1: Stonehenge and the Moon

Stonehenge, even now, after so many people have investigated and written about it, seems to be a puzzle. The most basic questions still remain unanswered - the real purpose of this ancient construction, why it was built in that particular location and who built it? One book which seems to throw an interesting spotlight on the subject is by Gerald Hawkins, entitled Stonehenge Revisited. Following his first book on the subject, Stonehenge Decoded, the sequel contains a detailed analysis of the alignment of the stones on the site when related to the various star systems seen in the night sky.

Due to the motion of the Earth round the Sun and the passage of the Sun through our galaxy, what can be seen in the night sky from Earth has not always been the same. Over a period of a few thousand years it has changed considerably, but by studying the motions of the planets and stars, astronomers have been able to estimate what the night sky looked like back to nearly 5000 BC. Professor Hawkins related this information to the unique combination of alignments he had found at the site and was able to demonstrate the accuracy of the original construction date established by archaeologists.

Professor Hawkins showed quite clearly that Stonehenge could be used to calculate when the next solar or lunar eclipse would occur. This was in addition to being an astronomical observatory and solar/lunar clock, able to check the time of year rather accurately. He found that, for Stonehenge, at 51.2° north latitude, a rectangle of stones was necessary to identify the extremities of the Sun and Moon arcs in the sky and that this became a ‘pushed-over’ parallelogram as one moved either north or south. Figure 1.1 shows the various solar and lunar events plotted by the standing stones SS91, SS92, SS93 and SS94 and it is clear that these four stones form a rectangle. He further found that he was able to identify only one other latitude which yielded a distinctive shape, the hexagon, and that was at 30° latitude. This passes through northern Egypt where the Pyramids are located. Figure 1.1 A plan view of Stonehenge, showing the alignments achieved by the rectangle of stones created by SS91, SS92, SS93 and SS94.

Another area examined by Professor Hawkins was the Aubrey ring or circle. It is curious that the four stones, which formed the rectangle, were placed on this circle as though the two were inter-related. The circle of 56 holes, found by John Aubrey in the seventeenth century, is 285 ft. (86.9m) in diameter, and no hole is more than 21 ins. (0.53m) from the true geometric circle.

To be able to appreciate the theories put forward by Professor Hawkins, it is worth examining more closely the motion of both the Sun and Moon as they appear from the Earth from the northern hemisphere. We know that the Earth spins on its axis and completes one spin each day. It also orbits the Sun and completes one orbit in a year. From a viewpoint on the Earth, the Sun describes a regular arc in the sky. This regular arc, however, is not quite the same throughout the year and the reason for this will be looked at a little later.

Figure 1.2 The Moon rising and setting during Winter
Over a series of winters lasting 18.61 years, the rise and set positions of the Moon on the horizon vary. The diagrams above and below represent the extremes reached at the beginning and end of this period. After a further 18.61 years they proceed back to the situation in the upper diagram, which shows the positions reached in the year of the 'major lunar standstill'. The horizon is at latitude 55° (English/Scottish border).

The Moon orbits the Earth, and while it appears to do so once a day, it actually takes nearly 30 days to complete one orbit. During the winter months, the Moon rises on the eastern horizon between north and east, setting between north and west (see figure 1.2). This means that the Moon describes a high arc in the sky, quite the opposite of the Sun which, during daytime, is appearing to follow a low arc across the southern sky.

During the summer months, the Moon rises between east and south, setting between west and south, and it describes a much lower arc in the southern sky which is similar to that of the Sun during the winter (see figure 1.3). In contrast, the Sun during the summer appears high in the sky at midday.

Figure 1.3 The Moon during Summer
A similar pattern of rise and set over a period of 18.61 years is shown, the diagrams above and below representing the extremes. Here, however, the Moon is rising and setting in the southern sky. The position reached in the year of the 'major lunar standstill' is shown in the lower diagram. Again, the horizon is at latitude 55°.

The rising of the Moon in any given month in succeeding years does not occur in exactly the same place on the eastern horizon, except after a period of, on average, 18.61 years. In searching for the lowest whole number which would be the best fit for monitoring this cyclic nature of the moon’s rise and set, Professor Hawkins found that 56 (18.61 x 3) was the most appropriate, which agrees with the number of holes in the Aubrey ring. He then proceeded to describe a method by which the holes could have been used to monitor when the Moon would reach the extremities of its rising and setting positions.

The relationship between the Sun, the Earth and the Moon is graphically illustrated by the various phases of the Moon, which can be seen in the clear night sky, except in the two days preceding the new moon. Figure 1.4 shows these phases of the Moon and how they are created with the light from the Sun. During a total eclipse of the Moon, a certain amount of light is refracted onto the surface of the Moon via the Earth’s atmosphere and for this reason the Moon does not disappear completely.

Figure 1.4 The various phases of the Moon

As the angle of the plane of the orbit of the Moon round the Earth to the plane of the equator varies by ten degrees, or ±5° to the plane of the orbit of the Earth round the Sun, the Moon usually passes either above or below the shadow cone at the time of the full Moon (see figure 1.5). This angular variation goes from one extreme to the other over a period of 18.61 years and accounts for the differences of rise and set illustrated in figures 1.2 and 1.3.

Figure 1.5 Relationship between the Sun, Earth and Moon showing how an eclipse of the Moon can occur

A lunar eclipse is produced when the Moon passes into the shadow cone. The full Moon occurs when it is exactly opposite the Sun in the sky, as shown in figure 1.4. Astronomically it is a split-second event, although when viewed by the naked eye, an observer would not see much change in the full moon for about three nights. As the Moon passes in front of the glare of the Sun, there is a period of invisibility for one or two nights. The month therefore contains 27 or 28 phases (nights), plus 1 or 2 no-phase or invisible nights, making a total of 29 or 30, which averages out to 29.53.

Figure 1.6 Winter in the Northern Hemisphere

So why doesn’t the Sun describe a regular arc in the sky? At the winter solstice (December 22nd in the Northern Hemisphere), the axis of spin of the Earth is inclined at an angle of 113° 45’ to a line joining the centres of the Earth and the Sun (see figure 1.6). At the summer solstice (June 21st), this axis is inclined at 66° 15’ to that same line, causing the Sun to appear higher in the sky, giving longer daylight hours and hence higher daytime temperatures (see figure 1.7). When the axis of spin appears at right angles to the plane through the equator, the orbit of the Earth is at equinox, as the Sun appears directly overhead at 12 noon anywhere on the equator.

Figure 1.7 Summer in the Northern Hemisphere

So where does that leave us in our quest for the ancient wisdom? It is clear that considerable knowledge had been built into Stonehenge since the type of construction does not lend itself to rapid adjustment. From the evidence on the ground, the builders of Stonehenge had a detailed understanding of the complex celestial cycles. They also had the computational skills to select an exceptional location (witness the rectangle of stones) and construct a sophisticated device for the recording and prediction of these cycles.

But it is still not known who built it or why it is placed in that specific location. Without such information, its true purpose cannot be ascertained, but by accepting the proposal that the site contains in-built knowledge, then one begins to ask much more pointed questions. Why is it that we cannot read about the true purpose of this site, for during its construction, which occurred over several phases taking many centuries, its purpose would have been all too clear? Where has this information gone? Furthermore, information built into its design would have taken some considerable time to amass, probably over many generations. Where did this information come from and who gathered it?

Professor Hawkins had found strong evidence that Stonehenge was a solar and lunar clock, able to check the time of year quite accurately. It could therefore be regarded as a ‘monolithic calendar’. Since stellar and lunar observations were essential for the construction of such a calendar, was this also the basis of ancient calendars around the world?

The quest continued.