helio: Compute (low-precision) heliocentric coordinates for the...

In astrolibR: Astronomy Users Library

Description

Compute (low-precision) heliocentric coordinates for the planets

Usage

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

See Also

cirrange

Examples

# (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

$hrad
         [,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.