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.

                              2021 September 22

         IFRAME: [2]https://www.youtube.com/embed/LUW51lvIFjg?rel=0

                         Equinox on a Spinning Earth
    Image Credit: [3]Meteosat 9, [4]NASA, [5]earthobservatory, [6]Robert
                                   Simmon

   Explanation: When does the line between night and day become vertical?
   Today. Today is an [7]equinox on planet Earth, a time of year when day
   and night are most nearly equal. At an equinox, the [8]Earth's
   terminator -- the dividing line between day and night -- becomes
   vertical and connects the [9]north and [10]south poles. The
   [11]featured time-lapse video demonstrates this by displaying an entire
   year on planet Earth in twelve seconds. From [12]geosynchronous orbit,
   the [13]Meteosat 9 satellite recorded [14]these infrared images of the
   Earth every day at the same [15]local time. The video started at the
   [16]September 2010 equinox with the terminator line being vertical. As
   the [17]Earth revolved around the Sun, the terminator was seen to tilt
   in a way that provides less daily sunlight to the northern hemisphere,
   [18]causing winter in the north. As the year progressed, the [19]March
   2011 equinox arrived halfway through the video, followed by the
   terminator [20]tilting the other way, [21]causing winter in the
   southern hemisphere -- and summer in the north. The captured year ends
   again with the [22]September equinox, concluding another of billions of
   trips the Earth has taken -- and will take -- around the Sun.

                   Tomorrow's picture: 22 minute moonrise
     __________________________________________________________________

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     __________________________________________________________________

    Authors & editors: [34]Robert Nemiroff ([35]MTU) & [36]Jerry Bonnell
                                 ([37]UMCP)
          NASA Official: Phillip Newman [38]Specific rights apply.
              [39]NASA Web Privacy Policy and Important Notices
                A service of: [40]ASD at [41]NASA / [42]GSFC
                           & [43]Michigan Tech. U.

References

   1. https://apod.nasa.gov/apod/archivepix.html
   2. https://www.youtube.com/embed/LUW51lvIFjg?rel=0
   3. https://www.eumetsat.int/our-satellites/meteosat-series
   4. https://www.nasa.gov/
   5. https://earthobservatory.nasa.gov/
   6. https://www.nasa.gov/centers/goddard/about/people/RSimmon.html
   7. https://en.wikipedia.org/wiki/Equinox
   8. https://en.wikipedia.org/wiki/Terminator_(solar)
   9. https://climatekids.nasa.gov/polar-temperatures/
  10. https://apod.nasa.gov/apod/ap131211.html
  11. https://www.youtube.com/watch?v=LUW51lvIFjg
  12. https://www.nasa.gov/audience/forstudents/postsecondary/features/geo_feature_prt.htm
  13. https://en.wikipedia.org/wiki/Meteosat
  14. https://earthobservatory.nasa.gov/IOTD/view.php?id=52248
  15. http://time.gov/
  16. http://apod.nasa.gov/apod/calendar/ca1009.html
  17. https://solarsystem.nasa.gov/planets/earth/overview/
  18. https://spaceplace.nasa.gov/seasons/en/
  19. http://apod.nasa.gov/apod/calendar/ca1103.html
  20. https://media3.giphy.com/media/JOe1P4jUAhTKhPI787/giphy.gif
  21. http://www.universetoday.com/75843/why-are-there-seasons/
  22. https://apod.nasa.gov/apod/ap190923.html
  23. https://apod.nasa.gov/apod/ap210921.html
  24. https://apod.nasa.gov/apod/archivepix.html
  25. https://apod.nasa.gov/apod/lib/apsubmit2015.html
  26. https://apod.nasa.gov/apod/lib/aptree.html
  27. https://antwrp.gsfc.nasa.gov/cgi-bin/apod/apod_search
  28. https://apod.nasa.gov/apod/calendar/allyears.html
  29. https://apod.nasa.gov/apod.rss
  30. https://apod.nasa.gov/apod/lib/edlinks.html
  31. https://apod.nasa.gov/apod/lib/about_apod.html
  32. http://asterisk.apod.com/discuss_apod.php?date=210922
  33. https://apod.nasa.gov/apod/ap210923.html
  34. http://www.phy.mtu.edu/faculty/Nemiroff.html
  35. http://www.phy.mtu.edu/
  36. https://antwrp.gsfc.nasa.gov/htmltest/jbonnell/www/bonnell.html
  37. http://www.astro.umd.edu/
  38. https://apod.nasa.gov/apod/lib/about_apod.html#srapply
  39. https://www.nasa.gov/about/highlights/HP_Privacy.html
  40. https://astrophysics.gsfc.nasa.gov/
  41. https://www.nasa.gov/
  42. https://www.nasa.gov/centers/goddard/
  43. http://www.mtu.edu/