Astronomy Picture of the Day

   [1]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
     [2]An image of the sky over the Netherlands taken every 15 minutes
    during 2021. Visible are night, day, solstices, equinoxes, moonglow,
    the blue hour, and more. Please see the explanation for more detailed
                                information.

                               The Sky in 2021
    Image Credit & Copyright: [3]Cees Bassa ([4]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 [5]all-sky camera took an image of the sky over
   the [6]Netherlands. Central [7]columns from these images were then
   aligned and combined to create the featured [8]keogram, with January at
   the top, December at the bottom, and the middle of the night running
   vertically just left of center. [9]What do we see? Most obviously, the
   daytime [10]sky is mostly blue, while the nighttime sky is mostly
   black. The twelve [11]light bands crossing the night sky are caused by
   the [12]glow of the Moon. The thinnest part of the black hourglass
   shape occurs during the summer [13]solstice when days are the longest,
   while the thickest part occurs at the winter [14]solstice. Yesterday
   was an [15]equinox -- when night and day were equal -- and the
   northern-spring [16]equinox from one year ago can actually be located
   in the keogram -- about three-quarters of the way up.

   Follow APOD on Instagram in: [17]English, [18]Indonesian, [19]Persian,
                       [20]Portuguese or [21]Taiwanese
                  Tomorrow's picture: a whale of an aurora
     __________________________________________________________________

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    Authors & editors: [33]Robert Nemiroff ([34]MTU) & [35]Jerry Bonnell
                                 ([36]UMCP)
          NASA Official: Phillip Newman [37]Specific rights apply.
              [38]NASA Web Privacy Policy and Important Notices
                A service of: [39]ASD at [40]NASA / [41]GSFC
                           & [42]Michigan Tech. U.

References

   1. https://apod.nasa.gov/apod/archivepix.html
   2. https://apod.nasa.gov/apod/image/2203/YearOfSky_Bassa_960.jpg
   3. https://twitter.com/cgbassa
   4. https://www.astron.nl/about/
   5. https://apod.nasa.gov/apod/ap011119.html
   6. https://en.wikipedia.org/wiki/Netherlands
   7. https://commons.wikimedia.org/wiki/File:Keogram_explainer.gif
   8. https://victoriaweather.ca/keogram.php#:~:text=What is a keogram
   9. https://i1.sndcdn.com/artworks-000064777927-e3ahj5-t500x500.jpg
  10. https://spaceplace.nasa.gov/blue-sky/en/
  11. https://apod.nasa.gov/apod/ap220301.html
  12. https://skyandtelescope.org/astronomy-news/how-bright-moon-exactly/
  13. https://scijinks.gov/solstice/
  14. https://blogs.nasa.gov/Watch_the_Skies/tag/solstice/
  15. https://blogs.nasa.gov/Watch_the_Skies/tag/equinox/
  16. https://apod.nasa.gov/apod/ap220320.html
  17. https://www.instagram.com/astronomypicturesdaily/
  18. https://www.instagram.com/apod.id/
  19. https://www.instagram.com/avastarapod/
  20. https://www.instagram.com/apodbrasil/
  21. https://www.instagram.com/apod_taigi/
  22. https://apod.nasa.gov/apod/ap220320.html
  23. https://apod.nasa.gov/apod/archivepix.html
  24. https://apod.nasa.gov/apod/lib/apsubmit2015.html
  25. https://apod.nasa.gov/apod/lib/aptree.html
  26. https://antwrp.gsfc.nasa.gov/cgi-bin/apod/apod_search
  27. https://apod.nasa.gov/apod/calendar/allyears.html
  28. https://apod.nasa.gov/apod.rss
  29. https://apod.nasa.gov/apod/lib/edlinks.html
  30. https://apod.nasa.gov/apod/lib/about_apod.html
  31. http://asterisk.apod.com/discuss_apod.php?date=220321
  32. https://apod.nasa.gov/apod/ap220322.html
  33. http://www.phy.mtu.edu/faculty/Nemiroff.html
  34. http://www.phy.mtu.edu/
  35. https://antwrp.gsfc.nasa.gov/htmltest/jbonnell/www/bonnell.html
  36. http://www.astro.umd.edu/
  37. https://apod.nasa.gov/apod/lib/about_apod.html#srapply
  38. https://www.nasa.gov/about/highlights/HP_Privacy.html
  39. https://astrophysics.gsfc.nasa.gov/
  40. https://www.nasa.gov/
  41. https://www.nasa.gov/centers/goddard/
  42. http://www.mtu.edu/