MOONPOS

       To compute the RA and Dec of the Moon at specified Julian date(s).

       MOONPOS, jd, ra, dec, dis, geolong, geolat, [/RADIAN ]

       JD - Julian date, scalar or vector, double precision suggested

       Ra  - Apparent right ascension of the moon in DEGREES, referred to the
               true equator of the specified date(s)
       Dec - The declination of the moon in DEGREES
       Dis - The Earth-moon distance in kilometers (between the center of the
             Earth and the center of the Moon).
       Geolong - Apparent longitude of the moon in DEGREES, referred to the
               ecliptic of the specified date(s)
       Geolat - Apparent longitude of the moon in DEGREES, referred to the
               ecliptic of the specified date(s)
       The output variables will all have the same number of elements as the
       input Julian date vector, JD.   If JD is a scalar then the output
       variables will be also.

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

       (1) Find the position of the moon on April 12, 1992
       IDL> jdcnv,1992,4,12,0,jd    ;Get Julian date
       IDL> moonpos, jd, ra ,dec     ;Get RA and Dec of moon
       IDL> print,adstring(ra,dec,1)
               ==> 08 58 45.23  +13 46  6.1
       This is within 1" from the position given in the Astronomical Almanac
       (2) Plot the Earth-moon distance for every day at 0 TD in July, 1996
       IDL> jdcnv,1996,7,1,0,jd                   ;Get Julian date of July 1
       IDL> moonpos,jd+dindgen(31), ra, dec, dis  ;Position at all 31 days
       IDL> plot,indgen(31),dis, /YNOZ

       Derived from the Chapront ELP2000/82 Lunar Theory (Chapront-Touze' and
       Chapront, 1983, 124, 50), as described by Jean Meeus in Chapter 47 of
       ``Astronomical Algorithms'' (Willmann-Bell, Richmond), 2nd edition,
       1998.    Meeus quotes an approximate accuracy of 10" in longitude and
       4" in latitude, but he does not give the time range for this accuracy.
       Comparison of this IDL procedure with the example in ``Astronomical
       Algorithms'' reveals a very small discrepancy (~1 km) in the distance
       computation, but no difference in the position calculation.
       This procedure underwent a major rewrite in June 1996, and the new
       calling sequence is *incompatible with the old* (e.g. angles now
       returned in degrees instead of radians).

       CIRRANGE, ISARRAY(), NUTATE, TEN()  - from IDL Astronomy Library
       POLY() - from IDL User's Library

       Written by Michael R. Greason, STX, 31 October 1988.
       Major rewrite, new (incompatible) calling sequence, much improved
               accuracy,       W. Landsman   Hughes STX      June 1996
       Added /RADIAN keyword  W. Landsman August 1997
       Converted to IDL V5.0   W. Landsman   September 1997
       Use improved expressions for L',D,M,M', and F given in 2nd edition of
            Meeus (very slight change),  W. Landsman    November 2000
       Avoid 32767 overflow   W. Landsman January 2005

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