@Taw
Regarding the seemingly never ending shock and surprise at the precision in astronomy that the ancients were able to exercise.
We have evidence of very precise and exacting astronomical feats performed by the Chinese, the Sumerians/Babylonians, Egyptians, Maya and Inca and I am sure countless more that we haven't thought much about. Even the Anasazi peoples of the American Southwest have exhibited tremendous skill in astronomical tracking and marking.
My point: AND WHY SHOULDN'T THEY?
The ability to mark time, predictably and to be able to travel from place to place, whether on land or at sea was just as important to the ancients, if not more so than ever for modern man. It does not surprise me one bit that ancient cultures, many of which lasted for a millenia, would exert a lot of resource and time to trying to get things right or as right as possible.
The precision of the Mayan calendar should not be thought to be so out of the reach of Man that it HAD to be "given" to us by aliens ... because we are too stupid otherwise, yadda yadda yadda.
What I find objectionable about these "aliens helped us" fans is that they are really saying that the human race is too inept to do things on it own. That's poppycock.