The Descent of Kukulkan.
As in every equinox, when the sun is above the equator and the day lasts the same as the night, the shadow of the feathered snake appears on the setting alpharda of the north staircase, shortly before sunset. It is made up of seven inverted triangles of light that appear to descend and join at the base of the staircase with the stone head of the Kukulkan serpent.













