Diamond believes that the population density of the Classic Mayan civilization reached 1,500 persons per square mile. That’s double the current density, for example, of Rwanda and Burundi, two of the most crowded and troubled nations in Africa. Warfare over scarce resources inevitably broke out, leading to a complete societal collapse—a peak population of between 5 million and 14 million in 800 CE tumbled 80 or 90 percent in less than a century.
“We have to wonder why the kings and nobles failed to recognize and solve these seemingly obvious problems undermining their society. Their attention was evidently focused on their short-term concerns of enriching themselves, waging wars, erecting monuments, competing with each other, and extracting enough food from the peasants to support these activities. Like most leaders throughout human history, the Maya kings and nobles did not heed long-term problems, insofar as they perceived them,” writes Diamond.
The Mayan fall in power, prosperity, and population is quite possibly the most drastic any civilization has ever experienced. Does this invalidate their wisdom? It certainly doesn’t recommend it, except possibly in the area of catastrophe, which historically they know better than just about anyone else.
SPINNING LIKE A TOP
Righteous indignation was still pumping my brain when it dawned on me that the exchange between those two computer nerds on top of the Tikal pyramid probably wasn’t far off in spirit from the conversations that took place there originally. That very pyramid, in fact, was built specifically for astronomers to chart the heavens and keep track of celestial time.
Imagine two ancient Mayan astronomers, an elder and a younger, arguing about the stars on the eve of the vernal equinox. The elder observes that Polaris, the pole star of the Northern Hemisphere, is not in the same position it was on the vernal equinox thirty-six years ago, when he first started his observations. Over that time, Polaris has shifted in a westward direction, the elder declares, about the same distance as the width of the full Moon (roughly half a degree).
The younger astronomer recoils from the heresy. From time immemorial, an article of celestial faith is that, on any given day and date, the stars are supposed to be in exactly the same position from one year to the next. To say otherwise would mean that the great heavenly clock is not keeping perfect time.
Eventually the truth won out, and the elder’s discovery was incorporated into the Mayan cosmology. Perhaps as long as two and a half millennia ago, their ancient astronomers sussed out the astonishing fact that slowly, inexorably, the heavens crank westward at the rate of about 1 degree every 72 years, and complete a full circle every 26,000 Mayan solar years, a period equal to five Suns. A stargazer who lived for the next 26,000 Mayan solar years would see the polestar change from Polaris, also known as the North Star, to Vega, and then back to Polaris, as would a stargazer who lived from 26,000 Mayan solar years until now.
As we’ve been reminded over and over again since Copernicus, it’s not the heavens but the Earth that moves. In fact the Earth spins like a top on its axis. Watch a top spin, and you will note that its axis slowly describes its own tiny circle. That process is called precession and is entirely analogous to what we perceive as the rotation of the heavens in the sky.
Precession seems to have been discovered more or less simultaneously by a variety of different cultures. Traditionally, credit for first understanding that the heavens are in fact a giant clock that takes eons to move around goes to Hipparchus, an ancient Greek astronomer who lived in the second century BCE. However, it now seems likely that the ancient Egyptians, Babylonians, and Sumerians had earlier grasped the concept.
Persian and Indian astronomers also knew of precession, perhaps via the ancient Greeks, and were so impressed with the fact that the heavens move ever so slowly in an incredibly huge circle that they attributed it all to a deity, Mithra. During the sixth century BCE, Mithraism spread rapidly throughout India, the Middle East, and Europe. At its peak in the second century CE, Mithraism was more widely embraced than Christianity throughout the Roman Empire. Its central doctrine sprang from the sacrifice of a sacred bull, from whose body all goodness sprang. Although Mithraism virtually vanished in the third century CE, with Islam eventually taking over in Persia later on, the Persian New Year is still celebrated on the vernal equinox, usually March 20, a festive holdover from Mithraic days.
Long-term cycles in the Earth’s orbit and spin have more than cosmetic importance, according to Milutin Milankovitch, the brilliant Serbian astronomer. He examined three cycles, now known as the Milankovitch cycles, for their potential impacts on climate and catastrophe on Earth. The first cycle, known as eccentricity, simply accounts for the fact that the shape of the Earth’s orbit around the Sun changes from being almost perfectly circular to slightly more elliptical, over a cycle that lasts from 90,000 to 100,000 years. Right now we are at the most circular stage in that cycle, meaning that there’s only about a 3 percent variation in distance, and a 6 percent variation in received solar energy, between perihelion, the point where our planet is closest to the Sun, and aphelion, the point where our planet is farthest from the Sun. However, as the Earth’s eccentricity cycle proceeds toward the point at which our orbit is most elliptical, the amount of solar radiation our planet receives at perihelion will be 20 to 30 percent greater than at aphelion. This will make for sharper seasonal contrasts and profound climate change. Milankovitch and his followers believe that previous ice ages are largely attributable to the Earth’s eccentricity cycle.
Currently, perihelion occurs during the second week of January, shortly after the Northern Hemisphere’s winter solstice. This works out nicely, at least for those of us in the northern half of the world, because we are getting that extra 6 percent boost of solar energy right in the dead of winter. This cozy situation won’t last forever, Milankovitch observed. As the north polestar shifts from Polaris to Vega, the orientation of the Earth toward the Sun also changes, to a situation where perihelion will come during the Northern Hemisphere’s summer solstice, meaning that we’ll be getting our energy boost right in the dead of summer. And by then, 13,000 years from now, that energy boost will be two or three times as powerful as the boost we get today, because the Earth’s orbit will have become more elliptical, making for greater differences between the amounts of solar radiation received at different points of the year. All in all, the Northern Hemisphere’s summers will be hotter, and the winters colder, making Southern Hemisphere real estate a good long-term buy.
WE ALL WERE TAUGHT that the Earth tilts on its axis, although just why the Earth’s axis tilts at all rather than going straight up and down is still open to conjecture. Some believe that eons ago the Earth was bonked by an asteroid or another planet, knocking us cockeyed; others argue that the pull of the Sun’s gravitational field, which would be strongest at the Earth’s equator, where most of our planet’s mass is, causes the Earth to tilt, “stomachward,” to the Sun.
The tilt of the Earth’s axis is what causes the seasons, since at different times of the year different parts of the planet lean either into or away from the sunlight. When the Northern Hemisphere is receiving direct sunlight, it is summer here, and days are longer than nights. At that time the Southern Hemisphere is receiving indirect sunlight, its winter, when nights are longer than days. On two days every year, the spring and fall equinoxes, all parts of the Earth have equal day and night.
In a cycle known as obliquity, Milankovitch discovered that, over the course of about 41,000 years, the tilt in the Earth’s axis changes from 22.1 degrees to 24.5 degrees. Currently the Earth’s tilt is 23.5 degrees. The greater the tilt, the more exaggerated the contrast between seasons. Imagine yourself on a cold winter night, standing over a campfire. Now lean your face closer to the fire. It gets hotter and your butt gets thrust farther out in the cold. This is just what happens to the Earth as its axial tilt becomes more pronounced.
Although some contemporary scientists quail at the notion, a preponderance of evidence from archaeological texts and artifacts clearly indicates that the ancients had a rudimentary grasp of astronomical cycles such as precession, eccentricity, and obliquity. This knowledge gave astronomer-priests an exalted position