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 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).