Planetary Moon orbits and times need some work

[David Knisely]

In both the regular downloaded version and the new pre version, the orbital times of events differ from what they are supposed to be in reality, sometimes by up to 40 minutes. I have been checking the events of the Galilean moons of Jupiter, (eclipses, planetary occulations, transits, ect.) and they are off by from 15 to 23 minutes or more on Io and Ganymede. Also, the ealier release had Callisto casting a shadow onto Jupiter, and at the current position and tilt of the orbits with respect to the sun this year, I don't think that is possible. The orbits of the moons definitely need a lot of work here. One thing to also remember is that, if you are observing these events from a distant point in the solar system, the speed of light *must* be taken into account when computing the times for positions and locations.

[chris]

In both the regular downloaded version and the new pre version, the orbital times of events differ from what they are supposed to be in reality, sometimes by up to 40 minutes. I have been checking the events of the Galilean moons of Jupiter, (eclipses, planetary occulations, transits, ect.) and they are off by from 15 to 23 minutes or more on Io and Ganymede. Also, the ealier release had Callisto casting a shadow onto Jupiter, and at the current position and tilt of the orbits with respect to the sun this year, I don't think that is possible. The orbits of the moons definitely need a lot of work here. One thing to also remember is that, if you are observing these events from a distant point in the solar system, the speed of light *must* be taken into account when computing the times for positions and locations.

Celestia does not currently take light time into account, which means that the times of events of the Galilean satellites are generally off by ~40min from times quoted in almanacs. I'll get to this eventually, but it's going to require some architectural changes in Celestia to make it efficient.

Other innaccuracies are due to the fact that the satellite positions are relative to Jupiter's equatorial plane, which I haven't quite gotten right yet. I'm still trying to figure out what's wrong here . . .

Callisto does cast shadows on Jupiter this year. In fact, right around now Jupiter's equatorial plane is seen almost edge on and mutual phenomena of the Galilean satellites are visible. The 11 Nov 1997 triple eclipse of Jupiter can be recreated in Celestia, so the positions of the moons are that far off . . . Still, I won't be really satisfied until I get positions accuration to +/- 10km.

--Chris