Aubrey Holes - Archaeoastronomy and The Aubrey Holes

Archaeoastronomy and The Aubrey Holes

The astronomical readings of the holes are largely a product of the interpretation of them as being simple pits without any structural features. This approach has required finding an explanation which tends towards the theory that the holes were repeatedly dug, filled and redug and excludes possibilities relating to any possible timber posts standing in them. The theory that they may have been used to hold temporary markers for use in astronomical observations gained credence in the 1960s.

An early attempt to analyse the positions of the Aubrey holes was undertaken by Gerald Hawkins a professor of astronomy at Boston University in the 1960s using an IBM 7090 computer. In his book Stonehenge Decoded, Hawkins argued that the various features at the Stonehenge monument were arranged in such a way to predict a variety of astronomical events. He believed that the key to the holes' purpose was the lunar eclipse, which occurs on average about once a year on a 346.62 day cycle. Lunar eclipses are not always visible as the moon may be below the horizon as it moves across the sky, but over 18 to 19 years (18.61 years to be precise — error: it is 18.03) the date and position of a visible eclipse will return to its beginning point on the horizon again. As the motion of the moon's orbit also causes it to work its way across the sky on an 18.61 year cycle in what is known as the journey between major and minor standstill and back, the theory that this period was both measurable and useful to Neolithic peoples seemed attractive. Lunar movements may have had calendrical significance to early peoples, especially farmers who would have benefited from the division of the year into periods which indicated the best times for planting. 18.61 is not a whole number and so it cannot be used to predict an eclipse without precision equipment and using only crude stones or timber posts in a circle instead. Hawkins' theory was that three 18.61 year cycles multiply out to 55.83 however, which is much closer to an integer and therefore easier to mark using 56 holes. Hawkins argued that the Aubrey Holes were used to keep track of this long time period and could accurately predict the recurrence of a lunar eclipse on the same azimuth, that which aligned with the Heel Stone, every 56 years. Going further, by placing marker stones at the ninth, eighteenth, twenty-eighth, thirty-seventh, forty-sixth and fifty sixth holes, Hawkins deduced that other intermediate lunar eclipses could also be predicted.

More recent examination, notably by Richard Atkinson, has proved Hawkins largely wrong as it is now established that the different features at the monument that he tried to incorporate into many of his alignment theories were in use at different times and could not have worked alone. The lateness of the installation of the Heel Stone being the final nail in the coffin. Furthermore, the 56 year period is not in fact a reliable method of predicting eclipses and it is now accepted that they never repeat their date and position over three consecutive 18.61 year-long lunar cycles. Hawkins' theories also required strict observance of the phases of the moon which further complicated predictions using his model.

In 1966 Sir Fred Hoyle examined the arguments in favour of an astronomical purpose for the holes and concluded that the 28 day lunar cycle could still have been indicated by moving a marker stone representing the moon anticlockwise by two holes every day, ending up with 56 holes in total. By moving another marker anticlockwise two holes every thirteen days and which represented the Sun, an annual journey around the circle could also be made. Two further marker stones would also have had to be moved round three holes per year to represent the points where the moon (or rather its marker) crossed the Sun marker's path. Hoyle proved that this could have been used to produce a much more reliable method of predicting eclipses as whenever the moon and sun markers are directly opposite each other and the other two stones occupy those same opposing points, an eclipse can be guaranteed. This also has the additional benefit of not needing any standing stones to be present at the site.

Although less complex and romantic than Hawkins' 'stone age calculator' such a technique is certainly feasible if only in theory. Much more elaborate predictive practices have also been suggested for the holes although all these methods, including Hoyle's, require a high level of astronomical awareness and a grasp of some very abstract concepts including knowing where and when to first position the stones around the circle. It has also been pointed out by R. Colton and R. L. Martin that simpler methods exist, based on observing the position of each moonrise, which would have worked just as well and which would not require moving numerous markers amongst 56 holes. This diminishes the astronomical significance of the number of the Aubrey Holes and their circular arrangement and tends to suggest that any astronomical purpose for the site may have been no more than symbolic.

On astronomical symbolism several analysts from Gerald Hawkins to Anthony Johnson (ref. 3 ; pages 259-260) have noted that Plutarch ( in the Moralia, V) reported that Typhon / Seth in Egyptian and Greek myth was identified as the shadow of the Earth which covers the Moon during lunar eclipses. Plutarch further records that the Pythagoreans symbolically associated Typhon with a polygon of 56 sides. The connection of 56 to lunar eclipses is explicit.