Celestia Forums

Hi user group,

I discovered Celestia a week ago, and I've found myself playing around with a lot for fun. I have some questions on the inner workings of the program. I suppose I could download the code and look at it, which I will probably do sometime, but asking a question here is probably easier.

How are the planeyary obits generated? Is from celestial mechanics first priinciples, i.e. from using a full (say) Runge-Kutta solution of the coupled differential equations? Or is it based on some perturbation approximation?

How well do the orbits tally with (say) detailed ephemerides ?

It's a great program!

Best regards,

s?ren molander

s?ren,

Celestia does not include any gravitational calculations. Instead, it uses the VSOP87 theory to position the planets. (The appropriate one is invoked by a CustomOrbit declaration in solarsys.ssc.) The VSOP87 polynomials include enough of the relevant gravitational effects to make them accurate for most of the planets to better than one arc second (as seen from the Earth) from about 1000 BC to 3000 AD.

Ref:

Bretagnon P., Francou G., : 1988, Astron. Astrophys., 202, 309.

Can Celestia be used to simulate what would happen if new bodies were introduced to an orbiting system - example, what if the moon were 10% closer to earth. Or, what if the moon was suddenly removed?

Can Celestia be used to simulate what would happen if new bodies were introduced to an orbiting system - example, what if the moon were 10% closer to earth. Or, what if the moon was suddenly removed?

No, because it doesn't use the pre-mentioned Runge-Kutta routine or any other gravitational simulation routine. If you want to simulate stuff like that, you can use Gravity Simulator. (http://www.gravitysimulator.com). There's no fancy graphics, everything is just pixels and plain circles, but you can suddenly remove the moon if you want. Or move it, or add additional moons with your own custom masses.

Thanks very much !

Hi Tony,

are you [the|one of the] developer/s of that program?

maxim

Hi, Maxim. Thank you for asking. Yes, I wrote the program and I am the webmaster of the site. Let me know if you have any questions.

It would be nice if Celestia did calculate orbits, but sadly, to do it accurately, it would take a lot of power...