What is an equinox, and why does it happen?
The sun rises over the central stupa of Angkor Wat temple in Siem Reap. During the equinox, the sun's path skyward takes it directly over the middle spire of the temple.
The El Castillo pyramid in Chichen Itza, Mexico, is backlit by the setting sun. For a week before and after the spring and fall equinoxes, the dwindling sunlight creates a shadowy snake-like effect on the steps of the pyramid that attracts thousands.
In the Basilica San Petronio in Bologna, Italy, astronomer Egnazio Danti in 1575 constructed a so-called meridian line in the church. A hole in the roof allowed the sun to shine on the floor, and Danti tracked and analyzed the sun's movements, including during the equinoxes.
Most of the structures at Hovenweep Castle in southeastern Utah's Hovenweep National Monument were built by the Anasazi between A.D. 1200 and 1300 and were home to more than 2,500 people. The castle contains a room that archaeologists theorize was used as a solar calendar.
At Mnajdra Temple in Malta, the sun shines down a central corridor during the vernal equinox and illuminates the very heart of the structure.
