Stonehenge Astronomy VI: Comets and Meteors

You may have noticed that the entries are getting more speculative as they go on. This next idea by Duncan Steel was panned by the readers of British Archaeology (scroll to bottom) when it was published there, but I think it’s worth hearing. It is possible that there could be a connection between Stonehenge and transient phenomena like comets or meteors.

The basic assumption in archaeoastronomy is that the night sky we have today it pretty much like the nights skies the ancient had. The stars may have shifted position over time. The Sun doesn’t quite swing as much across the horizon, it’s lost about one sun width at either extreme. But the assumption is that if you went back to the time of Stonehenge four or five thousand years ago the sky would look more or less the same. The stars would be just as bright and would make the same patterns in the sky. Duncan Steel has suggested that this might not be accurate and comets are to blame.

Comet Hale-Bopp. Did a sister comet terrify Stone Age people into building Stonehenge? Photo by Arlo Forbes.

Some other people have suggested that Stonehenge could have tracked comets. Steel doesn’t think so and neither do I. Comets can appear at any time from anywhere. The bright ones, the ones that make an impression have incredibly long periods. Halley’s Comet is quite short being just seventy-six years but even so without written records this kind of data simply couldn’t be stored to predict comet returns. What is interesting is that while we might not see them, we hit their tails on an annual basis.

Each time they pass by the Sun comets leave a trail of debris. Dust grains fly off the comet and orbit in the same path like a cosmic smudge around the Sun. Over the centuries the comets lay down a ring of tiny particles that litter their orbits. When the Earth passes through one of these dust paths, the particles smack into the atmosphere at high speed. They are vaporised and you can see them in the sky as streaks of light, meteors.

Leonids as Means to Describe Phosphenes. Photo uploaded by Andrew Coulter Enright.

The particles are in parallel orbits, but they are a long distance away so, rather like railtracks when you look along them, they appear to be coming from one point in the sky. Also because they intersect with the Earth’s orbit at a specific point, you can predict when they’ll happen. The next major shower will be the Perseids, on August 12. One possible use for Stonehenge would be to keep track of when meteor showers would happen.

This could be useful when you stop thinking about meteor showers and start thinking about meteor storms. The Leonids are famous for terrifying people into thinking the world is ending. When 10,000 meteors are striking the atmosphere each hour it looks like the sky is falling in. Imagine the social benefits of being able to predict this kind of event.

The problem is we don’t know if this happened in the past. We don’t know enough about cometary orbits to know when meteor showers happened in prehistoric times, nor how intense they were. However looking back over five thousand years it is plausible that there were periods of intense meteoritic activity. When we do learn more about comets it may you may hear more about meteor showers being tied to certain historical events.

Update 17/11/2005: Following a post on The Treehouse and the Cave the meteor image has been re-labelled. The original label Phosphenes Leonids (meteors) was lazy copying of the ALT text with the qualifier (meteors) for those who don’t know what a Leonid is when I found the image on Flickr. Apologies to Andrew Coulter Enright for any distress caused. —–