Gravity Simulator
General >> Discussion >> Neptune Trojans

Message started by phoenixshade on 01/20/11 at 11:35:10

Title: Neptune Trojans
Post by phoenixshade on 01/20/11 at 11:35:10

Just trying out the screen output feature for the first time.

I know I've seen this simulation before, only without the L5 Neptune trojan (2008 LC18). This shows the evolution of their orbits over the next ~20k years (119 orbits). The orbital elements are taken from the IAU Minor Planet Center (
Sorry about the large image size; you can see the full-size image here (

(Question: How can I get the rotating frame to compensate for the variations in Neptune's period over the course of the simulation? I want to correct for that drift...)

Title: Re: Neptune Trojans
Post by Tony on 01/20/11 at 21:29:11

Nice animation!

Neptune drifts because Gravity Simulator computes its period as if it's the only object orbiting the sun.  With the rest of the planets present, it is perturbed from this period.

To correct the drift, open the "Rotating Frame Adjustment" interface from the "View" menu.  Press the "Calibrate" button.  The mouse pointer turns into cross-hairs.  Click on Neptune.  Wait a few minutes for Neptune to drift a bit, then click on it again.  The mouse pointer now returns back to normal.  This pair of clicks tells Gravity Simulator how fast Neptune is drifting, and it adjusts accordingly.

You can also manually enter the rotating period in seconds.  Try these values to minimize drift (or create your own list of values):
Mercury: 7594275.41860666
Venus: 19414152.0111384
Earth:   31558120.0235718
Mars: 59355038.3065867
Neptune: 5199835596.89369
moon: 2359985.26500568

You'll notice that at faster time steps, objects will drift again.  This is because of numerical error introduced by taking large time steps.  So you might want to experiment and create a list of times for various time steps so in the future you can manually paste them into the time step period box.

Gravity Simulator » Powered by YaBB 2.1!
YaBB © 2000-2005. All Rights Reserved.