**ACTION:**- Compute star-independent parameters in preparation for
conversions between mean place and geocentric apparent place.
The parameters produced by this routine are required in the
parallax, light deflection, aberration, and precession/nutation
parts of the mean/apparent transformations.
The reference frames and timescales used are post IAU 1976.
**CALL:**`CALL sla_MAPPA (EQ, DATE, AMPRMS)`

**GIVEN:**-

*EQ***D**epoch of mean equinox to be used (Julian) *DATE***D**TDB (JD-2400000.5)

**RETURNED:**-

*AMPRMS***D(21)**star-independent mean-to-apparent parameters: (1) time interval for proper motion (Julian years) (2-4) barycentric position of the Earth (AU) (5-7) heliocentric direction of the Earth (unit vector) (8) (gravitational radius of Sun)(Sun-Earth distance) (9-11) **v**: barycentric Earth velocity in units of c(12) (13-21) precession/nutation matrix

**NOTES:**- 1.
- For DATE, the distinction between the required TDB and TT is always negligible. Moreover, for all but the most critical applications UTC is adequate.
- 2.
- The accuracy of the routines using the parameters AMPRMS is limited by the routine sla_EVP, used here to compute the Earth position and velocity by the methods of Stumpff. The maximum error in the resulting aberration corrections is about 0.3 milliarcsecond.
- 3.
- The vectors AMPRMS(2-4) and AMPRMS(5-7) are referred to the mean equinox and equator of epoch EQ.
- 4.
- The parameters produced by this routine are used by sla_MAPQK and sla_MAPQKZ.

**REFERENCES:**- 1.
- 1984
*Astronomical Almanac*, pp B39-B41. - 2.
- Lederle & Schwan, 1984.
*Astr.Astrophys.***134**, 1-6.

Starlink User Note 67

P. T. Wallace

12 October 1999

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