The Mayans and their calendars are getting a bit of a bad rap today, undeservedly. They were skilled astronomers and mathematicians who produced remarkably precise astronomical tables.

The ancient Maya didn't just observe the night sky, they recorded the movements of Sun, Moon and planets. Those records were used to calculate the cycles of the sun, moon and planets and ultimately create calendars. Those calculations were very good, better than what would be calculated in Europe and the Middle East many years later.

The time required for the Sun to return to the same point in the sky, a solar year, was used in calculations of the seasons as well as dates of religious significance. Modern science defines that solar year as 365 days, 5 hours, 48 minutes, 27 seconds. The Mayan calculation was
23 seconds off from the modern one. This level of accuracy is even more amazing when you consider that it was done hundreds of years before the invention of the telescope with observatories made of stone.

A few hundred years later, Egyptian mathematician and astronomer Claudius Ptolemy published a solar year calculation in his "Handy Tables" publication. These calculations were based on his own as well as 800 years worth of records from other astronomers. Ptolemy was nearly 7 hours off.

The movement of Venus through the sky was of particular interest to Maya rulers who used its appearance to plan coronations and for when to wage war. Mayan astronomers calculated the over 583 days it takes for Venus to return to the same point in the sky to an accuracy of within
15 minutes. This also suggests that what we know of Mayan astronomy is based on hundreds of years of observations.

You can see Venus in the eastern pre-dawn sky this month. It will appear as a bright star just off the horizon. Saturn appears as a less-bright dot above.

Tony Rice is a volunteer in the NASA/JPL Solar System Ambassador program and software engineer at Cisco Systems. You can follow him on twitter @rtphokie.