baryvel: Calculates heliocentric and barycentric velocity components...

In astrolibR: Astronomy Users Library

Description

Calculates heliocentric and barycentric velocity components of Earth

Usage

baryvel(dje,deq)

Arguments

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.

Details

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.

Value

dvelh	heliocentric velocity components (3 element vector) in km/s
dvelb	barycentric velocity components (3 element vector) in km/s

Author(s)

Jeff Valenti, U.C. Berkeley Translated BARVEL.FOR to IDL
R adaptation by Arnab Chakraborty June 2013

References

Two Self-Consistent FORTRAN Subroutines for the Computation of the Earth's Motion, P. Stumpff, Astronomy & Astrophysics Supplement, 41, 1, 1980.

Examples

baryvel(2456469.5, 0)

Example output

$dvelh
[1] 29.2000192  2.0667007  0.8957724

$dvelb
[1] 29.2108295  2.0674841  0.8958489

astrolibR documentation built on May 2, 2019, 3:26 a.m.