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).

                                                 April 20, 2003                                       planets(1)