El Castillo, Temple of Kukulkan, a prominent Mesoamerican step-pyramid at the center of the Chichen Itza archaeological site in Mexico's Yucatán state. | Richard LeBel

The shadow of the serpent on the Pyramid of Kukulkán at Chichén Itzá is a famous astronomical and ritual phenomenon tied to the Maya calendar. On the spring and autumn equinoxes, sunlight strikes the pyramid’s northwest staircase in such a way that a series of triangular shadows appear along the balustrade, creating the illusion of a serpent’s body slithering downward. These shadows align with the large stone serpent head carved at the base of the stairs, making it seem as if the feathered serpe