Ganymede or not Ganymede

[safcjames]

Hi all, looking for a bit of advice here if someone would be so kind. With astonishingly clear skys over here in Germany we spent a large portion of our time out with the telescope focusing on objects that we wouldn’t otherwise get a chance to see in such clarity but we did reserve a bit of time for one of our old favourites, Jupiter. Visibilty and clarity were great but seem to have posed us with an issue. The usual 4 moons were (so we thought) easily visible however we also had a reasonably well defined object at the extreme bottom left of the planet very close to it, in fact, so close it appeared through the telescope to be touching the planet.

With a bit or research this morning I am inclined to believe that this was actually Ganymede just coming out of the dark side of the planet on its usual orbit but if that is so then what did we see as a 4th moon where we thought we had seen Ganymede? Or, if it wasn’t Ganymede that seemed to be so close to the planet does anyone have any idea what it could have been?

This has us baffled so any ideas would be welcome

[DirkSteele]

Just ran a simulation of Jupiter and its moons for this morning and I think it was actually Europa just appearing.

[Matt Scunthorpe]

Ive never looked at the movements of the moons before, this is something im definately going to have to try one night.

[safcjames]

@ DirkSteele, thanks for the help with this. So Europa and not Ganymede then. Either way this is an absolute first for me, seeing a moon so close to the planet on its orbit and it still has me acting like a kid at Christmas Could I also ask what software you used to simulate this? I would love to be able to identify the other objects we had in the lense also because we still have (to us) an unidentified object. We were sure we had Europe, Ganymede, IO and Castillo all in the lense with this 'fifth' object very close in. Clearly one of these is an imposter

@ Matt, looking at the movement of the moons was something we really didn't plan but will be going back to. We actually planned the night for Kemble's Cascade, Uranus and a little later the first clear night since the return of Orion (we have never tired of the nebula). Jupiter really was a last minute after thought last night otherwise we would have spent more time watching the progress of our new found little friend.

[Tinker1947]

Stellarium will show you whats in view and can be taken back to your viewing time...

[safcjames]

clearly a blond moment for me then I have Stellarium installed at home and never even thought to check with it.......

Thanks for all the help again guys. Can't wait to get home tonight now and check it out

[Qualia]

Ay, I think Dirk is right. A handy program you might like in the future, Safcjames, is this which plots the moons for easy reference.

[safcjames]

I think I may have this solved now. Just broke every rule for or company network and installed Stellarium on my laptop I think we were looking a little earlier than Dirk ran the simulation for and we were actually seeing IO just approaching its orbit directly in front of the planet, just before it started casting its shadow. When we were looking Europa was already at the extreme 7 O'clock position.

Again though, really thanks so much everyone for helping out the new guy.