                        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.

                                2020 July 22

                    The Structured Tails of Comet NEOWISE
          Image Credit & Copyright: Zixuan Lin (Beijing Normal U.)

   Explanation: What is creating the structure in Comet NEOWISE's tails?
   Of the two tails evident, the blue ion tail on the left points directly
   away from the Sun and is pushed out by the flowing and charged solar
   wind. Structure in the ion tail comes from different rates of expelled
   blue-glowing ions from the comet's nucleus, as well as the always
   complex and continually changing structure of our Sun's wind. Most
   unusual for Comet C/2020 F3 (NEOWISE), though, is the wavy structure of
   its dust tail. This dust tail is pushed out by sunlight, but curves as
   heavier dust particles are better able to resist this light pressure
   and continue along a solar orbit. Comet NEOWISE's impressive dust-tail
   striations are not fully understood, as yet, but likely related to
   rotating streams of sun-reflecting grit liberated by ice melting on its
   5-kilometer wide nucleus. The featured 40-image conglomerate, digitally
   enhanced, was captured three days ago through the dark skies of the
   Gobi Desert in Inner Mongolia, China. Comet NEOWISE will make it
   closest pass to the Earth tomorrow as it moves out from the Sun. The
   comet, already fading but still visible to the unaided eye, should fade
   more rapidly as it recedes from the Earth.

   Notable NEOWISE Images Submitted to APOD: July 21 || 20 || 19 || 18 ||
          17 || 16 || 15 || 14 || 13 || 12 || 11 || 10 & earlier ||
                       Tomorrow's picture: open space
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       Authors & editors: Robert Nemiroff (MTU) & Jerry Bonnell (UMCP)
            NASA Official: Phillip Newman Specific rights apply.
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