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. 2025 December 21 Your browser does not support the video tag. Solstice on a Spinning Earth Image Credit: [2]Meteosat 9, [3]NASA, [4]Earth Observatory, [5]Robert Simmon Explanation: Can you tell that today is a solstice by the tilt of the Earth? Yes. At a solstice, the [6]Earth's terminator -- the dividing line between night and day -- is tilted the most. The [7]featured time-lapse video demonstrates this by displaying an entire year on [8]planet Earth in twelve seconds. From [9]geosynchronous orbit, the [10]Meteosat 9 satellite recorded [11]infrared images of the Earth every day at the same [12]local time. The video started at the [13]September 2010 equinox with the terminator line being vertical: an equinox. As the [14]Earth revolved around the Sun, the terminator was seen to tilt in a way that provides less daily sunlight to the northern hemisphere, [15]causing winter in the north. At the [16]most tilt, winter solstice occurred [17]in the north, and summer [18]solstice in the south. 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 the billions of trips the Earth has taken -- and will take -- around the Sun. APOD Review: [23]RJN's Night Sky Network Lecture Tomorrow's picture: strange lightning __________________________________________________________________ [24]< | [25]Archive | [26]Submissions | [27]Index | [28]Search | [29]Calendar | [30]RSS | [31]Education | [32]About APOD | [33]Discuss | [34]> __________________________________________________________________ Authors & editors: [35]Robert Nemiroff ([36]MTU) & [37]Jerry Bonnell ([38]UMCP) NASA Official: Amber Straughn [39]Specific rights apply. [40]NASA Web Privacy, [41]Accessibility, [42]Notices; A service of: [43]ASD at [44]NASA / [45]GSFC, [46]NASA Science Activation & [47]Michigan Tech. U. References 1. https://apod.nasa.gov/apod/archivepix.html 2. https://www.eumetsat.int/our-satellites/meteosat-series 3. https://www.nasa.gov/ 4. https://earthobservatory.nasa.gov/ 5. https://www.nasa.gov/centers/goddard/about/people/RSimmon.html 6. https://en.wikipedia.org/wiki/Terminator_(solar) 7. https://www.youtube.com/watch?v=LUW51lvIFjg 8. https://spaceplace.nasa.gov/all-about-earth/ 9. https://en.wikipedia.org/wiki/Geosynchronous_orbit 10. https://en.wikipedia.org/wiki/Meteosat 11. https://science.nasa.gov/ems/07_infraredwaves/ 12. http://time.gov/ 13. http://apod.nasa.gov/apod/calendar/ca1009.html 14. https://science.nasa.gov/earth/ 15. https://spaceplace.nasa.gov/seasons/ 16. https://www.reddit.com/media?url=https://external-preview.redd.it/21AJtS8T1bwvpyZPzjD9iOMijuFVaovzIVlNB2EZPJg.jpg?auto=webp&s=7f69f67d6aa77074bcd4e33ebaa47d79dc152b1e 17. https://science.nasa.gov/kids/earth/which-pole-is-colder/ 18. https://en.wikipedia.org/wiki/Solstice 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/ap220321.html 23. https://www.youtube.com/watch?v=_txUmGTtBhQ 24. https://apod.nasa.gov/apod/ap251220.html 25. https://apod.nasa.gov/apod/archivepix.html 26. https://apod.nasa.gov/apod/lib/apsubmit2015.html 27. https://apod.nasa.gov/apod/lib/aptree.html 28. https://antwrp.gsfc.nasa.gov/cgi-bin/apod/apod_search 29. https://apod.nasa.gov/apod/calendar/allyears.html 30. https://apod.com/feed.rss 31. https://apod.nasa.gov/apod/lib/edlinks.html 32. https://apod.nasa.gov/apod/lib/about_apod.html 33. https://asterisk.apod.com/discuss_apod.php?date=251221 34. https://apod.nasa.gov/apod/ap251222.html 35. http://www.phy.mtu.edu/faculty/Nemiroff.html 36. http://www.phy.mtu.edu/ 37. https://antwrp.gsfc.nasa.gov/htmltest/jbonnell/www/bonnell.html 38. http://www.astro.umd.edu/ 39. https://apod.nasa.gov/apod/lib/about_apod.html#srapply 40. https://www.nasa.gov/about/highlights/HP_Privacy.html 41. https://www.nasa.gov/general/accessibility/ 42. https://www.nasa.gov/privacy/ 43. https://astrophysics.gsfc.nasa.gov/ 44. https://www.nasa.gov/ 45. https://www.nasa.gov/centers/goddard/ 46. https://science.nasa.gov/learners 47. http://www.mtu.edu/