http://space.jpl.nasa.gov/cgi-bin/wspace?tbody=599&vbody=399&month=4&day=9&year=2007&hour=14&minute=00&rfov=120&fovmul=-1&bfov=50&porbs=1&brite=1

That is Jupiter as seen from Earth on April 9th, 2007 at 14:00 UTC (I don’t know when the data was recorded by Hubble, but based on the simulator output, it must have been around that time.)

For Algirdas, and other people wondering about the “poodle spinning about about the elephant’s ankles”, remember that the axis of both Earth and Jupiter are inclined with respect to the ecliptic. The JPL simulator output displays a line along Ganymede’s orbit, which makes the effect of the axial tilt quite clear.

But can anyone answer my questions please :

1) Which is the solar system’s largest moon – Ganymede or Titan?
(Various sources keep saying one or the other but still not sure which.)

2) Is the answer to (1) affected by whether or not you count Titan’s atmosphere?

&

3) Does density / mass make a difference here? Ie. is Ganymede larger but Titan more massive or vice-versa?

Answers anybody? Please?

I must admit i wasn’t familiar with what Ganymede looked like before seeing the video, what i mistakenly saw as a specular highlight (as in, light reflected from a light source to the viewer on a shiny surface) is indeed a large whitish spot on the moon that i can now see on other pictures. DUH
Thanks a lot for your explanation, it makes perfect sense, it’s just that, ‘intuitively’ speaking (for someone who really doesn’t know much about astronomy / astrophotography) the video felt fake… a good example of how one can fool himself when he doesn’t know much about something!

I’m not sure what you mean by this highlight that looks fake. I thought it looked pretty much like every other photo of Ganymede I’ve seen.

As for it not changing, let’s do some math. First, remember that Ganymede–just like Earth’s moon–is tidally locked to the planet it orbits. In other words, Ganymede always shows the same face to Jupiter. In other other words, its orbital period of 171.75 hours is also its rotational period. The video was compiled from pictures shot over a 2 hour period. Ganymede appears in about 14 seconds of that 18 second video (I was too lazy to get an exact frame count for the moon), meaning that we’re seeing Ganymede for (14/18)*2hours = 1.6 hours (roughly). Since Ganymede’s rotational period is about 172 hours, what you are seeing in the video, is about 0.9% of Ganymede’s rotation.

Do you really think that you would be able to see a less than 1% rotation? (hint: In the high definition video, Ganymede’s diameter is only 50 pixels.)

this looks totally fake to me. I already got the feeling that something was wrong when looking at the picture in a previous post, but it’s even more obvious in the movie: what’s that specular higlight showing up on Ganymede ??? (it looks like a marble ball…)
when you look at the HD version you can see Jupiter spinning (rather quickly) yet ganymede doesn’t change *AT ALL* except for the translation motion.
To me this look like something made in 5 minutes with 3D studio or Maya, wouldn’t be surprised if it turns out to be an hoax.