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
- 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.
BUGS
Currently bouncing doesn't work very well unless you make the timeslice 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).