SLA_MAPPA - Mean to Apparent Parameters   

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 epoch of mean equinox to be used (Julian)

DATE D TDB (JD-2400000.5)

RETURNED:

AMPRMS 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)

$$\times 2 /$$ (8)

(9-11) v: barycentric Earth velocity in units of c

$$\sqrt{1-\left\vert\mbox{\bf v}\right\vert^2}$$ (12)

$$3\times3$$ (13-21)

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.