Orrery --- Planetary Motion

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Units: distance is in au (astronomical units), time is in years, and mass is in Earth masses. All calculations are done in these units. Time is discretized into 0.01 year increments.

In the display, radii are scaled to make the planets more than just tiny dots. This scaling is for display purposes only.

"dt" is the time increment in years (so 0.003 is approximately one day). Give a negative value for dt to run the simulation backwards.

The most time consuming part of the simulation is painting the window. Parameter "warp" indicates how many simulation time steps are performed per repainting. Large warp factors make the simulation run very fast.

"Rot. rate" counterrotates the frame of reference at the given rate. Setting it to 6.167 approximately freezes the motion of Earth. Inner planets continue in a forward direction whereas outer planets have a backwards apparent motion. Other values can be chosen to freeze the other planets. Use in conjuntion with a high warp value (say 500) and "Show Trails" to discover interesting resonances.

Move the mouse over the buttons for a more detailed explanation of their purpose.

L4 is the fourth Lagrange point of Earth. This is the point 1 au from the Sun but lagging the Earth by 2 months in its orbit. It is known that, in an Earth-Sun system, a satellite placed in orbit here will stay in this position indefinitely. It is not known whether the other planets destabilize this location or not. Run the simulation and see.

Can you find Pluto? It comes in and out of view at the corners of the window.