Mexican ruin was solar observatory.

The Danzantes temple at Monte Alban, one of the most popular tourist sites in Oaxaca, Mexico, is a 2,200-year-old solar observatory, claims University of Texas at Austin astrophysicist R. Robert Robbins. He says that the structure is like no other Indian observatory identified in the New World and apparently was constructed for mass viewing. "The point where you have to stand to make all the phenomena behave properly is at a gate in the plaza. At most solar temples, the vantage point is in a fairly inaccessible spot that could only have accommodated the astronomer-priest and a couple of other people at most. But at Monte Alban, a large number of people could be accommodated, so it's possible that the priest would bring big groups into the plaza to show them what was happening."

Constructed around 200 B.C., Monte Alban was excavated in the 1930s after centuries of neglect. Robbins discovered the astronomical significance of the temple when he traveled to Monte Alban soon after the autumnal equinox of 1989. Although archaeologists already had determined that one of the buildings on the grounds was of astronomical significance, no one had been able to figure out how the temple fit into the scheme of things.

Speculating that the temple was a solar observatory, Robbins arrived at the site about 11 days after the equinox and, with the aid of hand-held instruments, discovered a spot outside the plaza gate where the sun and physical markers atop the temple were aligned the evening the seasons changed. From the vantage point of the gate at sundown, the sun appears to descend into a narrow slot in the middle of the temple roof on the first day of fall and first day of spring - the two days the sun is directly on the celestial equator. By running some calculations, he determined that the sun descends into the south corner of the temple roof on the first day of winter (when the sun is at its...