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Section 1

Introduction

An archival format must be utterly portable and self-describing, on the as-

sumption that, apart from the transcription device, neither the software nor

the hardware that wrote the data will be available when the data are read.

`Preserving Scientific Data on our Physical Universe,' p. 60. Steering Com-

mittee for the Study on the Long-Term Retention of Selected Scientific and

Technical Records of the Federal Government, [US] National Research Coun-

cil, National Academy Press 1995.

This document, hereafter referred to as the `standard', describes the Flexible Image

Transport System (FITS ) which is the standard archival data format for astronomi-

cal data sets. Although FITS was originally designed for transporting image data on

magnetic tape (which accounts for the `I' and `T' in the name), the capabilities of the

FITS format have expanded to accommodate more complex data structures. The role

of FITS has also grown from simply a way to transport data between different analysis

software systems into the preferred format for data in astronomical archives, as well as

the on-line analysis format used by many software packages.

This standard is intended as a formal codification of the FITS format which has

been endorsed by the International Astronomical Union (IAU) for the interchange of

astronomical data [1]. It is fully consistent with all actions and endorsements of the

IAU FITS Working Group (IAUFWG) which was appointed by Commission 5 of the

IAU to oversee further development of the FITS format. In particular, this standard

defines the organization and content of the header and data units for all standard FITS

data structures: the primary array, the random groups structure, the image extension,

the ASCII table extension, and the binary table extension. It also specifies minimum

structural requirements and general principles governing the creation of new extensions.

For headers, it specifies the proper syntax for keyword records and defines required and

reserved keywords. For data, it specifies character and numeric value representations

and the ordering of contents within the byte stream.

FITS Standard