.help moon Jun99 "Slalib Package"
.nf

      SUBROUTINE slMOON (IY, ID, FD, PV)

     - - - - -
      M O O N
     - - - - -

  Approximate geocentric position and velocity of the Moon
  (single precision).

  Given:
     IY       i       year
     ID       i       day in year (1 = Jan 1st)
     FD       r       fraction of day

  Returned:
     PV       r(6)    Moon position & velocity vector

  Notes:

  1  The date and time is TDB (loosely ET) in a Julian calendar
     which has been aligned to the ordinary Gregorian
     calendar for the interval 1900 March 1 to 2100 February 28.
     The year and day can be obtained by calling slCAYD or
     slCLYD.

  2  The Moon 6-vector is Moon centre relative to Earth centre,
     mean equator and equinox of date.  Position part, PV(1-3),
     is in AU;  velocity part, PV(4-6), is in AU/sec.

  3  The position is accurate to better than 0.5 arcminute
     in direction and 1000 km in distance.  The velocity
     is accurate to better than 0.5"/hour in direction and
     4 m/s in distance.  (RMS figures with respect to JPL DE200
     for the interval 1960-2025 are 14 arcsec and 0.2 arcsec/hour in
     longitude, 9 arcsec and 0.2 arcsec/hour in latitude, 350 km and
     2 m/s in distance.)  Note that the distance accuracy is
     comparatively poor because this routine is principally intended
     for computing topocentric direction.

  4  This routine is only a partial implementation of the original
     Meeus algorithm (reference below), which offers 4 times the
     accuracy in direction and 30 times the accuracy in distance
     when fully implemented (as it is in slDMON).

  Reference:
     Meeus, l'Astronomie, June 1984, p348.

  Called:  slS2C6

  P.T.Wallace   Starlink   8 December 1994

  Copyright (C) 1995 Rutherford Appleton Laboratory
  Copyright (C) 1995 Association of Universities for Research in Astronomy Inc.

.fi
.endhelp
