mindlace

The solstice is upon us, and in discussing it with some folks online I realized people have a fairly fuzzy concept as to what it actually is. As someone who has come to feel that reflecting upon the cycles of nature is somewhere between important and holy, I’ve given the matter much thought.

Many ancient peoples thought about the matter a great deal, and constructed a wide variety of stone instruments to measure when the solstice occured. There is general consensus that a number of these cultures engaged in some sort of practice when the instrument was active, and observation indicates they were only active twice a year, though some of the artifacts respond to other times as well. Precisely what practices they engaged in, and which of those are germane to our present context, is left as an exercise for the reader.

The modern take, exemplified by the archaeoastronomy site, suggests that the solstice is a precise moment, calculable to within one minute of resolution. This implies that the solstice is an orbital relationship between the sun and the earth. This sounds nice and scientific, but unlike the ancient version, there’s no way to directly measure when this moment would be (from earth) and if you make precise enough measurements to actually predict when the earth will be in the same relationship to the sun, you find out that it doesn’t really happen. A bright fellow named Malenkovich came up with an amazing way to date old ice cores by taking advantage of the fact that the earth’s orbit is irregular.

So the number you see on the archaeoastronomy site isn’t based on observation; it’s extrapolation from an average earth orbit computed as if the earth and the sun were the only two bodies in the solar system.

So what’s the solstice about? To me, it’s about a relationship between the sun and the earth, as exemplified by the two days each year when the sun is in a particular relationship to a patch of ground on the earth. I don’t think the modern, abstract and inferential (but pleasingly ‘objective’) notion of orbital relationships has concrete meaning, and for a variety of reasons I think direct encounters with the lived world are superior to mere ideas as a foundation for my relationship with all-there-is.

Ancient solar observatories like stonehenge were basically giant immobile sextants that ‘activated’ when the sun at the highest point in the sky at different times of the year. If we’ve agreed that observing the sun is better than Keplerian projection for fixing the moment of the solstice, the question becomes: how accurately can the sun be measured?

Interestingly, the answer is that most ancient monuments do a better job than just about anybody bothers to do with the solstice these days. The US Naval Observatory has a page where you can get sunrise/sunset dates for your area; if you look to around today, you’ll notice that there are likely 2-3 days with the same rise/set times. The difference in position of the sun at apogee varies by an astonishingly small amount in 2-3 days- a small fraction of the apparent width of the sun itself. Unless you build yourself a remarkably precise solar observatory, you can’t differentiate between those days.

I would argue that it is this 2-3 day interval that is the genuine “solstice”. So feel free to party today, tomorrow, or perhaps even Saturday and feel safe that you’re observing the solstice as it is happening.