A couple of months ago I wrote about watching an eclipse of Europa by Jupiter's shadow. It's a game I call "Whac-a-Moon", where a moon comes out from behind Jupiter, but stays there for only a short time then disappears into eclipse. If you aren't ready for it, it's gone.
This can only happen when Jupiter's shadow is offset from Jupiter that there's a gap between the planet and the shadow as seen from Earth. Jupiter is getting low in the west, and soon we'll lose it behind the sun, but tonight, Wednesday May 8, there's a decent Ganymede Whac-a-Moon opportunity for those of us on the US west coast.
Ganymede disappears behind Jupiter at 6:45 pm PDT, still during daylight. Some time around 9:43 Ganymede reappears from behind Jupiter, but it only stays visible for a couple of minutes before entering Jupiter's eclipse. Don't trust these times I'm giving you: set up at least five minutes early, preferably more than that. And set up somewhere with a good western horizon, because Jupiter will be very low, less than 8 degrees above the horizon.
So far, I've only watched Europa as it slid into eclipse by Jupiter's shadow; I haven't whacked Ganymede. But Ganymede is so much larger that I suspect the slow dimming effect will be even more obvious. Unfortunately, I'm not optimistic about being able to see it myself; we've had cloudy skies here for the last few nights, and that combined with the low western horizon may do me in. I may have to wait until autumn, when Jupiter will next be visible in our evening skies. But I hope someone reading this gets a chance to see this month's eclipse.
[ 11:46 May 08, 2013 More science/astro | permalink to this entry | ]