大象传媒

Kate Humble goes to Chichen Itza, Mexico, to join in the celebration of the spring equinox on 20 March. The ancient monument shows that the Mayans understood the way the Sun and Earth aligned twice every year.

Helen Czerski, a young physicist from Southampton University, shows that this alignment is due to Earth's tilt. On a beach in St Ives she demonstrates that the planet is always tilted at just over 23 degrees. Graphics of Earth鈥檚 orbit around the Sun then show how why this tilt creates the seasons.