This is the autumn equinox, September 21-22, an important day in the ancient culture of Yucatán. People still take note of the traditions, and they become important times for tourists to visit the area.
Just thinking about archaeological sites such as this, only about an hour's drive from Mérida makes my wishbone grow.
If you would like to visit us here, consider this tidbit from a travel site:
El Castillo at Chichen-Itza, Yucatán
For a thousand years, the slanting rays of the setting sun have played a spectacular
shadow and light game with this great Mayan pyramid. During the [vernal (March 20 or 21) and autumnal (September 21 or 22)]equinoxes, at the appointed hour, the shadow of the Feathered Serpent, Kukulcan appears on the [northern stairway] leading to the top of the Castillo. ...and vanishes.
Did you know that Kukulcan is the Mayan name for the Feathered Serpent God (also known as Quetzalcoatl to the Aztecs)?
http://www.world-mysteries.com/chichenitza_sn.htm