[JBW1949]

OK...Thanks...The story says it was the solstice...I told y’all my memory is fading fast...:o))

[disndat]

I think I was reading that it happened on the equinoxes in another article. Looking.

[disndat]

The phenomenon that El Castillo is famous for occurs twice each year, at the spring and fall equinoxes. (In fact, the effect is viewable for a week before and after each equinox.) As the equinox sun sets, a play of light and shadow creates the appearance of a snake that gradually undulates down the stairway of the pyramid. This diamond-backed snake is composed of seven or so triangular shadows, cast by the stepped terraces of the pyramid. The sinking sun seems to give life to the sinuous shadows, which make a decidedly snaky pattern on their way down the stairs.