Stonehenge and Other British Stone Monuments Astronomically Considered

by Sir Norman Lockyer

In order to obtain some measurements to test the orientation theory in Britain, I found that Stonehenge is the ancient monument in this country which lends itself to accurate theodolite work better than any other. Mr. Spence’s excellent work on astronomical lines at Stenness, where the stones, till some years ago at all events, have been more respected than further south, suggested a beginning there, but the distance from London made it impossible.

Avebury and Stanton Drew are well known to a great many archæologists; there are also other very wonderful stone circles near Keswick and in other parts of England; but unfortunately it is very much more difficult to get astronomical data from these ancient monuments than it is in the case of Stonehenge, one reason being that Stonehenge itself lies high, and the horizon round it in all directions is pretty nearly the same height, so that the important question of the heights of the hills along the sight-line—a matter which is fundamental from an astronomical point of view, although it has been neglected, so far as I can make out, by most who have made observations on these ancient monuments—is quite a simple one at Stonehenge. Hence it was much easier to determine a date there than by working at any of the other ancient remains to which I have referred.

In orientation generally—such orientation as has been dealt with by Mr. Penrose and myself in Egypt and in Greece—the question frequently was a change in direction in the axis of a temple, or the laying down of the axis of a temple, by means of observations of stars. Unfortunately for us as archæologists, not as astronomers, the changes of position of the stars, owing to certain causes, chiefly the precessional movement, are very considerable; so that if a temple pointed to a star in one year, in two or three hundred years it would no longer point to the same star, but to another.

These star observations were requisite in order to warn the priests about an hour before sunrise so that they might prepare for the morning sacrifice which always took place at the first appearance of the sun. Hence the morning star to be visible in the dawn must be a bright one, and the further north or south of the sun’s rising place it rose, the more easily it would be seen. Some stars so chosen rose not far from the north point of the horizon. The alignments with small azimuths referred to in the British circles ([p. 36]) I believe to be connected with the Egyptian and Greek practice.

Acting on a very old tradition, some people from Salisbury and other surrounding places go to observe the sunrise on the longest day of the year at Stonehenge. We therefore are perfectly justified in assuming that it was a solar temple used for observation in the height of midsummer. But at dawn in midsummer in these latitudes the sky is so bright that it is not easy to see stars even if we get up in the morning to look for them; stars, therefore, were not in question, so that some other principle had to be adopted, and that was to point the temple directly to the position on the horizon at which the sun rose on that particular day of the year, and no other.

Now, if there were no change in the position of the sun, that, of course, would go on for ever and ever; but, fortunately for archæologists, there is a slight change in the position of the sun, as there is in the case of a star, but for a different reason; the planes of the ecliptic and of the equator undergo a slight change in the angle included between them. So far as we know, that angle has been gradually getting less for many thousands of years, so that, in the case of Stonehenge, if we wish to determine the date, having no stars to help us, the only thing that we can hope to get any information from is the very slow change of this angle; that, therefore, was the special point which Mr. Penrose and I were anxious to study at Stonehenge, for the reason that we seemed in a position to do it there more conveniently than anywhere else in Britain.

Fig. 8.—The original tooling of the stone protected from the action of the weather.

But while the astronomical conditions are better at Stonehenge than elsewhere, the ruined state of the monument makes accurate measurements very difficult.

Great age and the action of weather are responsible for much havoc, so that very many of the stones are now recumbent, as will be gathered from an article by Mr. Lewis, who described the condition of the monument in 1901, in Man.