planets(1)						      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)