GET_EQUINOX

       Return the equinox value from a FITS header.

       Checks for 4 possibilities:
       (1)  If the EQUINOX keyword is found and has a numeric value, then this
               value is returned
       (2)  If the EQUINOX keyword has the values 'J2000' or 'B1950', then
               either 2000. or 1950. is returned.
       (3)  If the EQUINOX keyword is not found, then GET_EQUINOX will return
               the EPOCH keyword value.   This usage of EPOCH is disparaged.
       (4)  If neither EQUINOX no EPOCH is found, then the RADECSYS keyword
               is checked.   If the value is 'ICRS' or 'FK5' then 2000 is
               is returned, if it is 'FK4' then 1950 is returned.
       According Calabretta & Greisen (2002, A&A, 395, 1077) the EQUINOX should
       be written as a numeric value, as in format (1).   However, in older
       FITS headers, the EQUINOX might have been written using formats (2) or
       (3).

       Year = GET_EQUINOX( Hdr, [ Code ] )

       Hdr - FITS Header, string array, will be searched for the EQUINOX
               (or EPOCH) keyword.

       Year - Year of equinox in FITS header, numeric scalar

       Code - Result of header search, scalar
               -1 - EQUINOX, EPOCH or RADECSYS keyword not found in header
               0 - EQUINOX found as a numeric value
               1 - EPOCH keyword used for equinox (not recommended)
               2 - EQUINOX found as  'B1950'
               3 - EQUINOX found as  'J2000'
               4 - EQUINOX derived from value of RADECSYS keyword
                   'ICRS', 'FK5' ==> 2000,  'FK4' ==> 1950

       ZPARCHECK, SXPAR()

       Written  W. Landsman        STX              March, 1991
       Converted to IDL V5.0   W. Landsman   September 1997
       Don't use !ERR          W. Landsman   February 2000
       N = 1 for check of EPOCH keyword, not 0 S. Ott July 2000

[Home Page] [Software, Documentation] [IDL Documentation] [Quick Reference] [Feedback]