Name

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      GLACTC

Purpose

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        Convert between celestial and Galactic (or Supergalactic) coordinates.

Explanation

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      Program to convert right ascension (ra) and declination (dec) to
      Galactic longitude (gl) and latitude (gb) (j=1) or vice versa (j=2).

Calling Sequence

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      GLACTC, ra, dec, year, gl, gb, j, [ /DEGREE, /FK4, /SuperGalactic ]

Input Parameters

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      year equinox of ra and dec, scalar (input)
      j direction of conversion (input)
              1: ra,dec --> gl,gb
              2: gl,gb --> ra,dec
  INPUTS OR OUTPUT PARAMETERS: ( depending on argument J )
      ra Right ascension, hours (or degrees if /DEGREES is set),
                        scalar or vector
      dec Declination, degrees,scalar or vector
      gl Galactic longitude, degrees, scalar or vector
      gb Galactic latitude, degrees, scalar or vector
      All results forced double precision floating.

Optional Input Keyword Parameters

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      /DEGREE - If set, then the RA parameter (both input and output) is
                given in degrees rather than hours.
      /FK4 - If set, then the celestial (RA, Dec) coordinates are assumed
              to be input/output in the FK4 system. By default, coordinates
              are assumed to be in the FK5 system. For B1950 coordinates,
              set the /FK4 keyword *and* set the year to 1950.
      /SuperGalactic - If set, the GLACTC returns SuperGalactic coordinates
              as defined by deVaucouleurs et al. (1976) to account for the
              local supercluster. The North pole in SuperGalactic coordinates
              has Galactic coordinates l = 47.47, b = 6.32, and the origin is
              at Galactic coordinates l = 137.37, b= 0
             

Examples

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      Find the Galactic coordinates of Altair (RA (J2000): 19 50 47
      Dec (J2000): 08 52 06)
      IDL> glactc, ten(19,50,47),ten(8,52,6),2000,gl,gb,1
      ==> gl = 47.74, gb = -8.91

Procedure Calls

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      BPRECESS, JPRECESS, PRECESS

History

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      FORTRAN subroutine by T. A. Nagy, 21-MAR-78.
      Conversion to IDL, R. S. Hill, STX, 19-OCT-87.
      Modified to handle vector input, E. P. Smith, GSFC, 14-OCT-94
      Converted to IDL V5.0 W. Landsman September 1997
      Added DEGREE keyword, C. Markwardt, Nov 1999
      Major rewrite, default now FK5 coordinates, added /FK4 keyword
      use external precession routines W. Landsman April 2002
      Add /Supergalactic keyword W. Landsman September 2002
      Fix major bug when year not 2000 and /FK4 not set W. Landsman July 2003