Thursday, March 20, was the vernal equinox, the day when the day and night are equal in length, and the first day of spring. Angkor Wat was built in the 1100s, long before modern developments of science, but it was constructed so that the sun on the vernal equinox rises directly above the main tower of Angkor Wat. This is a stunning achievement with the limited knowledge of astronomy and cosmology and architecture available at that time, and a dramatic expression of the curiosity and creativity and intelligence of the human species. This year more than 85,000 visitors were at Angkor Wat to observe this phenomenon.