Across Western Europe are collections of standing stones dating back thousands of years that scientists have long suspected were huge astronomical computers, but that's largely been a matter of conjecture. Now a team of scientists from the University of Adelaide has statistically proven that some of the oldest standing stones in Britain were deliberately constructed to align with solar and lunar movements.

Built over 5,000 years ago during the Late Neolithic and early Bronze Ages, the standing stones of Europe range from small, isolated circles in the Scottish Isles measuring only nine meters (30 ft) across to huge complexes 450 m (1,500 ft) wide set in huge ceremonial parks.

The most famous of these is Stonehenge in Wiltshire, which was begun before the pyramids of Egypt and took over 2,000 years and 1.5 million mandays to build using giant megaliths floated on barges and dragged overland from Wales. Why it was built has long been a matter of speculation that has included the idea that it was a temple built by the Druids for human sacrifices, a war memorial erected by King Arthur, or a monument to the ancient British queen Boudica.

One clue to why Stonehenge and the many other stone circles were constructed is the fact they exhibit alignments with the Sun and the Moon and various astronomical events, such as sunrise on the summer solstice, sunset on the winter solstice, the movements of the Moon during the 18.6 year Metonic cycle, and solar and lunar eclipses

This has been noticed since the 18th century and sparked the field of modern archaeoastronomy after scientists applied computers to standing stones in the 1960s. This gave rise to the idea that the stones are themselves primitive computers as well as ancient observatories.

The problem is that though modern computers had no trouble showing that standing stones could have astronomical alignments, they couldn't prove that such alignments weren't just coincidental. For example, Salisbury Cathedral, which is less than 20 mi (32 km) from Stonehenge, is loaded with all sorts of astronomical alignments, but those are all because it's built to face east. They are purely accidental.

"Nobody before this has ever statistically determined that a single stone circle was constructed with astronomical phenomena in mind – it was all supposition," says project leader and University of Adelaide Visiting Research Fellow, Dr Gail Higginbottom.

The Standing Stones of Stenness were built over 5,000 years ago(Credit: University of Adelaide)

To fill this gap, the Adelaide team studied the Callanish stones on the Isle of Lewis in Scotland and the Stenness stones on the Isle of Orkney, which were both 500 years older than the oldest stones of Stonehenge. Using statistical analysis of two-dimensional and three-dimensional alignments, the Adelaide team found that the stones showed a concentration of solar and lunar alignments, and that simpler stone circles built in Scotland 2,000 years later showed the same alignments.

In addition, the analysis revealed that these alignments not only included the stones, but the surrounding landscape and horizon as well. This showed that the ancient Britons connected the Earth to the sky in designing their stone circles, and that they continued this practice for two millennia. Also, the pattern of alignments was reversed in half the sites.

"These chosen surroundings would have influenced the way the Sun and Moon were seen, particularly in the timing of their rising and setting at special times, like when the Moon appears at its most northerly position on the horizon, which only happens every 18.6 years," says Higginbottom. "For example, at 50 percent of the sites, the northern horizon is relatively higher and closer than the southern and the summer solstice Sun rises out of the highest peak in the north. At the other 50 percent of sites, the southern horizon is higher and closer than the northern, with the winter solstice Sun rising out of these highest horizons.

"These people chose to erect these great stones very precisely within the landscape and in relation to the astronomy they knew. They invested a tremendous amount of effort and work to do so. It tells us about their strong connection with their environment, and how important it must have been to them, for their culture and for their culture's survival."

The team's research was published in the Journal of Archaeological Science Reports.

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