FITS

FITS
Name	FITS
Extension	.fit, .fits, .fts
Type	Digital file format
Owner	NASA / International Astronomical Union
Introduced	1981
Latest release	3.0 (2016)

FITS

The Flexible Image Transport System is a digital file format designed for the storage, interchange, and archival of scientific data, particularly in observational astronomy. It was created to support interoperability among missions and facilities such as NASA observatories, ground-based telescopes like Keck Observatory, space missions like Hubble Space Telescope, and facilities managed by organizations including the European Space Agency and the National Radio Astronomy Observatory. The format emphasizes self-describing metadata, long-term preservation, and compatibility with analysis systems used at institutions such as Harvard-Smithsonian Center for Astrophysics, Smithsonian Institution, and the Space Telescope Science Institute.

Overview

FITS is organized as a sequence of Header and Data Units (HDUs) that allow images, tables, and multidimensional arrays to be stored together with descriptive metadata. The design supports use across platforms used by projects like Sloan Digital Sky Survey, Chandra X-ray Observatory, Spitzer Space Telescope, ALMA, and the Very Large Array. Prominent data archives such as the Mikulski Archive for Space Telescopes, the European Southern Observatory archive, and the NASA/IPAC Infrared Science Archive rely on FITS for distribution. The format specification and governance involve stakeholders from the International Astronomical Union and national agencies such as NOIRLab.

History

Work on the format began in the late 1970s to unify disparate binary image formats used by facilities including Palomar Observatory and missions like International Ultraviolet Explorer. The original specification, endorsed in 1981, was developed by engineers and scientists from NASA, the European Space Agency, and observatory centers such as Cerro Tololo Inter-American Observatory. Subsequent revisions addressed table extensions introduced by projects including the Arecibo Observatory and the Anglo-Australian Telescope, and standardized conventions used by consortia such as the Two Micron All-Sky Survey team. Major milestones include the adoption of Binary Table extensions influenced by pipeline systems at Jet Propulsion Laboratory and formalization of World Coordinate System conventions driven by work at Caltech and International Astronomical Union working groups.

File format and structure

A FITS file comprises one or more HDUs; each HDU contains an ASCII header of 80-character keyword records followed by optional binary data blocks aligned to 2880-byte records. Headers use standardized keywords and conventions developed in coordination with institutions such as European Space Agency, Space Telescope Science Institute, and projects like Gaia to record provenance, instrument parameters, and coordinate frames. Data payloads can represent images (2D arrays), spectra, or tables; binary table extensions accommodate heterogeneous columns used by data releases from Sloan Digital Sky Survey and catalogs like Gaia Archive. The format supports ubiquitous keywords such as SIMPLE, BITPIX, NAXIS, and EXTNAME—each reflecting agreements made among data producers at centers including NOIRLab and archives such as the Mikulski Archive for Space Telescopes.

Usage in astronomy and other fields

FITS is the de facto standard for archival and interchange of astronomical images and associated metadata from observatories including Mauna Kea Observatories, European Southern Observatory, and missions like James Webb Space Telescope. Large surveys and missions—Sloan Digital Sky Survey, Gaia, Pan-STARRS, and Wide-field Infrared Survey Explorer—distribute calibrated images, catalogs, and spectra in FITS. Beyond astronomy, FITS has been used in fields connected to observatories and agencies such as Smithsonian Institution and NASA for planetary science from missions like Voyager and Cassini–Huygens, in solar physics with data from Solar and Heliospheric Observatory, and in radio astronomy at facilities including Atacama Large Millimeter Array. FITS’s self-describing headers make it attractive for archival uses at institutions like National Archives and Records Administration and for multidisciplinary projects involving geospatial and imaging datasets managed by agencies such as US Geological Survey.

Software and tools

A broad ecosystem of software reads and writes FITS, including libraries and applications developed at centers such as Space Telescope Science Institute and universities like Harvard University and UC Berkeley. Prominent libraries and tools include cfitsio (widely used in pipelines at Jet Propulsion Laboratory), FITSIO, Astropy utilities driven by contributors from Open Astronomy, and desktop viewers such as SAOImage DS9 originating at Smithsonian Astrophysical Observatory. Data reduction packages for instruments at Keck Observatory, European Southern Observatory, and missions like Chandra X-ray Observatory integrate FITS support. Virtual Observatory frameworks promoted by the International Virtual Observatory Alliance rely on FITS for data interchange, and pipelines at centers such as NOIRLab and European Space Agency implement FITS-based workflows.

Compatibility and extensions

FITS maintains backward compatibility across major revisions to ensure decades-old archives from facilities like Palomar Observatory and missions such as International Ultraviolet Explorer remain readable. Extensions and conventions—such as the Binary Table extension, tiled image compression schemes adopted by projects like ESA archives, and World Coordinate System conventions—are developed collaboratively by working groups including the International Astronomical Union FITS Working Group and contributors from NASA centers. Community-driven conventions address needs for large datasets in surveys like Sloan Digital Sky Survey and LSST (Vera C. Rubin Observatory), while translation layers and libraries enable interoperability with other formats used at institutions like CERN and in standards propagated by bodies such as ISO.

Category:Astronomical imaging formats