**Quote from Mal on 10/28/06 at 14:45:41:**

So at each timestep (e.g. 16k), you plot the position of the planet on its orbit. That way you end up with a bunch of dots that follow the orbit showing the planet's location at that time. They should be spread furthest apart at perihelion, and closest together at aphelion.

Basically I'm after a plot of one orbit's worth of points - how the orbit moves in space isn't relevant to this.

That's what the T (trails) button does. It appears that it is tracing the orbit, but it is only plotting points. The spacing between the points it plots are usually less than a pixek, giving the appearance it is drawing a continuous curve.

Here's the inner solar system at 16K time step zoomed in enough to see the pixels representing each planet's position at each time step. You can even follow the moon as it orbits the Earth (blue).

In regards to the argument of perapsis converging on a value, I think I know why. Consider that a perfectly circular will have no periapsis. If it's a circle, there is no close point.

Now consider the longitude of the ascending node. In an orbit whose inclination is 0, there is no ascending node. Ascending node is the point where it passes from below the ecliptic to above the ecliptic. In an orbit with 0 inc, the planet rides

*on* the ecliptic, never going above or below. So the node is undefined.

You're starting out with a round orbit with 0 inclination. Imagine standing on the North Magnetic Pole of Earth with a compass. The needle is spinning all over the place. It doesn't know which way to point. Same thing with Gravity Simulator's periapsisometer and ascendingnodometer (I just made up those words). You're asking it for the derivative of a non-differentialble point. It doesn't know which way to point, and its "needle" is swinging all over the place. But once small amounts of eccentricity and inclination are introduced into the orbit, the periapsis and ascending nodes become more clearly defined. You need enough eccentricity and inclination that these values rise above the background noise of the simulator, and the pertabutions generated on the planet by the secondary. (remember, the secondary also tugs on the Sun, complicating things and ensuring that your average eccentricity per orbit is not necessarily your instantaneous eccentricity at all points). The more ecc and inc, the better the number is defined, and your graph starts to converge on a value.