Moon far away from its trajectory

lidocorc · Post #1by **lidocorc** » 28.01.2008, 20:50

The normal vector of the moon's orbit plane is not stable. It precesses slowly. Once Celestia has drawn the moon's trajectory (watch it in follow mode, earth focussed), Celestia doesn't update it. As a consequence the moon goes off its trajectory up to more than 10 times its own radius.

This is certainly not due to the kind of interpolation of the trajectory between points. It's because these points are not being updated.

It would be great, if this feature could be improved in future versions.

Sorry, if I overlooked any contributions on that in the forum.

bdm · Post #2by **bdm** » 28.01.2008, 22:51

What version of Celestia are you using?

lidocorc · Post #3by **lidocorc** » 29.01.2008, 18:13

bdm wrote:What version of Celestia are you using?

Celestia 1.5.0 final.

Post #4by **chris** » 29.01.2008, 18:30

lidocorc wrote:
bdm wrote:What version of Celestia are you using?

Celestia 1.5.0 final.

Trajectories don't get updated constantly because the orbit calculations can be very computationally expensive, and you need > 100 of them for a trajectory. It's not necessary to update the entire trajectory every frame, but it would be if the time rate was set very high.

An alternative to updating the trajectory is to show an ellipse for the Moon's (or other body's) orbit based on its osculating elements at the current time. The Moon would always be exactly on the trajectory, and you'd get a very good sense of how the Moon's orbit evolves over time.

--Chris

rbroberts · Post #5by **rbroberts** » 04.02.2008, 02:26

I'm running into this as a problem. I'm putting together a tutorial on eclipses for the upcoming Feb 20 lunar eclipse and noticed that as I run time forward and backward at high rates to show the past few years of eclipses, that the moon quickly leaves its nominal orbit. Stopping time and turning on and off the orbit doesn't force a recalculation, so....

Is there any way to get celestia to recalculate the orbit?