 Orbit Help Index

How To ...

Plot Trajectories

Commands

File menu

Action menu

Help menu


File menu commands

The File menu offers the following command:

Exit	Exits Orbit.


Action menu commands

The Action menu offers the following command:

Compute	Computes and plots the trajectory of a small object around a black hole


Help menu commands

The Help menu offers the following commands, which provide you assistance with this application:

Help Topics	Offers you an index to topics on which you can get help.
About	Displays the version number of this application.


File Exit command
Exit command (File menu)

Use this command to end your Orbit session.  You can also use the Close command on the application Control menu.  Orbit prompts you to save documents with unsaved changes.

Shortcuts

Mouse:	Double-click the application's Control menu button.

Keys:	ALT+F4


Plot trajectory of a small object around a black hole

If you select "Compute" from the "Action" menu, a dialog box for data entry will appear. The units are chosen for convenience: the Schwarzchild radius is the unit of length, the speed of light is 1, and the rest mass of the object (if it has a rest mass) is 1. The following aspects of the computation can be entered in the dialog box.

Starting momentum	Enter the starting momentum of the object.
Starting distance from center	Enter starting distance from the center of the black hole. For example, 0.5 means the starting point is halfway inside the black hole because in the distance unit chosen here the Schwarzchild radius is 1.0. The starting point will be marked by a small red circle. The Schwarzchild horizon is shown as a green circle.
Launch angle from radial direction	Enter the angle of launch with respect to the outward radial direction (in degrees).
Screen width in Schwarzchild units	Enter the scale of the drawing by entering the width of the screen in number of Schwarzchild radii.
Initial mesh width	Enter a smaller value for greater accuracy. However, choosing the default value is okay as the computation algorithm automatically changes the mesh width to maintain high accuracy.
Maximum tolerable error	Enter a smaller value for greater accuracy. However, choosing the default value is okay for most purposes.
Maximum # of points	Enter a larger value for a longer trajectory. The default value is good for most purposes.
Point plotting delay	Enter (in milliseconds) delay time between plotting points. This slows down the plotting to allow one to see the trajectory grow. To stop plotting click the right mouse button.
Particle type	Choose non-zero rest mass for objects like spaceships. Choose zero rest mass for photons (light).


Index command (Help menu)

Use this command to display the opening screen of Help.  From the opening screen, you can jump to step-by-step instructions for using Orbit and various types of reference information.

Once you open Help, you can click the Contents button whenever you want to return to the opening screen.


Using Help command (Help menu)

Use this command for instructions about using Help.


About command (Help menu)

Use this command to display the copyright notice and version number of your copy of Orbit.


Help Using Help Command
Context Help command

Use the Context Help command to obtain help on some portion of Orbit.  When you choose the Toolbar's Context Help button, the mouse pointer will change to an arrow and question mark.  Then click somewhere in the Orbit window, such as another Toolbar button.  The Help topic will be shown for the item you clicked.

Shortcut

Keys:	SHIFT+F1