Equinox in Chichen-Itza 20-03-2013

The astronomical Spring Equinox this year fell on the 20th March.
Every year at Chichen-Itza on the spring and winter equinox we can witness the incredible accuracy of the Maya architecture integrated with their well known astronomical knowledge.
The equinox is the day of the year when night and day are about equal length and when the sun rises precisely from East and sets exactly in the West.
It is incredible how the Maya aligned the "Castillo" pyramid and designed it in such a way that, only around the equinoxes for a period of a few days, we can observe a special shadow and light effect resembling a descending snake on the north side of the building.
During the equinox the sun casts its rays on the pyramid, forming seven isosceles triangles that resemble the body of a serpent descending the pyramid and joining the huge serpent's head sculpture at the base of the stairway.
     The first triangles of light projection are visible starting from 4pm and culminate in the complete zigzag shadow pattern just a few minutes before 5pm.