The Zenith Sun A common characteristic in Mesoamerica is the observance of the sun's zenith passage. This happens when the sun passes directly overhead at noon. It appears twice a year around late April and mid-August. Many ancient sites from Mexico east to the Yucatan seem to have systems built into their architecture to show this phenomenon. In the Mayan city of Kabah there is a cylindrical stone marker placed vertically in a plaza that seems to act as a gnomon that will produce a shadow every day except during the time of the sun's zenith position when the shadow disappears. In Monte Alban, Oaxaca and Xochicalco, Mexico the devices are more sophisticated. These have Zenith tubes in buildings that direct the rays of the sun down their passages to produce a circle of light onto the floor of a darkened chamber. Looking up through the zenith tube Sun light on the floor of Xochicalco zenith tube. The Mixtec A-O glyph The Mixtec A-O glyph was their symbol for 'year'. The...
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