices-or which are other wise capable of sustained high data rates-enable optical sky surveys t hat compete in efficiency with photographic surveys in terms of-area o f sky covered per unit observing time. There are gains in performance as well as efficiency: stellar photometry is more straightforward beca use of the higher dynamic range of CCDs, and the low noise of CCDs all ows narrow-band surveys to be undertaken. The small dead-time between exposures allows surveys for rapid variability as well as near-simulta neous color measurements. The most important new prospect may be real- time analysis for identification of sources changing either in positio n or in brightness. These gains come only after substantial investment in analysis tools and data handling and storage systems. To illustrat e some of this potential, this review will focus on a number of sky su rveys with CCDs that are either under way or in advanced implementatio n stages.