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 time scales used are post IAU 1976.
CALL:: CALL sla_MAPPA (EQ, DATE, AMPRMS)

EQ	D	epoch of mean equinox to be used (Julian)

DATE	D	TDB (JD $-$ 2400000.5)

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) $\times 2 /$ (Sun-Earth distance)
(9-11)		v: barycentric Earth velocity in units of c
(12)		$\sqrt{1 - {\|v\|}^{2}}$
(13-21)		precession-nutation $3 \times 3$ 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 vectors AMPRMS(2-4) and AMPRMS(5-7) are (in essence) referred to the mean equinox and equator of epoch EQ. For EQ=2000D0, they are referred to the ICRS.
(3): The parameters produced by this routine are used by sla_MAPQK, sla_MAPQKZ and sla_AMPQK.
(4): The accuracy, starting from ICRS star data, is limited to about 1 mas by the precession-nutation model used, SF2001. A different precession-nutation model can be introduced by first calling the present routine and then replacing the precession-nutation matrix in AMPRMS(13-21) directly.
(5): A further limit to the accuracy of routines using the parameter array AMPRMS is imposed 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.

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