premat: Return the precession matrix needed to go from EQUINOX1 to...
In astrolibR: Astronomy Users Library

Description Usage Arguments Details Value Author(s) References See Also Examples

Return the precession matrix needed to go from EQUINOX1 to EQUINOX2

1	premat(equinox1, equinox2, fk4=F)

`equinox1`	original equinox of coordinates, scalar
`equinox2`	equinox of precessed coordinates
`fk4`	if =TRUE, the FK4 (B1950.0) system will be used; otherwise FK5 (J2000.0) will be used (default = FALSE)

This matrix is used by the functions precess and baryvel to precess astronomical coordinates. The algorithm of this function is obtained from Taff (1983, p.24) for FK4. FK5 constants are obtained from "Astronomical Almanac Explanatory Supplement (1992), page 104, Table 3.211.1.

matrix

3 x 3 precession matrix, used to precess equatorial rectangular coordinates

Written, Wayne Landsman, HSTX Corporation, 1994

R adaptation by Arnab Chakraborty June 2013

Taff, L. G., 1983, "Computational Spherical Astronomy", Krieger Publ.

baryvel precess

1
2
3

#  Return the precession matrix from 1950.0 to 1975.0 in the FK4 system

premat(1950.0, 1975.0, fk4=TRUE)

            [,1]          [,2]          [,3]
[1,] 0.999981438 -5.587750e-03 -2.429085e-03
[2,] 0.005587750  9.999844e-01 -6.786915e-06
[3,] 0.002429085 -6.786331e-06  9.999970e-01