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.

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.

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)));

node-ephem exports:

ephemeris object:

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

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.