SUNPOS

       To compute the RA and Dec of the Sun at a given date.

       SUNPOS, jd, ra, dec, [elong, obliquity, /RADIAN ]

       jd    - The Julian date of the day (and time), scalar or vector
               usually double precision

       ra    - The right ascension of the sun at that date in DEGREES
               double precision, same number of elements as jd
       dec   - The declination of the sun at that date in DEGREES

       elong - Ecliptic longitude of the sun at that date in DEGREES.
       obliquity - the obliquity of the ecliptic, in DEGREES

       /RADIAN - If this keyword is set and non-zero, then all output variables
               are given in Radians rather than Degrees

       The accuracy in the 20th century  should be within 1"; however this
       has not been extensively tested.
       The returned RA and Dec are in the given date's equinox.
       Procedure was extensively revised in May 1996, and the new calling
       sequence is incompatible with the old one.

       Uses a truncated version of Newcomb's Sun.    Adapted from the IDL
       routine SUN_POS by CD Pike, which was adapted from a FORTRAN routine
       by B. Emerson (RGO).

       (1) Find the apparent RA and Dec of the Sun on May 1, 1982
       IDL> jdcnv, 1982, 5, 1,0 ,jd      ;Find Julian date jd = 2445090.5
       IDL> sunpos, jd, ra, dec
       IDL> print,adstring(ra,dec,2)
                02 31 32.61  +14 54 34.9
       The Astronomical Almanac gives 02 31 32.58 +14 54 34.9 so the error
               in SUNPOS for this case is < 0.5".
       (2) Find the apparent RA and Dec of the Sun for every day in 1997
       IDL> jdcnv, 1997,1,1,0, jd                ;Julian date on Jan 1, 1997
       IDL> sunpos, jd+ dindgen(365), ra, dec    ;RA and Dec for each day

       Written by Michael R. Greason, STX, 28 October 1988.
       Accept vector arguments, W. Landsman     April,1989
       Eliminated negative right ascensions.  MRG, Hughes STX, 6 May 1992.
       Rewritten using the 1993 Almanac.  Keywords added.  MRG, HSTX,
               10 February 1994.
       Major rewrite, improved accuracy, always return values in degrees
       W. Landsman  May, 1996
       Added /RADIAN keyword,    W. Landsman       August, 1997
       Converted to IDL V5.0   W. Landsman   September 1997

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