Tens of thousands of people all over the world are finalizing their travel plans and getting ready to travel to Chichen-Itzá in order to be there on the spring equinox. They'll watch a magnificent light and shadow spectacle on the side of the north-facing stairway of the Castillo, a temple most probably dedicated to Kukulcan, the Maya version of Quetzalcoatl.
The sun, on its apparent trip north, will pass over the equator in the early morning hours of March 20. That evening, as it sets over the Yucatan Peninsula, the north-westernmost corner of the stepped pyramid will cast shadows on the outside of the 'banister' of one of the four stairways leading to the top of the pyramid. A series of illuminated triangles will be projected on the side of the stairway. The serpent's head at the base of the stairway will be fully illuminated -- the triangles will become the serpent's body.
If you're going, I'd suggest you do so two days before or after the equinox. The effect will be similar and you'll be able to witness it without the crowds and masters of ceremonies sent out by the tourism department with loudspeakers to 'improve' on what the sun and ancient Maya astronomers joined forces in creating.
Take a small scissor legged folding chair or a beach towel to lie on and be comfortable. It takes a while for the whole event to play out. If you're not comfortable it might seem like Mr. Sun has gotten stuck in the sky.
Only two of the Castillo's four stairways have been restored. Fortunately one of them hosts the light and shadow event. As is characteristic of prominent post-classic temples, it sits right in the middle of a huge plaza. When Chichen-Itza flourished it had a large population and certainly attracted large numbers of people on the equinoxes. They most probably watched and experienced the event in awe and silence.
As the light and shadow event plays out on the Castillo there will be another light and shadow event at Chichen-Itza, at the very same time, which probably won't be witnessed by anyone. However it will occur -- even if no one is there to see it -- in a very small space in the uppermost room of the Caracol, which probably functioned as an astronomical observatory.
Three surviving windows face into an observation chamber at the top of what was a round tower but now looks more like an upended conch shell. The windows are square (about 50x50 cm.) with very long windowsills (about two meters). Long windowsills restrict the view -- nevertheless a considerable expanse of horizon can be seen. One vernal equinox, while the crowd was watching the light show on the Castillo, I was the only one in the observatory chamber of the Caracol. The setting sun created a shadow on half the windowsill leaving the other half illuminated. A diagonal line separated light from shadow -- a line from the right hand corner on the inside, to the left hand corner on the outside of the windowsill. Perfectly straight -- a precise line of sight. Marvelous. Each windowsill provides two horizontal lines of sight. Different nights offer different events to be seen. Modern astronomers have identified twenty astronomical events that can be seen through the Caracol's surviving windows.
Last week I described Xochicalco's observatory which allows for focused views of heavenly objects -- something the Caracol observatory cannot do since it is set up for naked eye observations along designated sightlines. Xochicalco's observatory restricts viewing to one spot in the sky while the Caracol tower offered a full circle of views of the horizon through its multiple windows. In a simlar vein, though Xochicalco has only one observation shaft, I suspect that doorways -- now filled with rubble -- opening off the tunnel leading to the observation chamber accessed other observation rooms where shafts point to different spots in the sky.
Xochicalco's astronomers could not move their focused telescopes. But, could they move themselves to another room -- for a different view into the sky -- just as astronomers in the Caracol could move to another window? Xocicalco's observatory, the Caracol's observation windows, and the light and shadow spectacle on the Castillo are very different yet each served ancient astronomer-priests in verifying that their calendar was synchronized with the council of the gods. That, in turn, confirmed that their offerings were being delivered to their gods at the appropriate moments in time.
Of the three, the Castillo required the greatest coordination of architects and astronomer-priests in its design. Unlike Xochicalco's observatory and the Caracol's windows, the Castillo offered a public event for the whole population. It is still fulfilling that function today.