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Astro-archeology

Astronomers tend to concentrate their efforts on the future, on new discoveries, and furthering existing techniques and knowledge. This is a valuable thing, but there is also much to be learnt from the past. Dave Goode casts his beady eye back four thousand years for a look at the fascinating world of astro-archaeology.

No journey back into British prehistory could possibly start anywhere other than the world famous stone circle at Stonehenge in Wiltshire. Astronomical explanations of these curious circles were popular in the nineteenth century, but were regarded as cranky, or misguided, at best. The work of Norman Lockyer, Director of the Solar Physics Laboratory, changed that attitude, and brought astro-archaeology into the scientific mainstream. He published "Stonehenge and Other British Stone Monuments Astronomically Considered" in 1906, and the floodgates opened. Nowadays, it is not unusual for people to come up with fantastic theories that only an idiot would believe. There are those who, in all seriousness, believe that they were landing places for alien craft from outer space! I intend to pursue a strictly scientific interpretation, though, and keep my feet firmly on the ground.

Lockyer believed that the Neolithic and Bronze Age peoples were a lot more intelligent than we generally give them credit for today. They would carefully select a site and then arrange the stones so that its major axis pointed at the position in the sky that a planet, or bright star, or the Moon would assume at a particular time on a given date. Sometimes distant mountain peaks or a single standing stone or cairn, a mound of smaller stones, would serve as a foresight to ensure correct observation.

Stone Henge Assuming the correct position, presumably at the centre of the circle, would have presented quite a problem for the observer. Unless the foresight object was a large distance away, standing less than a metre from the correct position could result in an error of four or five degrees of arc in the sky, a sizable error. To put this in perspective, if we precess the RA and declination coordinates for the bright star Rigel (Beta Orionis), and then introduce a margin of error of four degrees, this corresponds to almost one thousand years difference for a sighting on a given date!

Radio Carbon Dating has suggested the period in which most of the circles were built. The majority went up between about 2500 BCE and 1600 BCE (Before the Common Era), a period at which the night sky looked considerably different to today. I have produced two accompanying charts that show the area around Orion today, and in 2500 BCE to indicate the effects of precession.

While sighting of bright stars presents logistic difficulties, one fact remains indisputable. Most of the earliest monuments are connected with the Sun, especially with its rising. Most burial mounds, or barrows, have the actual positions of the body at the eastern end of an East-West axis, and megalithic tombs were always built with their entrance between northeast and southeast, the maximum and minimum rising point of the Sun during the year.

The astronomical connection seems to have started with the Sun, the most obvious and easily observed celestial body. Later, when the people had accumulated more knowledge of the night sky, they refined their techniques and could build the great observatories that we now dismiss as "stone circles". Worship of the Sun was prevalent in many societies, from the dawn of civilisation even to the present day. Early civilisations viewed the Sun as the giver of life, and the Moon as a lesser god, often the consort or wife of the Sun. They naturally looked forward to the solstice festivals, and to the end of winter, and set great store by appeasing the Sun-god with sacrifices, often human!

The astronomical character of the circles is only a part of the story, however. The circle may have symbolised a place of safety, a place where man was protected from the spirits, and sacred rites took place within the circles. Several circles in Britain have altars that may have been used for sacrifices, and I have visited several prehistoric temples contemporaneous with Stonehenge on the island of Malta. The Maltese sites are extremely well preserved, and have well defined chapels and altar stones, many of them exactly the right size for a human! The circles were clearly a very important part of the community's everyday life, as shown by the efforts and care put into their construction.

Stonehenge and Avebury, eighteen miles to the North, stand at the central position in prehistoric Britain. The Avon and the Thames are nearby, and the area forms a natural hub from which British civilisation radiated. East was the Thames and then East Anglia and the sea, southwest was Cornwall, West was the Avon, and Ireland, northwest was Wales, and the main routes to the North of England and Scotland. Excavations at these two sites have turned up stone axes from Cornwall, Wales and even Cumbria, copper and gold from Ireland and jet-stone from Yorkshire. Wiltshire was obviously a central area, and Stonehenge a very important site. Stonehenge is the largest site in Britain requiring enormous effort in its construction, and it seems unlikely that it could have been built with just local labour.

Stonehenge started life as a simple henge, a ring of stones, built on a gentle chalky slope around 2700 BCE. Over the next one thousand five hundred years many additions were made as Stonehenge gradually assumed its central, almost cathedral role. During the mid-second millennium, about 1500 BCE, a major addition was undertaken, which confirms the astronomical nature of the site. Five trilithons, an arrangement of two upright stones and one lintel across the top of them, were transported the twenty miles from Marlborough Down. They were arranged in a horseshoe shape that had its open end pointing northeast, the direction of sunrise in Winter. There is an extension out from the original outer ring of stones only in that direction, providing a twelve-degree arc of vision from the horseshoe at the centre. There is evidence of an area in which wooden stakes were sunk at the point where the arc leaves the outer ring and the extension begins.

The arc of vision subtends 10 degrees, from 41 degrees at the northerly edge to 51 degrees at the easterly. These extremes mark almost exactly the maximum winter moon rise at 41 degrees and the midsummer sunrise at 51 degrees. It seems likely that the wooden stakes served as graticules to mark the passage of Sun and Moon and pinpoint a desired instant exactly. C.A. Newham pointed out, in the Yorkshire Evening Post on the 16th of March 1963, that the latitude of Stonehenge is very significant. It is such that the extreme northern and southern rising and settings of both the Sun and Moon are at right angles to one another. This is a topocentric phenomenon that occurs only at Stonehenge. A mile or so in any direction will result in the alignment resembling a skewed parallelogram rather than a perfect square.

Around 2150 BCE two new inner circles were built concentrically with the outer. Whereas the original stones were quite local in origin, these new stones were brought from the Preseli Mountains in South West Wales. Each stone was worked into a four-ton block, and eighty-two were brought by ship and land the 200 miles to Stonehenge.

Some two miles from Stonehenge, on the banks of the Avon, a huge earthwork was excavated, almost 100 metres across and circular. Here there must have lived a large population, in the traditional round wooden huts of the time. The area is now known as Durrington, and is so huge that civil engineers investigating the site estimated that close to one million hours of labour would have been needed to construct it. Even with several hundred people working together this would have taken years, and a similar but smaller bank at Stonehenge would have taken thirty thousand hours of labour.

The sighting of the midsummer sunrise and midwinter moon rise must have been very important to these so-called primitive people. They went to great lengths to choose the site carefully, and no effort was spared in its construction.

The stones that make up the horseshoe in the centre, although they came only from Marlborough Down about twenty miles away, weighed twenty-six tons each, and there were seventy-seven of them. Between Marlborough and Stonehenge are downs, slopes, streams and the punishing Redhorn Hill, and it seem unlikely that they could move more than one stone per year!

Stonehenge was a magnificent achievement of architecture, astronomy and sheer sweat! What is fascinating is that the astronomers could allow for precession over the centuries. As Stonehenge evolved, the axis of its construction changed too. The centre point, marked by a stone, moved 30 centimetres to adapt to the change in the midsummer sunrise. Other changes show how the people's religion changed over the centuries. Originally, they were interested in the midsummer rising of the Sun, but the emphasis changed in later years to the midwinter sunset, and this is reflected in the construction of the later parts. For the people of Stonehenge, as for so many others then, from South America to Siberia, the Sun was their god. They worshipped the Sun as the source and giver of life, appeasing it with elaborate rituals and sacrifices. They were devoted to the Sun-god and his wife, the Moon, mistaking the Creator for his creations.

I have concentrated on Stonehenge so far, but there were many other circles in prehistoric Britain. The rest are all smaller, and more often than not in a poor state of repair, and Stonehenge was, and still is, the primary site. The circles are concentrated in the West of Britain, with few in East Anglia and along the East Coast. In Scotland, however, the reverse is true. The Highlands made western Scotland inaccessible, and most circles are found on the flatter Eastern coastal plains. I have produced a map to illustrate the distribution of Stone Circles throughout Britain.

Most circles appear to share a common astronomical theme, being arranged to observe the Sun and Moon rise and set. There is little evidence of any planetary observation in the British culture. It seems that the early peoples knew well and understood in depth the motions and orbits of the Sun. How paradoxically this compares with the Middle Ages, and Reformation times when anyone daring to contradict the Christian Church's opinion was tortured, burned alive, stoned or ostracised. The Roman Catholic Church had a list of proscribed books which contained any works that made reference to the heliocentric theory of Copernicus. Anyone in possession of one of the books on this list was automatically excommunicated if a spot of torture did not persuade them to recant. Almost unbelievably this list was not repealed until the 1830's!

Unfortunately space has beaten me again, just as I was getting going! For those whose appetites I have whetted, Amateur Astronomy & Earth Sciences magazine regularly includes articles on the astronomy and technology of ancient cultures including up to the minute research by cutting-edge authors such as Graham Hancock ('Fingerprints of the Gods') and Robert Bauval ('The Orion Mystery'). Why not buy a copy today, or better still, subscribe.


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