Celestia Forums

I just can't seem to get the orbit in right. It either is in the path of Earth or Venus or is way out by Pluto. Any ideas? I thought Period defined how far a planet was from the sun, but maybe I'm wrong?

The Period is how long it takes to orbit the sun in Earth years. The SemiMajorAxis is how far it is on average from the sun in astronomical units, the average distance from the sun to Earth.
They are related by Kepler's third law, P^2 = a^3 for units normalized to Earth years and AU. For usual units, it is P^2 = ( 4*(pi^2)/( G*(m1+m2) ) ) * a^3. P is the period and a is the semimajor axis, m1 and m2 are the mass of the orbiting body and the body it is orbiting and G is the gravitional constant.

so I should be editing the semimajoraxis then?

Set the SemiMajorAxis to put the orbit where you want it

and set Period to be sma **1.5
(i.e. Period = sqrt(sma^3) )

so that it takes the right amount of time to go around the Sun.