Kukulkan is a mythical snake deity and has origins amoung the Maya of the Classic Period. El Castillo in Chichen Itza served as a temple to Kukulkan. During the spring and fall equinoxes the shadow cast by the angle of the sun and edges of the nine steps of the pyramid combined with the northern stairway and the stone serpent head carvings create the illusion of a massive serpent descending the pyramid.
Kukulkan's pyramid is essentially a nine-step structure culminating in a flat platform that supports a two-story temple. The height to the top platform is 24 metres, the temple adding another 6 metres. El Castillo's design is thought to relate to the Mayan calendar. Each of the four faces incorporates a broad, steep staircase consisting of 91 steps that ascends to the top platform. Counting the top platform as an additional step gives a total of 365 steps: 1 step for each day of the year. The staircases rise at an angle of 45 degrees to the horizontal, while the average inclination of the stepped pyramid itself is 53.3 degrees. The faces of the individual steps are sloped at a greater angle, approximately 73 degrees. The nine main platforms of the pyramid are thought to represent the 18 months of the haab, and the 52 panels represent the number of years it takes for a calendar round date to recur.
At the spring and fall equinoxes (March 21 and September 22) the sun projects an undulating pattern of light on the northern stairway for a few hours in the late afternoon-a pattern caused by the angle of the sun and the edge of the nine steps that define the pyramid's construction. These triangles of light link up with the massive stone carvings of snake heads at the base of the stairs, suggesting a massive serpent snaking down the structure. The moving snake on the Pyramid is an annual reminder over Chichen Itza, but this is an event which will only occur during a 72-year time window, from 1976 to 2048. Right at the centre of this time window is the year 2012, when the Great Cycle ends.