MSGID: 1:153/757.0 7d30b58b   
   TZUTC: -0700   
   CHRS: LATIN-1 2   
                           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.   
      
                                   2022 March 21   
      
                                  The Sky in 2021   
       Image Credit & Copyright: Cees Bassa (Netherlands Institute for Radio   
                                    Astronomy)   
      
      Explanation: What if you could see the entire sky -- all at once -- for   
      an entire year? That, very nearly, is what is pictured here. Every 15   
      minutes during 2021, an all-sky camera took an image of the sky over   
      the Netherlands. Central columns from these images were then aligned   
      and combined to create the featured keogram, with January at the top,   
      December at the bottom, and the middle of the night running vertically   
      just left of center. What do we see? Most obviously, the daytime sky is   
      mostly blue, while the nighttime sky is mostly black. The twelve light   
      bands crossing the night sky are caused by the glow of the Moon. The   
      thinnest part of the black hourglass shape occurs during the summer   
      solstice when days are the longest, while the thickest part occurs at   
      the winter solstice. Yesterday was an equinox -- when night and day   
      were equal -- and the northern-spring equinox from one year ago can   
      actually be located in the keogram -- about three-quarters of the way   
      up.   
      
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                     Tomorrow's picture: a whale of an aurora   
        __________________________________________________________________   
      
          Authors & editors: Robert Nemiroff (MTU) & Jerry Bonnell (UMCP)   
               NASA Official: Phillip Newman Specific rights apply.   
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                         A service of: ASD at NASA / GSFC   
                                & Michigan Tech. U.   
      
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