In this composite image, the sun has reached its northernmost point in Earth's sky, marking a season change and the first solstice of the year 2004. NASA/ESA hide caption

toggle caption NASA/ESA

Do You Really Know Why Earth Has A Solstice?

  • Download
  • <iframe src="https://www.npr.org/player/embed/460655319/460657813" width="100%" height="290" frameborder="0" scrolling="no" title="NPR embedded audio player">

A replica Mayan Calendar Round showing the date September 21, 2004, opening day for the Smithsonian's National Museum of the American Indian. Molly Stephey/Smithsonian's National Museum of the American Indian hide caption

toggle caption Molly Stephey/Smithsonian's National Museum of the American Indian