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HELIO_JD

HELIO_JD

Purpose

Convert geocentric (reduced) Julian date to heliocentric Julian date

Explanation

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/

Calling Sequence

jdhelio = HELIO_JD( date, ra, dec, /B1950, /TIME_DIFF)

Inputs

date - reduced Julian date (= JD - 2400000), scalar or vector, MUST
be double precision
ra,dec - scalars giving right ascension and declination in DEGREES
Equinox is J2000 unless the /B1950 keyword is set

Outputs

jdhelio - heliocentric reduced Julian date. If /TIME_DIFF is set, then
HELIO_JD() instead returns the time difference in seconds
between the geocentric and heliocentric Julian date.

Optional Input Keywords

/B1950 - if set, then input coordinates are assumed to be in equinox
B1950 coordinates.
/TIME_DIFF - if set, then HELIO_JD() returns the time difference
(heliocentric JD - geocentric JD ) in seconds

Example

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?
IDL> juldate, [1973,6,15,11,40], jd ;Get geocentric Julian date
IDL> hjd = helio_jd( jd, ten(20,9,7.8)*15., ten(37,9,7) )

==> hjd = 41848.9881
Wayne Warren (Raytheon ITSS) has compared the results of HELIO_JD with the
FORTRAN subroutines in the STARLINK SLALIB library (see
http://star-www.rl.ac.uk/).
Time Diff (sec)
1999-10-29T00:00:00.0 21 08 25. -67 22 00. -59.0 -59.0
1999-10-29T00:00:00.0 02 56 33.4 +00 26 55. 474.1 474.1
1940-12-11T06:55:00.0 07 34 41.9 -00 30 42. 366.3 370.2
1992-02-29T03:15:56.2 12 56 27.4 +42 10 17. 350.8 350.9
2000-03-01T10:26:31.8 14 28 36.7 -20 42 11. 243.7 243.7
2100-02-26T09:18:24.2 08 26 51.7 +85 47 28. 104.0 108.8

Procedures Called

bprecess, xyz, zparcheck

Revision History

Algorithm from the book Astronomical Photometry by Henden, p. 114
Written, W. Landsman STX June, 1989
Make J2000 default equinox, add B1950, /TIME_DIFF keywords, compute
variation of the obliquity W. Landsman November 1999

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