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## Three-Body Integrator

Help File

## General Information

HELP. Displays this help screen. To exit, click one of the Exit Help buttons located at the
top and bottom of this screen.

## Integration Parameters

ACCURACY. This number specifies the accuracy of the
integration. More accurate integrations take longer and are more prone
to run into numerical problems. Accordingly, you want the lowest
number which gives an accurate plot. Experiment by following the same
orbit at different accuracies and seeing if the output plots are
similar.
INTEGRATION TIME. Here you specify how many years into the future
the orbit should be followed. Be careful in choosing this parameter as
it is directly correlated to how long you will wait before seeing a
plot! A good strategy is to try a short integration time first to get
an idea of how fast the program is.
SAVE FREQUENCY. This number determines how often a point along the
orbit is saved to disk. A larger number yields a more accurately drawn
orbit at the expense of plotting time and disk space. You want to
choose the largest number that yields a reasonably accurate
orbit. Experiment!

## 2 Bodies in Bound Orbit

MASS OF THE SUN. Here you specify the mass of the star around which
the planet will orbit. The mass is entered in units of Solar Masses. This
means that if you enter "1.0" the star will have the same mass as our sun. If
you enter "2.0" the star will be twice the mass of our sun, and so on...
MASS OF THE PLANET. In this space, you enter the mass of the planet which
will orbit the star. Again, you specify the mass in units of Solar Masses.
Some Examples of masses you could use:

Venus: 0.000002 Solar Masses

Earth: 0.000006 Solar Masses

Jupiter: 0.000954 Solar Masses

Saturn: 0.000286 Solar Masses

Uranus: 0.000044 Solar Masses

Neptune: 0.000051 Solar Masses

SUN TO PLANET DISTANCE. Here you specify the distance between the star and
the planet at pericenter. You enter this value in units of AU which are
define such that 1 AU is the average distance between the earth and the sun.
ECCENTRICITY. In this space, you enter the eccentricty of the planet's
orbit about the star. You must enter a value greater or equal to 0 but less
than 1. An eccentricity of 0.0 will produce a circular orbit. If the
eccentriciy is greater than zero the orbit will be an ellipse.

## 3rd Body (of Infinitesimal Mass)

3RD BODY IS NEAR. You may choose to put the 3rd body near either of the
two stable equillibrium points called Lagrangian Points. The Lagrangian
points lie in the plane of the planet's orbit about the star. They are
located at the tips
of equillateral triangles whose bases are formed by the line between the
star and the planet. The Leading Lagrangian Point is the equillibrium point
which is located ahead of the planet as it moves around in its orbit. The
Trailing Lagrangian Point is located behind the planet.
DISPLACEMENT FROM LAGRANGIAN POINT. Here you choose how far from the
Lagrangian point the third body will initially be placed. The coordinate
system in which this dispacement is specified is defined such that:

1. The center of mass of the system is at the origin.

2. The orbit of the planet about the star lies in the x-y plane.

3. Initially, the star lies on the negative x-axis and the planet lies on
the positive x-axis.
VELOCITY OF 3RD BODY IN ROTATING FRAME. Here you choose the intial
velocity of the 3rd body. This velocity is specified in the
Rotating Coordinate System. The Rotating Coordinate System is a coordinate
system which has its origin a the center of mass. The Rotating Coordinate
System rotates about the center of mass with an angular velocity equal to the
average angular velocity of the planet's motion about the star.

SUBMIT FORM. Send the parameters that you have chosen to the
orbital integration program!
LOAD DEFAULTS. Set all parameters back to their default values.

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