MAIN MENU Move the highlight with the arrow keys then make a selection with the ENTER key. MASS Enter the mass of the planet in Kilograms (Kg). The number given must be greater than or equal to zero. DENSITY Enter the density of the planet in Kilograms per cubic Meter (Kg/M^3). The value given must be greater than zero. The density of water is 1000 (1E03) Kg/M^3. X POSITION Enter the X position of the planet in Meters. Y POSITION Enter the Y position of the planet in Meters. X VELOCITY Enter the X component of the velocity in Meters per Second (M/s). Y VELOCITY Enter the Y component of the velocity in Meters per Second (M/s). ORBITS This field enables plotting of the orbit dots that mark the path of the planet as it moves. The dots will only display if the Show Orbits setting under the Misc menu is ON. Valid values for this field are Y and N. STATIONARY This locks the planet firmly in place. New position values are not calculated for stationary planets. This is an imaginary condition and should not be used if you are modeling an actual system. ZOOM POWER Changing the zoom power allows you to "Zoom-in" and "Zoom-out" to view orbit- ing bodies at varying magnifications. To zoom-out and see the whole system, use small values. To zoom-in and make objects appear very big, use larger values. This value is also changeable from the running simulation by using the PgUp, PgDn, and Home keys. X CENTER This is effectively a panning value. You enter where in space you would like the center of the screen (X direction) to show. This value is also changeable from the running simulation by using the arrow keys in conjunction with PgUp and PgDn. Y CENTER This is effectively a panning value. You enter where in space you would like the center of the screen (Y direction) to show. This value is also changeable from the running simulation by using the arrow keys in conjunction with PgUp and PgDn. TIME INTERVAL Time Interval is how long a force acts on a planet in seconds, or in other words, the elapsed time between new velocity and position calculations. The planet motions are simulated not by curves, but by many very short lines. The time interval relates to the length of those lines. Since in reality they are 0 in length, the smaller this number the better. You may lower this number for accuracy, or increase it for speed. If the planets are not moving more than a few pixels per plot, depending on how sharply curved the planet path is, the accuracy you are getting is probably fine. This value can be automatically determined with the Dynamic Time Interval function ('D' on the simulation screen). GRAVITATIONAL CONSTANT The gravitational constant is the strength of the gravitational field. You should not need to change this value, but it is included for versatility. Changing it will affect the units used for mass, density, distance, and velocity. The value of +6.67E-11 is the actual value found in reality. CALCULATIONS PER PLOT Actually a bit of a misnomer, this really relates to Plots per Calculation. It only affects the frequency of plotting positions on the screen, not how the calculations are done, or the paths planets will take. You may want to change this when you are watching the Status Line, or if you have very slow display hardware. CENTRAL PLANET TRACKING You can watch the simulation from the perspective of any one of the defined planets. This will plot the specified planet in the center of the screen and the other planets will move in relation to it. This does not affect how the calculations for move- ment are performed, only how the planets are disp- layed. Using this, you can follow the orbit of one system which is part of a larger system. For instance, you can watch the earth-moon system up close while it revolves around the sun without having to do zoom/pan/zoom/pan/etc. An entry of 0 will turn off this feature. This function is also available from the running simulation by pressing first the 'C' key, and then the key for the planet you want to track (1-9, ! @ # $ % ^ &). STATUS LINE Displays the current status of a planet. Values displayed include: Planet number, Mass, Position, and Velocity. If the planet collides with another, the status switches to the live planet. A value of 0 turns this function off. This function is also available from the running simulation by pressing first the 'S' key, and then the key for the planet you want the status displayed for (1-9, ! @ # $ % ^ &). SAVE FILE Enter the full drive, path, and name of the file you want to save to. If you omit the path, the current directory is assumed. If you omit the extension, .GRV is appended. RESTORE FILE Enter the full drive, path, and name of the file you want to read from. If you omit the path, the current directory is assumed. If you omit the extension, .GRV is appended. Answer with the Y or N key.