Comments on: Where can I find data on planetary positions and velocities?

Question: Where can I find data on planetary positions and velocities?

deansfurniture5 — Mon, 17 Mar 2008 13:33:41 -0800

I'm working on a computer simulation of the solar system, but I need data on the positions and velocities on planets and their moons. (more inside)

For a class project, I'm working on a 3D simulation of the solar system. However, I need to get good data on the positions and velocities of planets and their moons. I've managed to find a lot of sites with information about planetary positions as viewed from earth, but the way I'm constructing it, I need to be able to locate them by x, y, and z coordinates with the Sun at the origin.

Any ideas where I might find any good data? Also, anywhere with an analytical solution to the position of a planet with respect to the Sun would be helpful as well.

Thanks!

By: Guy_Inamonkeysuit

Guy_Inamonkeysuit — Mon, 17 Mar 2008 13:40:36 -0800

Here?

By: Upton O'Good

Upton O'Good — Mon, 17 Mar 2008 14:12:34 -0800

You might also check JPL's ephemeris[?] generator, available here (or more generally here)--this is the most detailed data, the sort used to make trajectories for interplanetary spacecraft, and accounts for gravitational interactions between the smaller bodies. They offer a number of types of data through the main SSD page as well--they can give you orbital elements if you just want to do a simple Keplerian model.

By: mumkin

mumkin — Mon, 17 Mar 2008 14:15:33 -0800

Stellarium is open source. Would it be cheating to use its data? Come to think of it, it may assume an earth-centric coordinate system. Howzabout Celestia?

By: njgo

njgo — Mon, 17 Mar 2008 15:49:44 -0800

If you have vectors for the sun and for the planets relative to earth, just subtract the position and velocity vector for the sun from the vectors for each planet to move to the sun's frame.

There is no analytical solution to the problem of n bodies interacting gravitationally... (not to mention effects from general relativity, solar wind interacting with planetary magnetospheres, asteroid belts and other nastiness). If you neglect everything besides gravitational interaction with the sun you get Keplerian orbits-check you favorite classical mechanics text for solutions.

By: deansfurniture5

deansfurniture5 — Mon, 17 Mar 2008 16:23:20 -0800

Thanks everyone for your help, I'll definitely be checking out the sites you suggested.

@njgo: I was looking for some way to predict the position of a planet x amount of time in the future so I can see how good my simulation is. I'm sure the basic orbits will be fine, which I found info on between posting the question and checking back. Thanks!