Advent Calendar of Science Stories 4: Solstice

The southeastern sky had been lightening for some time, stars slowly fading away. Off to the west, a band of clouds was moving in, obscuring stars as it came, but they wouldn't make it in time to block the sunrise. A good thing, as the last two dawns had been cloudy. There would be maybe two more chances this year to see if everything worked, then another full turn of the seasons before their next chance.

She sat on the cold ground, behind the offering bowls, a bit off the line of the main passage. She was inside the ring of posts marking the final perimeter, but outside what would become the vault, when those stones were finally hauled up the river and put in place. No vault yet, though; not for some years. But soon; this might be the last chance to shift the alignment of things.

The priests puttered around the stone bowls and their cargo of bones, but they were really just waiting for the sunrise, like everyone else. She thought back to ten years earlier, another cold winter dawn, when the hillside had been bare, and the chaos of junior priests scrambling to adjust the wooden posts defining the key alignment in the first crucial moments of dawn.

Now that path was flanked by two lines of huge stones, hauled great distances and heaved upright. At one end, the bowls; at the other, the heavy slabs that defined the entrance, one above the other, with the all-important space between them, at the height of a tall man's head.

An anticipatory murmur grew among the small crowd gathered on the hill watching the lightening sky, and the priests hastily organized themselves, and began chanting. Only a few moments later, the sun broke over the horizon, spreading yellow light across the rolling hills, the bend in the river below, the assembled people. And casting a dark shadows behind the great stones, stretching up and over the top of the hill, the bowls, and the chanting priests.

Except for one bright patch, a gap where light shone down the passage between the rows of stones, lighting up the ground directly between the bowls. To their credit, the priests didn't falter in the chant-- we knew that would happen-- but a chattering spread among the rest of the people on the hill, a mixture of excitement and relief. All their hard work hauling, lifting, and placing stones had come together.

There were many more years of work ahead, to be sure, hauling and placing the stones for the vault, covering the whole structure with more stone and earth. She likely wouldn't live to see its completion, but the critical part was done. The alignment was set, fixed by giant stones, and would mark the turning of the year for generations to come...<

One of the highlights of our brief trip to Ireland this summer was taking a tour of the famous passage tomb at Newgrange (shown above). This isn't quite as well known as Stonehenge, but it's around a thousand years older, and in some ways a more impressive achievement. It consists of a giant mound of stones and earth with a narrow 19-meter passage (a tight squeeze for a modern American-- I wasn't sure I'd make it through) running into a high vault in the center of the mound. On a handful of days around the winter solstice, light from the rising sun passes through a small opening above the entrance, down the long narrow passage, and illuminates the central chamber for a few minutes before it falls into darkness again.

The people who built Newgrange didn't have written language-- some of the stones are marked with pretty spiral patterns, but no other inscriptions remain-- so we don't know much about who they were, or exactly what they used the mound for. We do know one thing, though: they were scientists. The astronomical alignment of Newgrange is too perfect to be accidental, and was clearly the result of years of careful observation and planning. The precision of the construction is amazing, as well-- the central vault of overlapping stone slabs is completely watertight, and has remained dry for five thousand years. In Ireland.

I've mentioned before that I have an unaccountable fondness for the dippy pseudoscience of "Ancient Aliens" on the History network. When I teach about Newgrange in my course on the science of timekeeping (which I'll be doing again in January), I use a clip from the show that makes the usual absurd claims about the impossibility of ancient people doing this sort of thing (the bit I use isn't from this episode, but the "It looks like a UFO!" bit in the linked clip is pretty special, too...). They try to spin it as requiring a vast knowledge of astronomy, that only could've come from a more advanced civilization.

In reality, though, there's nothing especially high-tech involved here. In fact, as Neil deGrasse Tyson points out, all you need is a couple of sticks (I also assign this essay, before the class where I show the Ancient Aliens clip). It requires a good deal of patience, but if you pick a spot, and position vertical stick every day so its shadow falls on the spot you want, you can easily define the path you need to make your very own Newgrange-style solstice marker. Or any other day you might happen to want to celebrate-- there are other Neolithic passage tombs aligned with the equinoxes, or if you really wanted to, you could set one up to light up on the few days around your birthday.

(Getting the giant stones set up to make the passage and vault is no trivial matter, mind, but again, given a good deal of patience and a lot of people with nothing much else to do, you can accomplish amazing feats.)

So that's what I was shooting for in the dramatization above-- the fact that while there's a good deal of science involved in the construction of Newgrange, it was unquestionably human science. People looked at the motion of the rising sun through the year, thought about a monumental way to use the sun's motion to mark a significant date, tested and refined their model over many years, and passed that knowledge down through generations. And in the process, they built a marker that still functions perfectly five thousand years later.

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(Part of a series promoting Eureka: Discovering Your Inner Scientist, available from Amazon, Barnes and Noble, IndieBound, Powell’s, and anywhere else books are sold.)