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 November 30

                        Star Trails for a Red Planet
                   Image Credit & Copyright: Dengyi Huang

   Explanation: Does Mars have a north star? In long exposures of Earth's
   night sky, star trails make concentric arcs around the north celestial
   pole, the direction of our fair planet's axis of rotation. Bright star
   Polaris is presently the Earth's North Star, close on the sky to
   Earth's north celestial pole. But long exposures on Mars show star
   trails too, concentric arcs about a celestial pole determined by Mars'
   axis of rotation. Tilted like planet Earth's, the martian axis of
   rotation points in a different direction in space though. It points to
   a place on the sky between stars in Cygnus and Cepheus with no bright
   star comparable to Earth's north star Polaris nearby. So even though
   this ruddy, weathered landscape is remarkably reminiscent of terrain in
   images from the martian surface, the view must be from planet Earth,
   with north star Polaris near the center of concentric star trails. The
   landforms in the foreground are found in Qinghai Province in
   northwestern China.

                     Tomorrow's picture: blue starburst
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       Authors & editors: Robert Nemiroff (MTU) & Jerry Bonnell (UMCP)
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