# helio: Compute (low-precision) heliocentric coordinates for the... In astrolibR: Astronomy Users Library

## Description

Compute (low-precision) heliocentric coordinates for the planets

## Usage

 `1` ```helio(jd, list1, radian=FALSE) ```

## Arguments

 `jd` Julian date, scalar or vector `list1` List of planets array. May be a single number. 1 = merc, 2 = venus, ... 9 = pluto `radian` If =TRUE, then the output longitude and latitude are given in radians. If =FALSE, the output are in degrees. (default=FALSE)

## Details

The mean orbital elements for epoch J2000 are used. These are derived from a 250 yr least squares fit of the DE 200 planetary ephemeris to a Keplerian orbit where each element is allowed to vary linearly with time. For dates between 1800 and 2050, this solution fits the terrestrial planet orbits to ~25" or better, but achieves only ~600" precision for Saturn.

These output arrays are dimensioned Nplanet x Ndate, where Nplanet is the number of elements of list1, and Ndate is the number of elements of Jjd.

Use planet_coords (which calls helio) to get celestial (RA, Dec) coordinates of the planets

## Value

 `hrad` array of heliocentric radii, in Astronomical Units `hlong` array of heliocentric (ecliptic) longitudes, in degrees or radians `hlat` array of heliocentric latitudes, in degrees or radians

## Author(s)

R. Sterner 1986 and W. Landsman 2000

R adaptation by Arnab Chakraborty June 2013

`cirrange`

## Examples

 ```1 2 3 4 5 6 7 8 9``` ```# (1) Find the current heliocentric positions of all the planets jd_today <- 2456877.5 helio(jd_today,seq(1,9)) # (2) Find heliocentric position of Mars on August 23, 2000 # Result: hrad = 1.6407 AU hlong = 124.3197 hlat = 1.7853 # For comparison, the JPL ephemeris gives hrad = 1.6407 AU hlong = 124.2985 hlat = 1.7845 helio(2451779.5,4) ```

### Example output

```\$hrad
[,1]
[1,]  0.3313886
[2,]  0.7199614
[3,]  1.0140554
[4,]  1.4780480
[5,]  5.2700807
[6,]  9.9208736
[7,] 20.0199531
[8,] 29.9746312
[9,] 32.7056263

\$hlong
[,1]
[1,] 132.21709
[2,]  84.77771
[3,] 315.19399
[4,] 259.63245
[5,] 122.79411
[6,] 232.52341
[7,]  13.64157
[8,] 335.85673
[9,] 281.90092

\$hlat
[,1]
[1,]  6.96410888
[2,]  0.48022343
[3,]  0.00100429
[4,] -0.92733046
[5,]  0.49285500
[6,]  2.17568235
[7,] -0.67010644
[8,] -0.72341031
[9,]  2.46805608

[,1]
[1,] 1.640733

\$hlong
[,1]
[1,] 124.3197

\$hlat
[,1]
[1,] 1.78532
```

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