The FITS format provides a general way to encode both a definition of data and the data themselves in a machine independent form. The original definition is published in a number of articles, see Wells et al. [1], Greisen et al. [2], Grosbøl et al. [3] and Harten et al. [4]. A good general introduction to FITS can be found in [5] while a concise description is given in [6] both available through the NASA FITS Support Office and its anonymous ftp archive at Internet node nssdca.gsfc.nasa.gov.