premat {astrolibR}R Documentation

Return the precession matrix needed to go from EQUINOX1 to EQUINOX2

Description

Return the precession matrix needed to go from EQUINOX1 to EQUINOX2

Usage

premat(equinox1, equinox2, fk4=F)

Arguments

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)

Details

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.

Value

matrix

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

Author(s)

Written, Wayne Landsman, HSTX Corporation, 1994

R adaptation by Arnab Chakraborty June 2013

References

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

See Also

baryvel precess

Examples

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

premat(1950.0, 1975.0, fk4=TRUE)

[Package astrolibR version 0.1 Index]