GNU Astronomy Utilities

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5.1 Header

The FITS standard requires each extension of a FITS file to have a header, giving basic information about what is in that extension. Each line in the header is for one keyword, specifying its name, value and a short comment string. Besides the basic information, the headers also contain vital information about the data, how they were processed, the instrument specifications that took the image and also the World Coordinate System that is used to translate pixel coordinates to sky or spectrum coordinates on the image or table.