The astronomy community uses, for archival and interchange of
image and tabular data,
a data storage convention known as FITS. The header of a FITS file
consists of a number of keyword/value pairs, embedded in a fixed
record format.
The FITS standard [FITS]
was inspired by Hollerith card images and is somewhat restrictive.
Keywords are limited to eight uppercase ASCII characters, and records are
strictly constructed by column position. Here is a brief sample from a
typical FITS image header.
SIMPLE = T / FITS type
BITPIX = 16 / bits/pixel
NAXIS = 2 / image axes
NAXIS1 = 2303 / dim in x
NAXIS2 = 1024 / dim in y
TEMPDET = -119.72433472 /
DEWARID = 29 /
TEMPSET = -119.95216370 /
DWRN2LV = 80.87911987 /
RESN2LV = 32.34042740 /
PWRBLOK = 3.17460322 /
UTBTEMP = 6.50000000 /
UTBTMPS = 5.00000000 /
UTBFANS = F /
AUTOSHUT= T /
A few mandatory FITS keywords specify the structure of the subsequent image or table data. Other, ``reserved" keywords document common characteristics of data (like DATE, TELESCOPE); the rest of the keyword namespace is commonly used to supply institution-specific, application-specific, or instrument-specific information.