Tonight, the shadows of three of Jupiter's four largest moons will fall on the giant planet at the same time -- a rare event that won't be visible again in American skies until December 2032.
Jupiter is the largest planet in our solar system and has more than 60 confirmed moons.
It's not unusual for backyard astronomers to see some of the larger ones cast a shadow across the surface of the gas giant, but seeing the shadows of two moons at once can feel like cause for minor celebration. Triple-shadow transits are even less common, of course, and they only happen once or twice a decade on average, writes amateur astronomer Bob King in Sky and Telescope.
Here in Los Angeles, Jupiter will rise in the night sky at 6:22 p.m. PST, but the show really begins at 7:11 p.m., when the shadow of Callisto begins to cross the disk of Jupiter. Callisto is the third-largest of Jupiter's moons and only slightly smaller than Mercury.
At 8:35 p.m., Callisto's shadow is joined by Io's shadow. Io is a bit larger than Earth's moon and the most volcanically active body in the solar system.
The triple part of the triple transit starts at 10:27 p.m. That's when Europa's shadow joins the other two. Scientists think Europa may have a liquid ocean beneath its icy crust, making it one one of the best places to look for life in the solar system.
The three shadows are on the moon simultaneously for just 25 minutes, until 10:52 p.m. After that, the shadow of Io is no longer visible.
If you don't have a telescope and you live near Los Angeles, you can head over to the Griffith Observatory to see the celestial clockwork of Jupiter's moons and their shadows through telescopes set up by the Los Angeles Astronomical Society and the Planetary Society.
If that's not an option, you can watch the whole thing live, online, using the live video link above. Griffith Observatory is streaming video of the event from 8:30 p.m. to 11 p.m.
Happy sky watching!
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