baryvel {astrolibR} | R Documentation |
Calculates heliocentric and barycentric velocity components of Earth
baryvel(dje,deq)
dje |
Julian ephemeris date (scalar) |
deq |
epoch of mean equinox of dvelh and dvelb (scalar). If deq=0, then deq is assumed to be equal to dje. |
The 3-vectors DVELH and DVELB are given in a right-handed coordinate system with the +X axis toward the Vernal Equinox, and +Z axis toward the celestial pole.
The projected velocity towards the celestial object can be computed from: v = dvelb[1]*cos(dec)*cos(ra) + dvelb[2]*cos(dec)*sin(ra) + dvelb[3]*sin(dec)
The algorithm here is taken from FORTRAN program of Stumpff (1980). Stumpf claimed an accuracy of 42 cm/s for the velocity. A comparison with the JPL FORTRAN planetary ephemeris program PLEPH found agreement to within about 65 cm/s between 1986 and 1994. The option in IDL astrolib's baryvel.pro to use the full JPL ephemeris is not implemented in R.
dvelh |
heliocentric velocity components (3 element vector) in km/s |
dvelb |
barycentric velocity components (3 element vector) in km/s |
Jeff Valenti, U.C. Berkeley Translated BARVEL.FOR to IDL
R adaptation by Arnab Chakraborty June 2013
Two Self-Consistent FORTRAN Subroutines for the Computation of the Earth's Motion, P. Stumpff, Astronomy & Astrophysics Supplement, 41, 1, 1980.
baryvel(2456469.5, 0)