Stonehenge Astronomy IV: The Stars

Everyone knows about the entrance into Stonehenge from the northeast. Fewer people know about the other entrance to the site that opens due south of the circle. This might be evidence of an interest in the stars at Stonehenge.

Normally I’d be loath to claim there were stellar orientations at a site. It’s not that I don’t think stellar alignments weren’t used in prehistory. It’s just that there’s a sky full of stars. How do you prove that a stone row was aligned on star A when star B would be rising in the same direction a few hours later? The reason I think this might be a stellar alignment is because I’ve been thinking, “How do you work out where south is?” If all goes well we’ll have an experiment set up at the Stonehenge model to show how. It’s another one of these things where it seems people weren’t inside the monument looking out. Rather they were outside the monument looking in. If you look to the southern sky there’s not a lot of clues as to where south is. If you look to the northern sky though it’s a different matter. If you watch through the night you’ll see the stars turning around a point up in the sky (assuming you’re not reading this in the southern hemisphere). These days that point is pretty close to Polaris, though four or five thousand years ago Polaris was quite a way off from this place.

The experiment I’d like to see set up, if the weather holds, is a time-lapse or long exposure shot of Stonehenge from the south. You won’t need to leave the camera there all night. If you leave it just 25 minutes you should see the stars do something like in the picture below.

The Robert Ferguson Observatory. Originally uploaded by astrovine.

This is an experiment you can do yourself if you have a manual exposure camera, a slow film and a site away from light pollution. What should happen is that the stars will trace out arcs. If you left the camera for twenty-four hours, and there wasn’t a Sun to obliterate the night sky during the daytime, then you’d see the star trails form concentric circles around the North Celestial Pole. This is because of the Earth turning on its axis once every twenty-four hours.

One possible way of getting the second entrance exactly south then would to be to observe the stars over a few nights, see which point in the sky they were rotating around and then move round the henge until it was directly over Stonehenge. The place where you were standing would then be the southernmost part of the henge.

I can’t be certain this is how it was done. I can’t even be certain that the entrance was deliberately placed accurately in the south. Maybe it was just a handy location for an entrance. But if it was a deliberate cardinal entrance then this would be a plausible way to align it. —–