Of all the amazing things I plan to look at through my future telescope (yes, I’m still saving), this event didn’t even cross my mind. Not surprising really, it’s probably never been observed before: Io’s whole shadow transiting across the large Jovian moon, Ganymede.
But on August 16th, that changed when Christopher Go from Cebu, Philippines used his 11-inch Celestron telescope to capture the sequence of events as Io passed in front of the Sun, casting a near-perfect shadow on the large moon of Ganymede. If you were standing on Ganymede’s surface, looking at the Sun, you would have seen an Io solar eclipse.
My favourite thing about this animation is that both moons are very detailed, even at this resolution. You can see mottled shades on Ganymede, and I think the spin of Io may even have been captured.
A wonderful testament to Christopher Go’s astronomy skills and a fantastic example of how advanced our amateur astronomical equipment is becoming…
UPDATE: It turns out that little Io is getting its own back for last July’s eclipse by Ganymede, plunging the smaller moon into darkness. In the following video by OccultDave on YouTube, over a period of about 16 minutes, Io (the dot to the far-right) dims dramatically as Ganymede (the dot in the middle, next to the bright disk of Jupiter) blocks the sunlight: