precess - Precess the ra and dec columns from one equinox to another.

SYNOPSYS

        preces sys eq0 eq1 < file

Precess the ra and dec columns of an starbase data table from an equinox in either FK4 (Bessel-Newcomb, pre-IAU1976) or the FK5 (Fricke, post-IAU1976) system as indicated with the sys parameter.

OPTIONS

• -i file Read input from file instead of the standard input.
• -o file Write output to file instead of the standard output.

• sys

  The coordinate system for precession. One of "FK4|fk4|FK5|fk5".

• eq0

  The initial equinox.

• eq1

  The final equinox.

• rcol

  The column name of the ra column defaults to "ra". The column should contain RA coordinate values in hours.

• dcol

  The column name of the dec column defaults to "dec". The column should contain Dec coordinate values in degrees.

The epochs are Besselian if sys='FK4' and Julian if 'FK5'. For example, to precess coordinates in the old system from equinox 1900.0 to 1950.0 the command would be

         precess FK4 1900.0 1950.0 < targets

This routine will not correctly convert between the old and the new systems - for example conversion from B1950 to J2000. For these purposes see fk45z and fk54z .

SEE ALSO

• fk45z - convert ra, dec columns from fk4 to fk5 assuming zero proper motion.
• fk54z - convert ra, dec columns from fk5 to fk4 assuming zero proper motion.
• fk425 - convert ra, dec columns from fk4 to fk5 with proper motion, paralax and recession velocity.
• fk524 - convert ra, dec columns from fk5 to fk4 with proper motion, paralax and recession velocity.

• starbase.1 starbase data table introduction.
• starbase.3 starbase data table C library.
• starbase.5 starbase data table file format.