October 7, 2019
On the day you were born, the universe was already ancient beyond measure — and yet, in all those billions of years, it had never once...
Io Eclipse Shadow on Jupiter from Juno
Birthday · October 7, 2019
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APOD published October 7, 2019. Full image credits are on the original APOD entry below. A publication-date match, not a photo taken on your date. Independent of NASA.
What's that dark spot on Jupiter? It's the shadow of Jupiter's most volcanic moon Io. Since Jupiter shines predominantly by reflected sunlight, anything that blocks that light leaves a shadow. If you could somehow be in that shadow, you would see a total eclipse of the Sun by Io. Io's shadow is about 3600 kilometers across, roughly the same size as Io itself -- and only slightly larger than Earth's Moon. The featured image was taken last month by NASA's robotic Juno spacecraft currently orbiting Jupiter. About every two months, Juno swoops close by Jupiter, takes a lot of data and snaps a series of images -- some of which are made into a video. Among many other things, Juno has been measuring Jupiter's gravitational field, finding surprising evidence that Jupiter may be mostly a liquid. Under unexpectedly thick clouds, the Jovian giant may house a massive liquid hydrogen region that extends all the way to the center.