1planets(1)                  General Commands Manual                 planets(1)
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NAME

6       planets - Gravitational simulation of planetary bodies
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DESCRIPTION

9       Planets is a simple interactive program for playing with simulations of
10       planetary systems. It is great  teaching  tool  for  understanding  how
11       gravitation works on a planetary level.
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13       The  user  interface is aimed at being simple enough for a fairly young
14       kid can get some joy of it.  There's also a special kid-mode  aimed  at
15       very young children which grabs the focus and converts key banging into
16       lots of random planets.
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KEYBINDINGS

19   Universe definition
20       a      Add Planet
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22       j      Place random orbital planet
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24       r      Place random planet
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26       u      Undo (undoes last planet insertion)
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28       e      Reset to empty universe
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30       g      Go Back (goes back to just after last planet insertion)
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32       Mouse  Click on a planet to delete it
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34   Physics
35       b      Toggle bounce (experimental)
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37   Display control
38       Cursor keys
39              Panning
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41       c, Space
42              Move display to center of mass
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44       x      Initiate center of mass tracking
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46       =      Zoom in
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48       -      Zoom out
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50       p      Toggle Pause
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52       o      Change all colors randomly
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54       t      Toggle Trace
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56       d      Double Trace Length
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58       h      Halve Trace Length
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60       Mouse  Drag a box around a set of planets to follow the center of  mass
61              of those planets
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63   Program control
64       H      Display help dialog
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66       k      Display option dialog
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68       Ctrl-Shift-k
69              Toggle  kid-mode.  Kid mode locks the keyboard and mouse, so the
70              only way to get out is to toggle kid-mode again to get out.
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72       l      Load Universe After pressing l, press  any  other  character  to
73              load  the  universe  with  that  name.  Universes  are stored in
74              ~/.planets/ .
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76       s      Save Universe After pressing s, press  any  other  character  to
77              save  the  universe  with  that  name.  Universes  are  saved in
78              ~/.planets/ .
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80       q, Esc Quit
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TECHNICAL DETAILS

83       Planets uses a fourth-order runge-kutta approximation for  the  simula‐
84       tion  itself.   Planet bouncing is achieved by adding a repulsive force
85       to planets at close quarters.  Planets  is  fairly  flexible:  you  can
86       change  the  gravitational  constant, the time-slice of the simulation,
87       and even the exponent used in the  gravitational  law.   Universes  are
88       saved  in  the  ~/.planets directory, and are simple human readable and
89       editable files.
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BUGS

92       Currently bouncing doesn't work very well unless  you  make  the  time-
93       slice  quite small.  Ideally, it would be nice to have a billiard-style
94       bounce system, but it's not clear how to  do  this  accurately  in  the
95       presence of a strong gravitational field.
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AUTHOR

98       Planets  was  written  by Yaron M. Minsky <yminsky@cs.cornell.edu> as a
99       gift for his nephew, Eyal Minsky-Fenick.
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101       This  manpage  was  contributed  originally  by   Martin   Pitt   <mar‐
102       tin@piware.de> for the Debian GNU/Linux system (but may be used by oth‐
103       ers).
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107                                April 20, 2003                      planets(1)