* Astronomy

The Aztec calendar stone, Mexica sun stone, Stone of the Sun (Spanish: Piedra del Sol), or Stone of the Five Eras, is a large monolithic sculpture that was excavated in the Zócalo, Mexico City's main square, on December 17, 1790. It was discovered whilst Mexico City Cathedral was being repaired. The stone is around 12 foot across and weighs about 24 tons.
The exact purpose and meaning of the stone is unclear. However archaeologists and historians have proposed a number of theories and it seems likely that there are many aspects to the stone.
One aspect of the stone is its religious significance. One theory is that the face at the centre of the stone represents Tonatiuh, the Mexica god of the sun. It is for this reason that the stone became known as the "sun stone". Richard Townsend proposed a different theory, claiming that the figure at the centre of the stone actually represents Tlaltecuhtli, the Mexica sea or earth monster who features in Mexica creation myths.
Another aspect of the stone relates to time, hense the name "calendar stone". Some of the circles of glyphs are the glyphs for the days of the month. Further, some of the symbols may represent the five ages that the Mexica believed the earth had passed through.
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