The astronomers of TeotihuacÃ¡n were looking for the point on the landscape where the Sun "turned around" -- where it stood directly overhead at noon on the summer solstice. They found it in central Mexico. They built a ceremonial center there, and operated it for more than four centuries.
The site is known as Alta Vista. It was built before the year 500, and operated until around 900.
Alta Vista consisted of an elaborate temple complex. It was aligned with the cardinal directions, and with the sunrise on the equinoxes. At the equinoxes, as seen from one of the temple rooms, the Sun rose directly over the peak of a nearby mountain.
One room was built to watch for the summer solstice. It's known as the Hall of Columns, because it's filled with stone pillars. At precisely noon on the solstice, the Sun shone straight down on the pillars, so they cast no shadows -- an indication that the Sun had reached its northernmost point in the sky.
The astronomers also pecked two concentric rings and a central cross into the top of a mountain a few miles to the south -- a common Sun symbol in Mesoamerica. As seen from this site at the solstice, the Sun rose directly above the same mountain that was used as an equinox marker.
The solstice arrives tonight, marking the start of summer. So from Alta Vista, the Sun will rise above the mountain tomorrow morning, and stand high overhead at noon -- as it prepares to "turn around" and head southward once again.
Script by Damond Benningfield, Copyright 2009
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