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"Dance of the planets" (last version 2.71)
was a DOS-program that calculated the instantaneous positions and velocities of the orbiting bodies.
The incremental movement of each body due to the gravitational influence of all others is continuously calculated, closely approximating the action of gravity. The result is an accurate dynamic model.
It even simulated the Shoemaker-Levy-9 collisions on Jupiter !
With this program it is so interesting to delete or add bodies to see what happen.
DotP "show" you the answer to questions like:
- What would happened to this comet, had Jupiter not been there ?
- Which orbit did this comet have before it encountered Jupiter.
An example of orbital sleuthing: periodic comet Oterma was discovered in 1942, seen for two more apparitions (1950 and 1958), and has since been lost. Starting the simulation in 1958, you can discover what happened.
Passing close to Jupiter in 1963, Oterma is thrown out into a more distant orbit - you can see where it is now.
But that is not all. Run the simulation back in time to find that in 1939 Jupiter pulled the comet in from a more distant orbit, changing its period from 21 to 8 years!
It then came close enough to the Sun and Earth to permit its 1942 discovery.

Peter van Grijfland.

(c) ARC Science Simulations (Photo)