slaMoon -

SYNOPSYS

PARAMETERS

int iy

int id

double fd

float *posvel

DESCRIPTION

  Approximate geocentric position and velocity of the Moon.

Given

     iy       int        year AD
     id       int        day in year (1 = Jan 1st)
     fd       float      fraction of day

Returned

     posvel   float[6]   Moon position & velocity vector

Called

     slaCs2c6, slaEuler, slaMxv

  The date and time is TDB (loosely ET) in the Gregorian
  calendar, and is interpreted in a manner which is valid
  between 1900 March 1 and 2100 February 28.

  The Moon 6-vector is Moon centre relative to Earth centre,
  mean equator and equinox of date.  Position part, posvel(0-2),
  is in AU;  velocity part, posvel(3-5), is in AU/sec.

  The position is accurate to better than 0.5 arcminute
  in direction and 1e-5 AU in distance.  The velocity
  is accurate to better than 0.5"/hour in direction and
  4 m/s in distance.  Note that the distance accuracy is
  comparatively poor because this routine is merely
  intended for use in computing topocentric direction.

Reference

     Meeus, l'Astronomie, June 1984, p348.

  This routine is only a partial implementation of the original
  algorithm, which offers somewhat higher accuracy in direction
  and much higher accuracy in distance (or rather in horizontal
  parallax) when fully implemented.

  P.T.Wallace   Starlink   16 November 1993

SEE ALSO

• slalib.3