planets - Man Page

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

a: Add Planet
j: Place random orbital planet
r: Place random planet
u: Undo (undoes last planet insertion)
e: Reset to empty universe
g: Go Back (goes back to just after last planet insertion)
Mouse: Click on a planet to delete it

Physics

b: Toggle bounce (experimental)

Display control

Cursor keys: Panning
c, Space: Move display to center of mass
x: Initiate center of mass tracking
=: Zoom in
-: Zoom out
p: Toggle Pause
o: Change all colors randomly
t: Toggle Trace
d: Double Trace Length
h: Halve Trace Length
Mouse: Drag a box around a set of planets to follow the center of mass of those planets

Program control

H: Display help dialog
k: Display option dialog
Ctrl-Shift-k: 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.
l: Load Universe After pressing l, press any other character to load the universe with that name. Universes are stored in ~/.planets/ .
s: Save Universe After pressing s, press any other character to save the universe with that name. Universes are saved in ~/.planets/ .
q, Esc: 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.