                        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.

                                2021 July 17

                           Alphonsus and Arzachel
                   Image Credit & Copyright: Noel Donnard

   Explanation: Point your telescope at tonight's first quarter Moon.
   Along the terminator, the shadow line between night and day, you might
   find these two large craters staring back at you with an owlish gaze.
   Alphonsus (left) and Arzachel are ancient impact craters on the north
   eastern shores of Mare Nubium, the lunar Sea of Clouds. The larger
   Alphonsus is over 100 kilometers in diameter. A low sun angle
   highlights the crater's sharp 1.5 kilometer high central peak in bright
   sunlight and dark shadow. Scouting for potential Apollo moon landing
   sites, the Ranger 9 spacecraft returned closeup photographs of
   Alphonsus before it crashed in the crater just northeast (left) of its
   central mountain in 1965. Alpetragius, between Alphonsus and Arzachel,
   is the small crater with the deeply shadowed floor and overly large
   central peak.

              Tomorrow's picture: 2.5 million light-years away
     __________________________________________________________________

       Authors & editors: Robert Nemiroff (MTU) & Jerry Bonnell (UMCP)
            NASA Official: Phillip Newman Specific rights apply.
                NASA Web Privacy Policy and Important Notices
                      A service of: ASD at NASA / GSFC
                             & Michigan Tech. U.


