Wait, is that black hole devouring Jupiter? No worries. It’s the shadow cast by the moon Io. Io is one of Jupiter’s four largest satellites with a diameter of 2,264 miles (3,644 km), only a hundred miles bigger than our own moon. What makes the photo so striking is the perspective. NASA’s Juno spacecraft took the photos up from up close and at a unique, inclined angle on Sept. 12.
Juno orbits Jupiter every 53 days on an orbit that takes it over the planet’s poles. As it swings over one pole and under the next it can look down on the planet and see it from perspectives impossible on Earth. We’re locked into one view because Earth and Jupiter lie in nearly same plane like the other planets. The solar system is a like a race track with a runner in each lane. The runners can only look across at the other runners and never see each other from above or below. Juno has a birds eye view.
Viewed from Earth the moons occasionally pass in front of Jupiter and cast inky-black, pinpoint shadows on its clouds. Astronomers call the events shadow transits. Out at Jupiter, if you found yourself orbiting beneath Io’s shadow you could look out the window and see a total eclipse of the sun. All four of Jupiter’s bright moons cast shadows visible in small telescopes from 4-inches on up. We see them as small dots, but Juno’s got a front row seat, making the shadows most impressive.
How would you like to see the shadow of Io in your own telescope? You can on Friday evening September 20 between about 7:40 p.m. and 9:56 p.m. Eastern Time (6:40 and 8:56 p.m. Central and 5:40 and 7:56 p.m. Mountain). Jupiter will be the bright “star” low in the southwestern sky at dusk. Sometimes the “thick” air at low altitude can blur the view, but in good conditions using a magnification of about 100x the poppy seed-sized shadow will appear along the northern edge of the North Equatorial Belt, one of two prominent dark cloud belts that resemble tire tracks. Be patient, focus carefully and you should be able to see it. The shadow-caster, Io, will shine to the west just off the planet’s edge.
If you live in or near Duluth and the sky is clear Friday night (Sept. 20), stop by Amity Coffee (4429 E. Superior St.) where telescopes will be set up to view the planets and shadow transit — weather permitting — as part of the Celebrate the Night Sky Week. For details and updates, click here.
And now it’s time to see the little moon casting all these shadows — Io. It’s unique in the solar system with a molten interior, continuous volcanic eruptions of sulfur-laden lavas and a lovely pizza-like orange and red color. Io internal heat and powerful vulcanism is a result of being squeezed this way and that by Jupiter’s powerful gravity during its 42-hour orbit. The flexing heats the moon interior which releases the pent-up energy in the form of active volcanoes.
Release some of your pent-up energy by getting that scope out for a look.
*** For more about amazing things in outer space — real and imagined — check out my new book titled Urban Legends from Space from Amazon, Barnes & Noble and Indiebound currently available for pre-sale at a nice discount.