This simulation is the simplest simulation of interest - a two body system with one body orbiting the other in an eccentric orbit.
It is mainly useful for familiarizing yourself with AstroGrav's facilities and some of the astronomical concepts necessary to get the maximum benefit from AstroGrav.
Kepler's Second Law - use Evolve / Run Forward to set the system running, and see how the planet speeds up as it approaches the star, reaches its maximum speed when it is closest to the star (as it crosses the positive x-axis), and then slows down again as it recedes from the star. Using Window / New View to open a second view window will show the situation from a different viewpoint which may make the situation clearer. If you double-click on the planet, you can then edit the planet's eccentricity, and experiment with evolving the system with different eccentricities.
Orbital Elements - use File / Revert to Saved to restore the original system, and then double-click on the planet to open its editor window. Try editing one of the orbital elements and accept the change to see its effect in the view window. Then repeat this process several times, each time editing a single orbital element, and seeing the effect in the view window. This should help to give you an intuitive feel for the orbital elements, and for editing a system to create any desired effect.
Stroboscope Effect - use File / Revert to Saved to restore the original system, and then use Evolve / Settings... to change the time step to 10 years - the planet's period. If you then set the system evolving, you will see that the planet appears to be stationary because at the end of each time step the planet has completed an entire orbit and returned to its original position. Now use Evolve / Settings... to change the time step to 9.9 years - slightly less than the planet's period. If you then set the system evolving, you will see that the planet appears to be moving backward because at the end of each time step the planet has completed slightly less than one orbit.
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