STONEHENGE
An Extract Of An Essay.

There are many stone circles all over North Western Europe, but none have provided as much incentive to research as Stonhenge. Standing isolated on the Salisbury Plains, the stones have been erected in an area full of ancient burial grounds, monoliths and ancient man-made hills. The area was obviously at one time a centre of quite a successful civilisation. Stonehenge seems to mark the culmination of their understanding of astronomy, as well as having probable religious significance. A lot of archaeological research has been done into the building of Stonhenge and it is now known that the stones were erected in three stages: The earliest is called Stonehenge I, and the latest is called Stonehenge III. It is Stonhenge III that is visually the most impressive, consisting of the Trilithons, two stones stood upright with one laid across the top of them. These trilithons are laid out in a circle within both larger circles of Stonehenge I and Stonehenge II. Stonhenge II is a circle of stones laid out within the circle of Stonhenge I. It appears to have never been completed.

It is Stonehenge I that provides the most interesting clues to the fact that this early civilisation had quite complex understanding of astronomy, especially in relation to the Moon and the Sun. Built around 2700BC, its most obvious alignment which is still observed by many, is the rising of the Sun on Midsummer's day. Today it is modern Druids that celebrate this annual ritual, although Stonehenge was built well before the original Druids. The stone that marks this event is known as the heel stone. It stands outside the main circles at the end of an avenue which carries on in a straight line for approximately half a mile, in an almost North Easterly direction. On midsummers day at about 5:00am the Sun rises above the horizon and from within the centre of the circle its first rays of light appear directly above the heel stone. With the wonders of modern technology I can recreate the positions of stars, planets, Sun and Moon for the year approx. 1500B. By watching the Sun rise on the software for each day around the period for which I expect the longest day to be, I can judge to within a day or two when the Sun would have reached its most Northerly rising point. This also applies to the setting of the Sun and the rising and settings of the Moon. By positioning the mouse pointer on the object I am studying , I can obtain the azimuth position (the degrees from North for an object on the horizon). Table 1.0 was obtained by observing the Moon rise each year for the most Northerly rising point in the Month before Midwinters day. The builders of Stonhenge had observed much more, however; although sunrise on Midsummer's day was probably the most important ceremonially, other alignments have also been found that are agreed to be too accurate to be mere coincidences. Stonehenge I when built consisted of a ditch and a bank, probably about 8 feet high and 300 feet in diameter; inside this circular ditch was a ring of 56 holes, known as the Aubrey holes after John Aubrey who discovered them in the seventeenth century. These holes had been dug and then filled after fires had been lit in them. Also in stage I, four marker stones were placed around the ring, two of these on mounds. The following simplified diagram of Stonehenge showing the astronomical alignments as they would have occurred about 3500 years ago. The most obvious alignments are those between the stones numbered 91, 92, 93, 94. these correspond to the Moon setting at its most Southerly point, Moon rising at its most Northerly point, the Sun rising at its most Northerly point and the Sun setting at its most Southerly point. As can be seen from the diagram, these four alignments form an almost perfect rectangle. From research it would appear that there are only two areas on Earth where this can happen, the area between Oxford and Bournmouth and the area around the Falkland Islands. Whether the site was deliberately chosen for this alignment or whether this was an accident of construction is open to debate.

A more detailed theory of the usage of Stonehenge I has been proposed by two writers, Gerald hawkins, 1965 and Fred Hoyle 1972, the latter using the former as a basis for his theory. Fred Hoyle has I think the more plausible explanation of how observations were made. Both theories are based on the usage of the 56 holes incorporated in Stonhenge I, to predict eclipses. I will attempt to explain how Hoyle's theory works. Both theories are based on predictions of the path of the Sun and The Moon by separate computers for the period about 2000BC. The Earth wobbles on its axis about once every 25800 years; therefore it would take an awful lot of observations to notice any significant change in the Earths tilt with respect to its orbit around the Sun. The Moon also has a variable tilt. This is much more noticeable, swinging from 61^o to 71^o, from one month to the next in the rising or settings of the Moon. The time taken for the total swing in the tilt, to vary from one extreme to the other and back again is the is period of 18.61 years. It has been found that the yearly positions for the extremes of sunrise and sunset are apparent at Stonehenge, also the Monthly swings in the position of the Moonrise are apparent. More obvious though are the fluctuations in the 18.61 year cycle for the Moon which define its most Northerly point of rising and its most Southerly point of rising. The two extremes of the 18 year cycle (9.3 years apart). I used SKYGLOBE software, an ordinance survey map, a Stonehenge plan and a compass to check the positions of the rising of the Moon from one extreme to the other during this period and drew my results on a sheet of paper . My results are similar to those of hawkins and Hoyle. To have an understanding of the 18.61 year cycle, the builders of Stonehenge must have acquired considerable knowledge of astronomy for a period prior to the invention of paper. hawkins noticed in 1964 that if you divide 56 by 3 you get 18.67. Is there a correlation between the number of Aubrey holes and the length of the Lunar cycle ?

Hoyle proposes that the holes were used as a sort of calendar, recording the Sun's and Moon's orbits about the Earth, as if they must have appeared to prehistoric man. For the calendar to work, it must have a starting point. The Sun's cycle would have started about Midsummer's day; although the actual Midsummer rising of the Sun is measured by the heelstone, the importance of determining accurately the very point of Midsummer would mean alignments would have to be measured both before and after this event. This would minimise the risk of missing Midsummer's day due to bad weather or some other reason. At Stonehenge other alignments do exist on the Southerly side of the most Northerly rising point (just South of Midsummer's day position). It appears to Hoyle that the position of the Sun can be accurately determined at least once each year. A marker on the Aubrey holes would be set in its first position on this day. The moon cannot be set in the same as its cycle of 18.61 years would be too long to keep an accurate calendar. If however they realised that when the moon was full it was directly opposite the Sun, the Sun's marker could be used to set the Moon marker. It would be placed 28 holes around from the Sun marker on the first full Moon after Midsummer's day and then checked each following full Moon.

This gives us two markers on the ring of Aubrey holes, one representing the Sun and one representing the Moon. For this calendar to work someone would have to Move the Moon marker anticlockwise two holes each day; this means that a complete circle would be made every 28 days
(just over the actual time time it takes the Moon to orbit the Earth ). The Sun marker would be moved in an anticlockwise direction by one marker every 13 days. This is quite a complicated procedure to keep going just to keep an accurate calendar. If though we introduce the idea that the Aubrey circle representing the ecliptic and add two more markers which represent the nodes at which the Moon crosses the Ecliptic, then the circle could become a more powerful eclipse prediction procedure.

In order to set the two new markers, for simplicity called N and N', the month in which the Moon reaches its most Northerly point of rising in its 18 year cycle must be determined. I have already shown by my own investigations and those of Hawkins and Hoyle that this point can be determined. The slow movement of the Moon about this long cycle means that the point can be determined quite accurately at least one week each way of this point. When the point is determined , marker N would be set 14 holes around in a clockwise direction from the first hole in the yearly cycle, i.e. the hole where the Sun marker is placed on Midsummer's day Marker N' would be set 14 holes around in an anticlockwise direction from the first hole. From that point on , the markers N and N' would have to be moved on three times each year in a clockwise direction; they would complete a full circuit of all the holes in 18.67 years when they would be reset. When the Sun, the Moon and the N or N' marker all coincide on the same hole, then a Solar eclipse will occur. When the Sun is on one of the N markers and the Moon is on the other, then a lunar eclipse will appear. By using other markers, month and years ahead can be tested for eclipses; obviously the closer to the settings of the actual markers, the more accurate the predictions.

This is just one theory of the purpose of Stonehenge. There are many problems with this theory. One of the main ones being that the eclipses would rarely have been visible from the Stonehenge area it does however raise questions about the purpose of stonehenge and the time over which it was built.

Solar year	0	1	2	3	4	5	6	7	8	9	10	11	12	13	14	15	16	17	18	19	20
Degrees From North	44.6	48.1	51.2	53.5	57.1	59.4	59.4	59.4	57.1	54.8	51.5	48.4	45.8	43.00	41.3	39.5	39.9	41.3	43.0	45.8	48.8

Table 1.0 The position the Moon rises at its most Northerly point just before Midwinters Day.  The angles are degrees from North. The years are the number of years from 1500BC.  

Map Of Stonehenge.
Showing Circles & Banks
and some alignments.

Sources Of Reference

1. The British Academy.  The Place Of Astronomy In the Ancient World, Oxford University Press, London, 1974.

2. Hawkins Gerald, Stonehenge Decoded, Souvenir Press, London, 1964.

3. Fred Hoyle , from Stonehenge to Modern Cosmology, W.H. Freeman & Company, San Franciso, 1971

4. Gerald S. Hawkins, Stonehenge Decoded, Souvenir Press, London, 1964.

Ordnance Survey, Landranger 184, Salisbury and The Plain.