This spectacular image of NGC 6946 was not made with photo- graphic techniques, but was con- structed from three images recorded on a CCD camera through red, green, and blue filters (computer processing was used to correct for variations in detector response, detector defects, and cosmic ray hits). In the early years of astronomy it was common for scientists to conduct their studies with a stack of glass photographic plates. Today, with most astronomy done electron-
ically, practitioners are more likely to carry a magnetic tape that looks like an audio cassette. One such tape can contain several daysΓÇÖ worth of data.
