Description:
Convert star RA,Dec from geocentric apparent to mean place. The " mean" coordinate system
is in fact close to ICRS. Use of this function is appropriate when efficiency is important
and where many star positions are all to be transformed for one epoch and equinox.
The star-independent parameters can be obtained by calling the palMappa function.
Invocation
void palAmpqk ( double ra, double da, double amprms[21], double
rm, double
dm
)
Arguments
ra = double (Given)
Apparent RA (radians).
da = double (Given)
Apparent Dec (radians).
amprms = double[21] (Given)
Star-independent mean-to-apparent
parameters (see palMappa): (0) time interval for proper motion (Julian years) (1-3) barycentric
position of the Earth (AU) (4-6) heliocentric direction of the Earth (unit vector) (7) (grav rad
Sun)2/(Sun-Earth
distance) (8-10) abv: barycentric Earth velocity in units of c (11)
sqrt(1-vv)
where v=modulus(abv) (12-20) precession/nutation (3,3) matrix
rm = double (Returned)
Mean RA
(radians).
dm = double (Returned)
Mean Dec (radians).
Note
Iterative techniques are used for
the aberration and light deflection corrections so that the routines palAmp (or palAmpqk) and
palMap (or palMapqk) are accurate inverses; even at the edge of the Sun’ s disc the discrepancy is
only about 1 nanoarcsecond.
Copyright © 2012 Science and Technology Facilities Council.
Copyright © 2014 Cornell University.
Copyright © 2015 Tim Jenness