On the morning of May 12 (May 13 local time) at about 6.20am there was an occultation of Io by Europa. The close proximity of this event to sunrise caused a lot of seeing problems, and so the quality of the frames in the animation are not so good.
Io is approx 1" in diameter, and Europa is a litle smaller at 0.8".
I'll probably clean this up a bit later and add some captions etc.