Celestia Forums

Hi all,

firstly thankyou to the guys that are responsible for this application and also to he guys responsible for bringing it to OSX - you have allowed me to be amazed and awestruck byt our fabulous solar system and indeed our galaxy, as well as so many of my friends too, so thankyou very much indeed.

I suppose I should note that Using a GeForce 4 4600 in my Dual Ghz PMG4 runs very well, except that as many others have said the orbits seem to play up when you get in close.

Can anyone tell me just how accurate the application is? I mean, I know the last Halley comet pass was in Jan 1986, and I followed Halley from 1970 and it was closest in 1986, so that was pretty amazing, but could you guys tell me just how accurate all this stuff is? Can I, for instance, find out the next time I'll be able to see Halley? (Although I might be pretty old then I think).

What about planet rotations? Are they all accurate too? And the spacecraft positions? If so, then you guys have floored me with your skills and perseverance.

Thanks once again,

-Peter

Most everything with in our solar system is accurate or near accurate, I have been on this forum for a while and have learned that the farther out the planets go, the more inaccurate they are (due to their distance from earth and the difficulty of gathering info on them). Though I really can't say which objects for sure are 'wrong'. If you have just started using Celestia, you may want to check out the download section of my site (look in my profile for the link) to get 'caught up' on all add-ons.

Welcome Pete

Some orbits, such as those of comets and asteroids, are modeled with simple Keplerian elements (that is, they are approximated as an ellipse, which isn't quite true because of gravitational interactions between different bodies). Others are modeled more precisely with a model based on actual solar system dynamics. The Earth probably has the most accurate orbit of anything in the database.

It's unlikely that Halley's comet could be accurately modeled for all times because comets are also affected by the gas jets that boil off of the nucleus every time they swing past the sun. It's as if there's a rocket engine on the comet that blasts away periodically in unpredictable directions. So predictions become inaccurate after a fairly small number of solar orbits, and then there are the interactions with the planets too. Halley's orbit seems to be modeled as a Keplerian ellipse in Celestia, so I wouldn't trust it for more than an orbit or two.

Other things are more inaccurate. Celestia (at least the Mac version I have) doesn't yet model the precession of the planetary rotation axes, so you won't see the way that the north celestial pole wanders away from Polaris over the millenia, though most of the rotation axes are accurately positioned now. Some of the moons of the planets have things like orbital phases more accurately modeled than others. But various people occasionally contribute fixes for these things based on the best available reference materials.