astrolibR (version 0.1)

helio_jd: Convert geocentric (reduced) Julian date to heliocentric Julian date

Description

Convert geocentric (reduced) Julian date to heliocentric Julian date

Usage

helio_jd(date, ra, dec, B1950=FALSE, time_diff=FALSE)

Arguments

date

reduced Julian date (= JD - 2400000), scalar or vector

ra,dec

scalars giving right ascension and declination, in degrees

B1950

If =FALSE, equinox is J2000, if =TRUE, equinox is B1950 (default = FALSE)

time_diff

If =TRUE, then the function returns the time difference (heliocentric JD - geocentric JD), in seconds (default=FALSE)

Value

jdhelio

heliocentric reduced Julian date (but see time_diff)

Details

This procedure correct for the extra light travel time between the Earth and the Sun. An online calculator for this quantity is available at http://www.physics.sfasu.edu/astro/javascript/hjd.html. Users requiring more precise calculations and documentation should look at the IDL code available at http://astroutils.astronomy.ohio-state.edu/time/. The algorithm here is from Henden and Kaitchuck (1982, p.114).

References

Henden, A. A. and Kaitchuck, R. H., 1982, "Astronomical Photometry", Van Nostrand Reinhold

See Also

bprecess xyz

Examples

# What is the heliocentric Julian date of an observation of V402 Cygni
# (J2000: RA = 20 9 7.8, Dec = 37 09 07) taken June 15, 1973 at 11:40 UT?
# Result: hjd = 41848.9881

jd <- juldate(c(1973,6,15,11,40))   #  Get geocentric Julian date
hjd <- helio_jd(jd, ten(20,9,7.8)*15., ten(37,9,7))