Jupiter’s moons are at it again.
Last week, on August 26-27, you had a chance to see a double shadow on the face of Jupiter, cast by Ganymede and Europa. I had the good fortune to see this event, and it was a splendid sight (though I’m still paying for the sleep deprivation… a busy schedule makes it hard for your humble publisher to catch up on sleep).
But this week, on September 2-3, you’ll see the extraordinary sight of Jupiter with NO moons. Ganymede and Europa will once again pass in front of the giant planet, while Io and Callisto will pass behind Jupiter from our point of view, making it nearly impossible to visually detect any moons around Jupiter.
From the Americas, this event occurs from 4:43 to 6:29 Universal Time, which is 12:43 a.m. to 2:29 a.m. (Eastern Daylight Time) on the morning of Thursday, September 3. Here’s a diagram to show the path of the moons around the planet…
A diagram of the orbits of Jupiter’s moons in early September (from Sky and Telescope).
Surprisingly, this is the last time this event happens until 2019.
And just like last week, you may briefly see a double-shadow on the face of Jupiter as Ganymede and Europa move across the face of the planet.
And if you think Jupiter without moons is a strange sight, how about Saturn without rings! This beautiful planet is oriented such that the rings are edgewise to Earth on September 4, and were edge-on to the sun earlier in August. This last occurred in 1996, and won’t occur again until 2025. But sadly, Saturn is lost in the sun’s glare and can’t be seen this month.