Celestia Forums

Ver: 1.3.1 pre6

Galileo's orbit seems to be doing a hop-scotch on Jupiter's orbit.

Here is a cell: URL to demonstrate...



Is this for real?

-Don

a) the lines drawn to illustrate the orbits aren't as accurate as one might like. See the "user's faq"

b) the accuracy of Gallileo's xyz trajectory also depends on how many samples there are in a given time interval. To see if Galileo's model is following the correct path at any given time, you'll have to watch it close up and compare its position with Horizon's record for that epoch. If you decide that the default low resolution trajectory provided with Celestia isn't good enough for whatever events you're trying to model, you need to download an approprite trajectory segment from Horizons. Jack Higgens has provided some examples on his Web site and some are on mine.

(added later)
c) I'll admit I would have expected Galileo's trajectory to show loops (its orbital speed around Jupiter should be greater than Jupiter's orbital speed around the Sun) but my guess is that the samples made for drawing the path aren't close enough together for them to show up. Only Chris can say for sure, though.

Thank you Selden.

I believe what you're seeing is the actual path of Galileo. But remember, you're seeing it in a heliocentric reference system. The drawings you usually see of Galileo's orbit show it in a reference system centered on Jupiter with a fixed solar direction.

- Hank

I once tried getting jovicentric elements for galileo- but that doesn't show the orbit well either... because of the number of orbits, the smooth orbit lines just turn into right angles close to the planet & on small orbits...

Because its orbit is highly eccentric, Galileo moves very fast (relative to Jupiter) when it's close to the planet. So equally spaced (in time) sampling will cause the orbit to appear poorly fit near perijove.

- Hank

Thanks for adding some Astro-knowledge to this old brain of mine!

Interesting information and discussion, to me. Things I never even thought of ... probably because I'm not an astronomer ... just love looking up at the stars out here in the country.

-Don