node-ephem

node-ephem

Parse JPL DE planetary ephemerides and calculate the position of planets (and moon) at a given time.

This module is based on Project Pluto's code for calculating planetary positions from JPL ephemerides.

Required

This module uses publicly available planetery ephemeride files which can be downloaded from NASA's Jet Propulsion Laboratory FTP server. More information on which file to chose can be found here.

Usage

Require the module.

var ephem = require('node-ephem');

Load ephemerides which you downloaded, by providing a path to it:

var e430 = ephem.load('./eph/linux_p1550p2650.430');

Find Mars, relative to the Sun, at this instant:

var position = e430.find(ephem.bodies.MARS, ephem.bodies.SUN, ephem.julian(new Date));

Find RA/Dec of Neptune at this moment, adjusted for light-time:

var radec = ephem.equatorial(e430.observe(ephem.bodies.MERCURY, ephem.bodies.EARTH, ephem.julian(new Date)));

Functions

node-ephem exports:

Function	Parameters	Description
load	path	Load planetary ephemerides file, returns ephemeris object
julian	date	convert Date to Julian day (J2000 epoch, TT)
equatorial	position	Cartesian to Equаtorial

ephemeris object:

Function	Parameters	Description
find	body, observer, time	Find the position of body looking from observer at time
observe	body, observer, time	Find position of body adjusted for light-time
status		Returns constants from loaded epehmeris file and status

Planets

node-ephem provides a convenient name to code mapping via exported constants

Planet	Code
ephem.bodies.MERCURY	1
ephem.bodies.VENUS	2
ephem.bodies.EARTH	3
ephem.bodies.MARS	4
ephem.bodies.JUPITER	5
ephem.bodies.SATURN	6
ephem.bodies.URANUS	7
ephem.bodies.NEPTUNE	8
ephem.bodies.PLUTO	9
ephem.bodies.MOON	10
ephem.bodies.SUN	11

Testrunner

A testrunner is included which executes the test files available for DE files. Download the testpo file and place in the same directory as the ephemeris file, then run:

node testrunner.js

Follow the instructions.