helio_jd {astrolibR} R Documentation

## 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)

### 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).

### Value

 `jdhelio` heliocentric reduced Julian date (but see time_diff)

### Author(s)

Written by W. Landsman STX 1989

R adaptation by Arnab Chakraborty June 2013

### References

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

`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))
```

[Package astrolibR version 0.1 Index]