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 December 29

               Cassini Spacecraft Crosses Saturn's Ring Plane
    Image Credit: NASA, ESA, JPL, ISS, Cassini Imaging Team; Processing:
                           Fernando Garcia Navarro

   Explanation: If this is Saturn, where are the rings? When Saturn's
   "appendages" disappeared in 1612, Galileo did not understand why. Later
   that century, it became understood that Saturn's unusual protrusions
   were rings and that when the Earth crosses the ring plane, the edge-on
   rings will appear to disappear. This is because Saturn's rings are
   confined to a plane many times thinner, in proportion, than a razor
   blade. In modern times, the robot Cassini spacecraft orbiting Saturn
   frequently crossed Saturn's ring plane during its mission to Saturn,
   from 2004 to 2017. A series of plane crossing images from 2005 February
   was dug out of the vast online Cassini raw image archive by interested
   Spanish amateur Fernando Garcia Navarro. Pictured here, digitally
   cropped and set in representative colors, is the striking result.
   Saturn's thin ring plane appears in blue, bands and clouds in Saturn's
   upper atmosphere appear in gold. Details of Saturn's rings can be seen
   in the high dark shadows across the top of this image, taken back in
   2005. The moons Dione and Enceladus appear as bumps in the rings.

   Free Presentation: APOD Editor to show best astronomy images of 2019 --
                    and the decade -- in NYC on January 3
                   Tomorrow's picture: nebulae triple play
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       Authors & editors: Robert Nemiroff (MTU) & Jerry Bonnell (UMCP)
            NASA Official: Phillip Newman Specific rights apply.
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                             & Michigan Tech. U.

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