1.1 The Need for FITS

In the late 1970s, the Westerbork Synthesis Radio Telescope (WSRT) in Westerbork, Holland and the Very Large Array (VLA) in New Mexico began producing high quality images of the radio sky. Since the two groups were observing at different frequencies, they wished to collaborate in constructing spectral index maps by combining data obtained from the two instruments. It was clear from the outset that this process would not be trivial. Two different institutions would normally structure their data in different ways. Machines at the two different installations might have different architecture, using a different internal representation for the same number. Lacking a standard format for transporting images, an astronomer taking data from an observatory to a home institution would have to create special software to convert the data to the format used at the home institution. Such software would restructure the data to the format of the home institution and perform whatever bit manipulations were necessary to convert numbers from the representation in the originating machine to that for the destination machine.

While radio astronomers were making great strides towards producing analog images of their normally digital data, optical astronomers were making great strides toward producing high quality digital data through the use of charge coupled devices (CCDs). Here too, transport of data in one wavelength domain for comparison with data in another wavelength domain was required. Because each installation had its own internal storage format, new software was needed whenever two installations exchanged data for the first time.

An obvious substitute for all these cumbersome processes was the creation of a single standard interchange format for transporting digital images among cooperating institutions. Then, each institution would need only two software packages: one to translate the transfer format to the internal format used by the institution, and one to transform the internal format to the transfer format. The Flexible Image Transport System (FITS) was created to provide such a transfer format.

From its initial applications--exchange of radio astronomy images between Westerbork and the VLA and exchange of optical image data among Kitt Peak, the VLA and Westerbork--the use of FITS has expanded to include the entire spectrum of astronomical data. It is being used for a variety of data structures from past, current and future NASA-supported projects, for example, X-ray data from the Einstein High Energy Astrophysics Observatory (HEAO-2), the Compton Gamma Ray Observatory, and the Röntgen Satellite (ROSAT) where NASA is cooperating with Germany and the United Kingdom; ultraviolet and visible from the International Ultraviolet Explorer (IUE) and the Hubble Space Telescope; and infrared data from the Infrared Astronomical Satellite (IRAS) and the Cosmic Background Explorer (COBE). It is also the standard for ground-based radio and optical observations, in use by such organizations as the National Radio Astronomy Observatory (NRAO), National Optical Astronomy Observatories (NOAO), and the European Southern Observatory (ESO).