On Mon, 5 Jan 2015 07:48:20 -0800 (PST), Tim
wrote:

Gerald, it's all amazing isn't it?

===

It certainly is. Two years ago we visited the Mayan pyramids in
Chichén Itzá, Mexico. It turns out that the ancient Mayans were also
keen observers of celestial phenomena and had an onsite observatory
dedicated to those observations. They were aware of planetary
motions and relative orbits around the sun, including the fact that
Mars and Mercury were farther from the sun than Earth, and that Venus
and Mercury were closer. They also had a very accurate calendar
which took leap years into account. All of that was more than a
thousand years ago.