planets(1)planets(1)NAMEplanets - 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 simula‐
tion 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 <mar‐
tin@piware.de> for the Debian GNU/Linux system (but may be used by oth‐
ers).
April 20, 2003 planets(1)
