DragonFly On-Line Manual Pages

planets(1)             DragonFly General Commands Manual            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 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)