As Fall Equinox Approaches, Was Stonehenge Used to Predict Astronomical Events?

The sun sets behind Stonehenge, in Wiltshire, England, in 2010. Kieran Doherty/File Photo/Reuters

This Friday night and Saturday morning, druids, pagans, hippies, and assorted hangers-on will gather at Britain's world-famous neolithic "Stonehenge" site to mark the fall equinox, the point when summer ends and the days begin to shorten.

But what will they be celebrating and what even is Stonehenge for, anyway? Here's what you need to know.

The fall equinox

"This is the third of the four 'sky points' in our Wheel of the Year and it is when the sun does a perfect balancing act in the heavens," says a piece on the Stonehenge blog. "After this celebration the descent into winter brings hours of increasing darkness and chiller temperatures. It is the time of the year when night conquers day."

According to the blog, in rural Britain, including in Wiltshire where Stonehenge is located, it was traditional to drink Dandelion and Burdock—a class British soft drink—to "cleanse the blood" and provide "a good tonic for the body."

The nearest full moon to the equinox is known as the "harvest moon." Farmers would celebrate it as the end of the second harvest. Livestock would then be salted and preserved at the equinox to provide food for the winter.

The pagan term for the celebration is Mabon. During medieval times, like all pagan festivals the occasion was Christianized by the Church, who called it Michaelmas, the feast of St Michael.

Stonehenge was first associated with druids by Early Modern writers amid a resurgence of ancient Pagan culture in England, and many neo-druid orders have held ceremonies there since the early 20th century.

The significance of Stonehenge

Nobody knows for sure what the purpose of the stone circle at the Stonehenge site was.

"With a history spanning 4,500 years Stonehenge has many different meanings to people today. It is a wonder of the world," says the site's page on the English Heritage website, "a spiritual place and a source of inspiration."

The circle as it is seen today was erected in about 2,500 BC. It comprises two types of stones; larger "bluestones" and smaller "sarsens."

According to English Heritage, "the interpretation of Stonehenge which is most generally accepted is that of a prehistoric temple aligned with the movements of the sun."

It could have functioned as a calculator for predicting lunar eclipses, many believe: "By moving one of Stonehenge's markers along the 30 markers of the outer circle, it's discovered that the cycle of the moon can be predicted," the Stonehenge blog says.

"Moving this marker one lunar month at a time... made it possible for them to mark when a lunar eclipse was going to occur in the typical 47-month lunar eclipse cycle."

"The marker would go around the circle 38 times and halfway through its next circle, on the 47th full moon, a lunar eclipse would occur."

But that's far from the only theory that's been put forward. According to English Heritage: "It has also perhaps been the focus of more theories about its origin and purpose than any other prehistoric monument."

"These have included a coronation place for Danish kings, a Druid temple, a place where ancestors were worshipped or a cult centre for healing."