… is astronomy, as the New York Times notes in explaining the equinox:
Archaeological evidence abounds that astronomy is among the oldest of professions, and that people attended with particular zeal to the equinoxes and the solstices. The Great Sphinx of Egypt, for example, built some 4,500 years ago, is positioned to face toward the rising sun on the vernal equinox.
In the 1,500-year-old Mayan city of Chichén Itzá, in Mexico’s Yucatán peninsula, the magnificent Kukulcán Pyramid practically slithers to life each spring equinox evening, as the waning sun casts a shadow along its steps of seven perfectly symmetrical isosceles triangles, a pattern suggesting the diamondback skin of a snake.
Of course, this is really because the space aliens who built the pyramids had GPS (Galactic Positioning System) receivers, and… Whoops. I’ve said too much.