SLA_MOON

Approx Moon Pos/Vel

ACTION:
Approximate geocentric position and velocity of the Moon (single precision).
CALL:
CALL sla_MOON (IY, ID, FD, PV)
GIVEN:
 IY I year ID I day in year (1 = Jan 1st) FD R fraction of day

RETURNED:
 PV R(6) Moon $\left[\phantom{\rule{0.3em}{0ex}}x,y,z,ẋ,ẏ,ż\phantom{\rule{0.3em}{0ex}}\right]$, mean equator and equinox of date (AU, AU s${}^{-1}$)

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 sla_CALYD or sla_CLYD.
(2)
The position is accurate to better than 0.5 arcminute in direction and 1000 km in distance. The velocity is accurate to better than ′′05 per hour in direction and 4 metres per second in distance. (RMS figures with respect to JPL DE200 for the interval 1960-2025 are $14\phantom{\rule{-0.54753pt}{0ex}}$${}^{\prime }{\phantom{\rule{-1.09506pt}{0ex}}}^{\prime }$ and ′′02 per hour in longitude, $9\phantom{\rule{-0.54753pt}{0ex}}$${}^{\prime }{\phantom{\rule{-1.09506pt}{0ex}}}^{\prime }$ and ′′02 per hour in latitude, 350 km and 2 metres per second in distance.) Note that the distance accuracy is comparatively poor because this routine is principally intended for computing topocentric direction.
(3)
This routine is only a partial implementation of the original Meeus algorithm (reference below), which offers 4 times the accuracy in direction and 20 times the accuracy in distance when fully implemented (as it is in sla_DMOON).
REFERENCE:
Meeus, l’Astronomie, June 1984, p348.