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planets(1) General Commands Manual planets(1)

NAME

planets - Gravitational simulation of planetary bodies

DESCRIPTION

Planets is a simple interactive program for playing with simulations of planetary systems. It is great teaching tool for understanding how gravitation works on a planetary level.

The user interface is aimed at being simple enough for a fairly young kid can get some joy of it. There's also a special kid-mode aimed at very young children which grabs the focus and converts key banging into lots of random planets.

KEYBINDINGS

Universe definition

Add Planet
Place random orbital planet
Place random planet
Undo (undoes last planet insertion)
Reset to empty universe
Go Back (goes back to just after last planet insertion)
Click on a planet to delete it

Physics

Toggle bounce (experimental)

Display control

Panning
Move display to center of mass
Initiate center of mass tracking
=
Zoom in
-
Zoom out
Toggle Pause
Change all colors randomly
Toggle Trace
Double Trace Length
Halve Trace Length
Drag a box around a set of planets to follow the center of mass of those planets

Program control

Display help dialog
Display option dialog
Toggle kid-mode. Kid mode locks the keyboard and mouse, so the only way to get out is to toggle kid-mode again to get out.
Load Universe After pressing l, press any other character to load the universe with that name. Universes are stored in ~/.planets/ .
Save Universe After pressing s, press any other character to save the universe with that name. Universes are saved in ~/.planets/ .
Quit

TECHNICAL DETAILS

Planets uses a fourth-order runge-kutta approximation for the simulation itself. Planet bouncing is achieved by adding a repulsive force to planets at close quarters. Planets is fairly flexible: you can change the gravitational constant, the time-slice of the simulation, and even the exponent used in the gravitational law. Universes are saved in the ~/.planets directory, and are simple human readable and editable files.

BUGS

Currently bouncing doesn't work very well unless you make the time-slice quite small. Ideally, it would be nice to have a billiard-style bounce system, but it's not clear how to do this accurately in the presence of a strong gravitational field.

AUTHOR

Planets was written by Yaron M. Minsky <yminsky@cs.cornell.edu> as a gift for his nephew, Eyal Minsky-Fenick.

This manpage was contributed originally by Martin Pitt <martin@piware.de> for the Debian GNU/Linux system (but may be used by others).

April 20, 2003