One of the reasons I find Twitter so useful is that through the people I follow all over the world, I find out about cool things that I may never had heard of by any other means. Today's example: a nice little animation of a rotating Jupiter and moving Io, shot by Pleiades-1B. (Thanks to Daniel Fischer for the tweet.)
What's Pleaides-1B? It's a French Earth observation satellite that's intended to perform very high-resolution (50-centimeter) imaging of nearly any location on Earth with a daily cadence. It was launched on December 2.
The two Pleaides-1 spacecraft are described as being unusually "agile", in that they can do highly accurate off-nadir point-and-shoot imaging of targeted locations. As one step in Pleiades-1B's calibration and commissioning, it is being pointed at more than 1000 stars -- once again, as they have been for millennia, we steer our ships by the stars. This observation of Jupiter was commanded as part of the commissioning phase.
I did have trouble figuring out which moon was in the animation, because the times given in the caption to the image don't quite match up with reality. It states December 7 between 1300 and 1800 GMT, but the first frame has a moon hidden behind the globe, which then comes out from behind it in the second frame. Io did that at roughly 0939 on December 7. Adding 33 minutes of one-way light time doesn't get me all the way to 1300. It has to be Io, because other moons would appear farther above Jupiter's equator, so I know I have the moon identification correct.