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)