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 August 12

                     The Shifting Tails of Comet NEOWISE
                  Image Credit & Copyright: Ignacio Llorens

   Explanation: Keep your eye on the ion tail of Comet NEOWISE. A tale of
   this tail is the trail of the Earth. As with all comets, the blue ion
   tail always points away from the Sun. But as Comet C/2020 F3 (NEOWISE)
   rounded our Sun, its ion tail pointed in slightly different directions.
   This is because between 2020 July 17 and July 25 when the featured
   images were taken, the Earth moved noticeably in its orbit around the
   Sun. But the Earth's motion made the Sun appear to shift in the sky. So
   even though you can't see the Sun directly in the featured image(s),
   the directions of the ion tails reveal this apparent solar shift. The
   Sun's apparent motion is in the ecliptic, the common plane where all
   planets orbit. The featured five image composite was meticulously
   composed to accurately place each comet image -- and the five
   extrapolated solar positions -- on a single foreground image of Turó de
   l'Home Mountain, north of Barcelona, Spain Comet NEOWISE is no longer
   the impressive naked-eye object it was last month, but it can still be
   found with a small telescope as it heads back to the outer Solar
   System.

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       Authors & editors: Robert Nemiroff (MTU) & Jerry Bonnell (UMCP)
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