The following material was adapted from ECLIPSE by Bryan Brewer

Every year on the first day of summer, the Sun rises at a point that is farther north than on any other day of the year. At the ruins of Stonehenge in England, this solstice sunrise appears on the horizon in direct alignment with the massive heel stone. This is the most outstanding feature of this ancient monument, built during the same era as the Great Pyramid of Egypt. There is little doubt that the builders of Stonehenge used it to mark this special day as the beginning of each year. By counting the number of days between these annual alignments, they could determine the length of the year. This could serve as a practical calendar to mark holidays and seasonal festivals and to ensure the timely planting and harvesting of crops.

But to predict eclipses, knowledge of two other cycles is required. One of these -- the length of the lunar month -- is easily determined. It is simply the number of days between one full Moon and the next. This cycle of 29-1/2 days is marked at Stonehenge by two rings of 29 and 30 holes, which together average 29-1/2. The other cycle, however, is of an altogether different character: it is a cycle of rotation of two invisible points in space. The evidence shows that the builders of Stonehenge probably discovered this cycle and could have used it to predict eclipses.

These two invisible points in space are called the lunar nodes (from the Latin for "knot"). They are the points where the Moon's orbit, which is tilted at a slight angle, intersects the plane of the Earth's orbit. It would have taken many decades of watching countless risings and settings of the Moon to figure out the cycle of the lunar nodes. This information -- which must have been passed on from generation to generation -- is preserved at Stonehenge. All the Moon alignments necessary for determining this cycle are marked by massive stones.

Who were these people who observed this subtle cycle even before the first metal tools were used by humankind? Some have suggested that Stonehenge was built by Druids, but we don't really know much about the builders. We do know that the actual motions of the Sun and the Moon are reflected in the structure of Stonehenge, and we can reason how it may have been used to keep track of these cycles. The number of stones or holes in the ground in the various rings around Stonehenge each represents a certain number of days or years in the cycles. By moving markers (such as stones) around a ring in time with the cycles, the positions of the Sun and Moon -- and the two invisible points -- can be tracked. (The details of this method are explained in Chapter 2 of the book ECLIPSE, by Bryan Brewer.)

An eclipse can occur only when the Sun is close to being aligned with a node. By using Stonehenge to keep track of the position of the Sun and the nodes, these "danger periods" for eclipses can be predicted. A new (or full) Moon appearing during one of these periods would call for a special vigil to see if the solar (or lunar) eclipse would be visible from Stonehenge. A total solar eclipse would be a rarity. But the law of averages confirms that either a partial solar eclipse or a lunar eclipse can be seen (weather permitting) from the same point on the Earth about once every year.

Why would eclipses have been so important to the ancient people of Stonehenge? Perhaps they considered the darkening of the Sun or the Moon a fearsome event -- a celestial omen of doom or disaster. Many cultures have interpreted eclipses this way. But the sophistication of the astronomy of Stonehenge suggests that the builders had something different in mind. Their understanding of the solar and lunar cycles must have led to a high regard for the cosmic order. Eclipses may have been seen as affirmations of the regularity of these cycles. Or perhaps the unseen lunar nodes formed an element of their religion as invisible gods capable of eclipsing the brightest objects in the heavens.

The idea that Stonehenge may have been a center for some kind of worship has occurred to many. It is not hard to imagine Stone Age people gathering at a "sacred place" at "sacred times" (such as solstices, equinoxes, and eclipses) to reaffirm their religious beliefs through ritual practices. British antiquarian Dr. William Stukeley, who in 1740 was the first to note the summer solstice alignment at Stonehenge, advanced the notion that the monument was built by Druids to worship the serpent. He claimed that Stonehenge and similar stone circles had been serpent temples, which he called "Dracontia." Could this serpent symbolism be related to eclipses? Recall that the key to eclipses is the position of the lunar nodes. The length of time for the Moon to return to a node (about 27.2 days) astronomers call the draconic month. (Draco is the Latin word for "serpent" or "dragon.) Perhaps the mythical serpents of Stonehenge and the legendary dragon that eats the Sun are symbols of the same thing: the invisible presence in time and space that eclipses the Sun and the Moon.

Who built Stonehenge? How? Why?

This ancient monument of huge stones solitarily standing on the Salisbury Plain in Wiltshire, England has captured imaginations for centuries. Theories about who built it have included the Druids, Greeks, Phoenicians, and Atlanteans. Speculation on the reason it was built range from human sacrifice to astronomy.

Investigations over the last 100 years have revealed that Stonehenge was built in several stages from 2800 - 1800 BC. It seems to have been designed to allow for observation of astronomical phenomena - summer and winter solstices, eclipses, and more.

Where in the world is Stonehenge?

England

Mystery of Stonehenge points to the heavens

By Sandra Dimitrakopoulos, April 15, 2004

Stonehenge itself remains a steadfast observer of the world, watching the seasons change from summer to fall to winter to spring and back again thousands of times over. But it also bears witness to movements in the heavens, observing the rhythm of the Moon and, more noticeably, the Sun.

For most parts of the year, the sunrise can't even be seen from the centre of the monument. But on the longest day of the year, the June 21st summer solstice, the rising sun appears behind one of the main stones, creating the illusion that it is balancing on the stone.

This stone, called the "Heel Stone", sits along a wide laneway, known as the Avenue, that extends from the northeast corner of the main monument. The rising Sun creeps up the length of the rock, creating a shadow that extends deep into the heart of five pairs of sarsen stone trilithons -- two pillar stones with one laid across the top -- in the shape of a horseshoe that opens up towards the rising sun.

Just as the Sun clears the horizon, it appears to hover momentarily on the tip of the Heel Stone. A few days later, on midsummer's day, the sun will appear once again, but this time, it will begin to move to the right of the heel stone. The same phenomenon happens again during the winter solstice, only it's in the opposite direction and a sunset. But both indicate a change of season.

But who would have needed to make this connection between Earth and Sun. The first builders, who may have just started farming the land, might have needed to know when the seasons were about to change. At a later phase in its development, Stonehenge may have been used as some sort of temple, or it could have been an astronomer's tool, used to judge the movements in the heavens.

"Nobody really knows at all what [Stonehenge] was intended for," says Christopher Witcombe, a professor of art history at Sweet Brian College in Virginia and an authority on Stonehenge.

"The fact that it was built over a long period of time makes it difficult to know if it maintained the same function over the time period or not."

But this doesn't mean there aren't a number of theories that set out to explain Stonehenge's purpose. Eighteenth century British antiquarian, William Stukeley, was one of the first people to report seeing the event of the sunrise on that special day in June. This led him to believe that Stonehenge was a temple, possibly an ancient cult centre for the Druids. Although this theory isn't as popular now, the religious aspect attributed to Stonehenge has influenced how it has come to be understood, even today.

"When people started paying attention to Stonehenge, back in the 18th century, people like William Stukeley were calling it a temple," says Witcombe. "That sort of association has been more or less attached to Stonehenge for the last two or three hundred years."

Others, like 20th century British astronomer, Sir Norman Lockyer,also saw Stonehenge as a temple, but a temple to the Sun. For him, its significance lay in elebrations of ancient Celtic festivals.

But to see Stonehenge as a temple, or retaining a religious quality may just be an assumption. It is a structure that clearly does not resemble a house or hall or anything else secular, which could indicate that it is sacred, according to Witcombe.

"We're also influenced by the fact that a lot of the more complex buildings that survive from the ancient past, like in Greece and Egypt, are buildings that are religious," says Witcombe. "We are presuming that's also the case with Stonehenge."

There are also more than 400 burial mounds surrounding the ancient monument. Many of these graves have been found to contain gold breast plates and other precious metal items. These people may have wanted to be buried close to Stonehenge, which could reinforce a spiritual aspect, or as modern day astronomer Gerald Hawkins says in his book, Beyond Stonehenge, a concern for life after death.

In the middle of the 20th century, a new theory was born -- one that suggests that Stonehenge could have been used as an astronomical calendar, marking lunar and solar alignments. If this is true, it would have held great power for the people who controlled the megalithic monument.

"Astronomers, just because of what they were able to do, must have seemed, to the ignorant, something esoteric and mystical," says Witcombe.

Aside from the sarsen horseshoe trilithons that open in the direction of the sunrise, there are four stones, called "Station Stones" that may have played an astronomical role. These were placed in a rectangle around the main monument, within the ditch and bank that surrounds the circle of stones. These are believed to point out the moonrise, moonset, sunrise and sunset. Only two stand today.

One of the first people to propose the idea that Stonehenge could have been a tool used in understanding the heavens was 20th century astronomer Gerald Hawkins. He proposed that Stonehenge, which he called a primitive astronomical computer, could predict events of the Moon and Sun as well as eclipses. Hawkins discovered astronomical patterns in the station stones, possibly erected in the first phase of building, and within gaps between trilithons set up the last phase of building. This connection was made by computer calculation, based on maps and charts. It led him to believe that because astronomical properties could be found in two aspects of the monument, there is definite evidence of a heavenly purpose.

Modern day astronomer, Fred Hoyle, tested Hawkins hypothesis. "I set myself the clearcut target of finding out if the stones that exist at Stonehenge could, in fact, be used to predict eclipses -- and it seemed to me that they could."

56 Aubrey holes shown here were
believed to be a tool of the heavens.

Hoyle took a slightly different approach to Hawkins. His calculations are based on the 56 pits or "Aubrey Holes" first discovered in the 17th century by British antiquary John Aubrey. These holes can be found on the inside circle created by the ditch and bank, or henge. Hoyle believed it was possible to determine eclipses by moving three markers, or stones, around the Aubrey holes in such a way that when all three arrived at the same hole, an eclipse of the Sun or Moon was about to occur.

But Stonehenge may not have always been used in this way, according to Hoyle. He believes that the first phase of building, where it was simply a ditch and bank with 56 pits (the Aubrey holes) carved out on the inner side of the henge, is the only section of Stonehenge that holds astronomical value.

"I was convinced that the inner part, which was built around 1500 BCE, was really mostly a matter of simply religious construction," Hoyle says. "I thought the people who built the first structures there, approaching 3000 BCE, were the cleverest and that the later people didn't know what they were doing."

And there may be many more theories that haven't even been explored or discovered yet. One just proposed suggests that Stonehenge is a sexually symbolic site, with both male and female represented in stone.

"In some cases, some of these ideas may initially sound a bit wacky, but you never know -- there may be one or two aspects of them which may indeed have some bearing," says Witcombe.

Although the purpose of the stone monument is still unsure, most people think its worth preserving, for one reason or another.