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.help prec Jun99 "Slalib Package"
.nf
SUBROUTINE slPREC (EP0, EP1, RMATP)
- - - - -
P R E C
- - - - -
Form the matrix of precession between two epochs (IAU 1976, FK5)
(double precision)
Given:
EP0 dp beginning epoch
EP1 dp ending epoch
Returned:
RMATP dp(3,3) precession matrix
Notes:
1) The epochs are TDB (loosely ET) Julian epochs.
2) The matrix is in the sense V(EP1) = RMATP * V(EP0)
3) Though the matrix method itself is rigorous, the precession
angles are expressed through canonical polynomials which are
valid only for a limited time span. There are also known
errors in the IAU precession rate. The absolute accuracy
of the present formulation is better than 0.1 arcsec from
1960AD to 2040AD, better than 1 arcsec from 1640AD to 2360AD,
and remains below 3 arcsec for the whole of the period
500BC to 3000AD. The errors exceed 10 arcsec outside the
range 1200BC to 3900AD, exceed 100 arcsec outside 4200BC to
5600AD and exceed 1000 arcsec outside 6800BC to 8200AD.
The SLALIB routine slPREL implements a more elaborate
model which is suitable for problems spanning several
thousand years.
References:
Lieske,J.H., 1979. Astron.Astrophys.,73,282.
equations (6) & (7), p283.
Kaplan,G.H., 1981. USNO circular no. 163, pA2.
Called: slDEUL
P.T.Wallace Starlink 23 August 1996
Copyright (C) 1996 Rutherford Appleton Laboratory
Copyright (C) 1995 Association of Universities for Research in Astronomy Inc.
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