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FITS Standard Document

The official reference document that defines the requirements for FITS format data files.


Version 4.0 [DRAFT]     (22 July 2016):    PDF format,   

This is a draft of the next version of the FITS Standard document that includes descriptions of all the new features that have been officially added to the FITS format since the publication of Version 3.0 of the document. The 8 new features are summarized in appendix H.3 of the document:
  1. Conventions for representing Time world coordinates
  2. The CONTINUE keyword for representing long string keyword values over multiple header records
  3. A convention for preallocating scratch space in a FITS header which is then available for future use when appending new keywords to the header
  4. The INHERIT keyword to indicate whether or not the current extension should inherit the keywords in the primary header
  5. The CHECKSUM and DATASUM keywords for verifying the veracity of the contents of the file
  6. The TLMINn and TLMAXn keywords for specifying the minimum and maximum values in table columns
  7. The Green Bank convention for expanding header keywords into table column entries when the value varies row-by-row
  8. Conventions for compressing FITS images and tables
The full release of this document is expected later in 2016, pending possible minor editorial corrections to the text.

Version 3.0 (July 2008):
Published version:     in Astronomy and Astrophysics, Volume 524 (December 2010)

Latest PDF document maintained by the IAU FITS Working Group (November 2010)

Other related documents:


Version 2.1b (December 2005):    PDF format,    Postscript format

Main changes in version 2.1b compared to the previous NOST 100-2.0 version are:

Other related documents:


Version NOST 100-2.0 (March 1999):    PDF format,    Postscript format

Latex source files: fits_standard20.tex, nost.sty, ieee1.eps, ieee2.eps, fits_standard20.ind

This version of the Standard was published in the Astronomy & Astrophysics scientific journal in September 2001. This published version was endorsed by the IAU FITS Working Group in October 2000 and is identical to the original NOST document except for the addition of 2 introductory sections on the history of FITS and on the process that lead to the creation of the NOST document. There were also 2 minor clarifications on a) the interpretation of the word "deprecated" and b) the usage of the TDIMn keyword with variable length array columns.


Version NOST 100-1.2 (April 1998):    PDF format,    Postscript format

This version adds the Image and Binary Table standard extensions. List of changes between v1.1 and v1.2.

Latex source files: fits_standard.tex, nost.sty, ieee1.eps, ieee2.eps, fits_standard.ind


Version NOST 100-1.1 (September 29 1995):    Postscript format,    latex source


Version NOST 100-1.0 (June 1993):    PDF format,    Postscript format,    NOST announcement



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