**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 , 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
per hour in direction
and 4 metres per socond in distance. (RMS figures with respect
to JPL DE200 for the interval 1960-2025 are and
per hour in longitude, and

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.

Starlink User Note 67

P. T. Wallace

12 October 1999

E-mail:ptw@star.rl.ac.uk