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Model of a solar nebula that shows the accretion of a star by gravitational forces from an initial cloud of particles with random vectors. This has been adapted so that

  1. trails for all the stars can be turned on and off,
  2. you can select a specific star to show its trail by clicking on it,
  3. you can tag a ride on a star by clicking on it,
  4. you can pause and restart the simulation ("s" and "g" keys).


Download software

Operating System Download
All OSs (with VPython installed) or (right click to download)
Windows XP and Vista installer nebula_20p_GeoMod.exe (2.9 Mb)

Multimedia Demonstrations


This is a model of the gravitational collapse of a number of particles in space. Particles start with semi-randomly assigned initial positions and masses and their motion is governed by their initial velocity and Newtonian attraction. When particles collide they coalesce and eventually, a central star forms while a few planets remain in orbit. Because the final orbits do not lie on a single plane this model can be used to explain both the advantages and limitations of numerical modeling. This model was originally created by Chabay and Sherwood (2007a) but has been adapted so that selected planets leave trails that mark their orbits and so that the point of view (camera) can follow the motion of the planets. The tracing of orbits demonstrates orbital variability and the interaction of the planets. The ability to follow a planet's point of view was put in to incite student interest, and magnifies the changes in planetary velocity in different parts of the orbit.


  • The model has been used as part of an introductory class on Earth Sciences for the
    • lecture on the formation of the solar system, and
    • lab on the formation of the Earth.

User's Guide: Model Controls


  • General
    • If you click on a star it's trail will begin to show its trail. (If the star already has a trail the trail will turn off).
  • Buttons
    • Trails - switches on or off the trails for all stars except those tagged by clicking on them as described above.
    • Ride - lets the view of the scene follow the next star you click on.
      • When you click on a star with the Ride button set to On it will show the trail of the star as well as the view from the star itself.
  • Keys
    • Press "s" to pause the simulation (you can still zoom and rotate the scene).
    • Press "g" to restart.


  • When you Ride on a star, the center of the view always faces the center of the co-ordinate system (0,0,0). This makes for very interesting changes in perspective because the central star tends not to be at the origin.
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