Astronomy Picture of the Day

    Discover the cosmos! Each day a different image or photograph of our
      fascinating universe is featured, along with a brief explanation
                    written by a professional astronomer.

                               2019 October 7

                   Io Eclipse Shadow on Jupiter from Juno
    Image Credit & License: NASA/JPL-Caltech/SwRI/MSSS; Processing: Kevin
                                   M. Gill

   Explanation: 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.

                 Tomorrow's picture: sprite lightning in HD
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       Authors & editors: Robert Nemiroff (MTU) & Jerry Bonnell (UMCP)
            NASA Official: Phillip Newman Specific rights apply.
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                      A service of: ASD at NASA / GSFC
                             & Michigan Tech. U.

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