A fairly common theme in astronomical explanations of ancient sites is that they were set up with a connection to the solstices. The statistical evidence leads me to think that it’s right, but it poses a serious problem, which day is the solstice? That should be an easy question to answer, it’s the day when the sunrise or sunset reaches it’s farthest position north or south. The reality is harder. The point where the sun rises over the horizon in the morning changes over the course of a year in a similar way to the way a pendulum swings. When it’s passing through the middle the change is large, about one sun-width each morning. When it reaches the solstices though the sun slows down and appears to stop in the same place for a few days. There is change, but it’s tiny about 1/30th of the sun’s width each day. That’s where the name solstice comes from. It’s derived from the Latin sol from sun and sistere to stand still.
It’s because this effect is so difficult to view that many people argue for high-accuracy observation of astronomical events. In some ways this can make arguments a bit circular. How do we know a place is an observatory? It’s because it must have been important to get the exact day of the solstice. How do we know that the exact day of the solstice was important? Because the extremely high accuracy makes it so likely.
There’s some highly intelligent and simple methods people have proposed for observing the solstice. I like one example used at Brainport in Scotland where it’s been proposed that a marker slightly off-solstice was used. If you do that then you can more accurately count the days between sun’s passes of the marker. The next year you know that the solstice is half that number of days after the first pass. It’s possible and it also allows a flexible marking of the solstice to coincide with lunar months. If the alignment to the solstice is symbolic and for special effects in the ceremony then you can hold the solstice event on a few days. The problem is without historical evidence it gets hard to argue whether or not a very specific explanation is convincing.
In Ancient Greek Agriculture: An Introduction by Signe Isager and Jens Erik Skydsgaard they do find historical evidence of the solsticial observation over a standing stone. From on page 163 they talk about a stele from Crete with this inscription.
Patron set this up for Zeus Epopsios. Winter solstice. Should anyone wish to know: off ‘The little pig’ and the stele the sun turns.’IC IV.11
They go on to explain that ‘The little pig’ was a rock jutting out at some distance away in the water. They argue that it indicates that it was a foresight and the stele a labelled backsight for observing the winter solstice.
The reason Isager and Skydsgaard argue that the stele was set up for the winter solstice was that they think the rising of Orion was the marker for the summer solstice, which is easily observable and so a marker wasn’t necessary. I’ve argued elsewhere that Delphinus would make a suitable marker for the winter solstice, and it’s found mentioned surprisingly often for a small and faint constellation on parapegmata, stone calendars with holes for a peg which would mark the day.
Nonetheless it is useful and rare to find an astronomical site with the instruction manual for how it should be used. Thanks to Prof. Graham Shipley for passing along the reference.
Things to do: That kind of observation in Crete doesn’t automatically mean that similar observations were made in Greek Sicily. What would be helpful would be to look up the inscription and see when it dates from. If it’s early then that could be more persuasive, because it’s thought that settlers from Crete came to Sicily. If that’s the case then it’s more likely that the practice transferred with them.
Update 8 Sept 2010
If you’re interested in this inscription, there’s a discussion at the Itanos blog (in French) that’s worth reading. It includes another historian talking about Zeus Epopsios that I’d missed.