# Getting started with planets

A quick tutorial to get you started

### Adding planets:

Press "a" to add a planet. That will attach a circle to your pointer, indicating the size of the planet. That size can be changed by pressing a number 0-9, and can also be adjusted up and down by a small percentage using the up and down arrows.

You click once to place the planet in a given location. Then move the mouse again, and you'll see a vector pointing from the planets location to the pointer. This is the initial velocity. Click again to set this.

Note that you can simply double-click to make a zero-velocity planet.

### Keeping planets on-screen

There are a few ways of preventing planets from disappearing from view. You can:

recenter
  on the center of mass and zero out the central velocity, by pressing the space bar.
pan
  to follow the planets, by using the arrow keys
zoom in/out
  by using the +/- keys. If you think you've lost planets, you can zoom way out, and eventually you'll seem them again. Just press the - key and hold it.

### Saving and loading universes

You can save a configuration by typing "s" and then any other single character. Type "l" and that character to load the universe. Try l9 to load an interesting universe that comes with the distribution.

### Fun things

undo and goback
  "u" undoes the last planet addition, which is good for fixing mistakes. "g" goes back to just after the last planet addition which is nice for replaying interesting situations. You can undo arbitrarily many steps.
control panel
  Press "k" to call up the control panel. This lets you see and control a number of configuration options, and see some of the state of the system.
Traces
  Press "t" to toggle tracing, "d" to double trace length, and "h" to half trace length
Bouncing
  Press "b" to toggle force bouncing, and "B" to toggle true bouncing
C-O-M following
  You can track the center of mass of a subset of planets by dragging a box around them. "x" cancels the COM tracking. This is useful, for instance, if you want to track the moon and earth only of a moon-earth-sun system.

More information can be found in the Keybindings.txt file in the distribution.

Last modified: Mon Jan 7 11:21:44 EST 2002