... 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.
Sort of off-topic, but this reminds me of a joke:
A doctor, an engineer and a lawyer are discussing the oldest profession on earth.
The doctor says: "Now look here, God had a rib removed from Adam in order to create Eve. This is a surgical procedure, so a doctor must have been present, and hence, we are the oldest profession on earth!"
The engineer replies: "Not so fast! If you look earlier in the bible, you will find how it describes the creation of order out of chaos. This is project management, structured work, and obviously an engineer must have been involved. We are the oldest profession on earth!"
The lawyer calmly asks: "Ah, gentlemen, who do you think created chaos...?"
Don't the effects of precession and nutation mean that the equinox / solstice sunrise/sunset are now at different azimuths than they were 1500-4000 y ago? Or is this already taken into account by the claims?
Ah, so astronomy is right up there with prostitution!