One of the world's most famous ancient astronomical sites is Stonehenge. This complex prehistoric assembly of boulders and ditches is located in the southwest of England, about 8 miles (13 kilometers) from the town of Salisbury. In September 2008, English archaeologists announce results from radiocarbon testing of organic matter buried under Stonehenge, that date the construction of the circle of stones located on the Salisbury Plain to approximately 2300 BC--a date almost three hundred years later than prior scholarly estimates of the date of the construction of Stonehenge. Analysis of the giant stones indicates they were taken from a site in Wales and transported nearly 150 miles (240 km) to the present site of Stonehenge. Scholars continue to differ on explanations regarding the purpose and use of Stonehenge.
Construction of Stonehenge took about 30 million worker hours of labor.
The architects of this monument were probably ancient druids, an order of Welsh and British priests. While Stonehenge is widely believed to have had some astronomical or religious function, exactly what that function was remains in question.
Effects of about 5,000 years of rain and wind, plus the action of vandals, have significantly altered Stonehenge from its original form. Studies undertaken by archaeologists and anthropologists indicate that at one time it contained thirty blocks of gray sandstone, each standing about 13.5 feet (4.1 meters) high, arranged in a 97-foot-diameter (29-meter-diameter) circle. Lying horizontally on top of these stones and forming a continuous ring were thirty smaller stone slabs. A second inner circle of stones enclosed a third horseshoe-shaped group of stones. Today, all that remains is a partial outer ring and a handful of inner stones.
The most popular theory about the astronomical function of Stonehenge is that it was a calendar marking the summer solstice,; a solstice is the two points on the Earth's orbit about the Sun when its axis tilts the most either toward or away from the Sun. According to this theory, the solstice can be observed by standing at the center of the ring of stones and looking toward the northeast. There, beyond the stones, framed by three segments of the circle (four upright stones topped by three horizontal stones) is a pillar called the Heel Stone. The top of the Heel Stone, which appears to line up with the distant horizon, is very close to the spot where the Sun's first rays strike on the summer solstice.
This design, however, is not precise. The Sun rises slightly to the north of the Heel Stone, raising questions about the validity of the theory. Some historians argue that the degree of error is not significant and that the ancient builders just did not hold themselves to the exact standards held today. Others contend that it is merely coincidental that on the solstice the Sun rises at a point near the Heel Stone, and that the Heel Stone either served some other function or none at all. The answer to this question and others may lay beneath the nearly one-half of Stonehenge that has not yet been excavated.
Construction of Stonehenge
In the 1920s and 1950s, partial excavations revealed some of the history of the construction of Stonehenge. It seems most likely that the first stage of Stonehenge, which was built around 3,100 bce, consisted only of a circular ditch surrounded by an embankment, plus an inner circle of fifty-six pits. Several tall stones marking the entrance and the Heel Stone were probably also erected at this time.
The next phase of construction came in about 2,150 bce, with the erection of two concentric circles of stones in the center of the monument. Then, around 1,550 bce, a third group of stones was arranged in a horseshoe shape within the inner circle. The final stage--the addition of a long avenue leading up to the monument--probably took place around 1,100 bce.
In addition to the solstice-marker idea, many theories have been proposed as to the astronomical significance of the alignment of particular groups of stones. For instance, there are over fifty sets of stones that are thought to have been lined up with the Sun and the Moon at various times of year. Too many unknowns remain, however, to determine which of these theories is true. Perhaps if the rest of the site is excavated in the future, more answers will be forthcoming.
In 1915, Stonehenge was purchased by English rancher Cecil Chubb (1876-1934). He donated it to England in 1918. Today Stonehenge is a popular tourist attraction. Stonehenge itself is owned and managed by the group English Heritage, while the land surrounding it is owned by the National Trust. As a result of vandalism, however, the inner circle of stones has been closed off to the public by a fence topped with barbed wire. The only group to gain access to the inner circle is a modern-day order of white-robed druids who perform the same rituals on the summer solstice they claim have been performed by druids over the millennia.