The Mayans were consummated astronomers. This calendar sculpture shows the Maya God of Time at the center, supporting the burden of time on his back. He is surrounded by the hieroglyphs of the 19 months. The calendar is based in the cycles of earth with 18 months of 20 days. The 19th month uses 5 extra nameless days, considered evil or bad luck days.
All in all this totaled 365 days. 
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