.help dmoon Jun99 "Slalib Package"
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      SUBROUTINE slDMON (DATE, PV)

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      D M O N
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  Approximate geocentric position and velocity of the Moon
  (double precision)

  Given:
     DATE       D       TDB (loosely ET) as a Modified Julian Date
                                                    (JD-2400000.5)

  Returned:
     PV         D(6)    Moon x,y,z,xdot,ydot,zdot, mean equator and
                                         equinox of date (AU, AU/s)

  Notes:

  1  This routine is a full implementation of the algorithm
     published by Meeus (see reference).

  2  Meeus quotes accuracies of 10 arcsec in longitude, 3 arcsec in
     latitude and 0.2 arcsec in HP (equivalent to about 20 km in
     distance).  Comparison with JPL DE200 over the interval
     1960-2025 gives RMS errors of 3.7 arcsec and 83 mas/hour in
     longitude, 2.3 arcsec and 48 mas/hour in latitude, 11 km
     and 81 mm/s in distance.  The maximum errors over the same
     interval are 18 arcsec and 0.50 arcsec/hour in longitude,
     11 arcsec and 0.24 arcsec/hour in latitude, 40 km and 0.29 m/s
     in distance. 

  3  The original algorithm is expressed in terms of the obsolete
     timescale Ephemeris Time.  Either TDB or TT can be used, but
     not UT without incurring significant errors (30 arcsec at
     the present time) due to the Moon's 0.5 arcsec/sec movement.

  4  The algorithm is based on pre IAU 1976 standards.  However,
     the result has been moved onto the new (FK5) equinox, an
     adjustment which is in any case much smaller than the
     intrinsic accuracy of the procedure.

  5  Velocity is obtained by a complete analytical differentiation
     of the Meeus model.

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

  P.T.Wallace   Starlink   22 January 1998

  Copyright (C) 1998 Rutherford Appleton Laboratory
  Copyright (C) 1995 Association of Universities for Research in Astronomy Inc.

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