(A) Lunar Nodes

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 29.5. 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.

This diagram shows the moon and sun's apparent motion about the Earth. Lunar eclipses occur when the sun is in one node and the moon at the other. This allignment can only occur during a full moon.  

These two invisible points in space are called the lunar nodes. They are the points where the Moon's orbit, which is tilted slightly, 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.



(B) Using the Aubrey Holes ( Solar & Lunar Eclipses )

Method 1

The actual motions of the Sun and the Moon are reflected in the structure of Stonehenge, and it may have been used to keep track of these cycles. The number of stones or holes ( EG. the Aubrey 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.

How is Stonehenge useful in PREDICTION??

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. 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.


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, 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.


Method 2

Anyone who has ever tried to make a model of how the Sun and Moon move around the Zodiac will end up, most simply, with a circle of 28 markers around a central earth. Moving a 'Moon-marker' one position per day and a 'Sun-marker' once every 13 days provides a calendar accurate to 98%. (Figure 3.3)


Every year, for about 34 days, the full and new moons occur near the Sun's path (the ecliptic) and eclipses result. These two times, which are 173 days apart, move backwards around the calendar taking 18.6 years to complete a revolution. The precise two points where the moon crosses the apparent path of the sun through the zodiac (the ecliptic) are the lunar nodes, as mentioned above.

By doubling the sun-moon calendar to 56 markers, we can obtain an accuracy of 99.8%, and meet the handy convenience that 18.6 x 3 is almost the same as 28 x 2. Now a 3:2 ratio enables eclipses to be predicted to high accuracy, as the picture shows. (Figure 3.6)


The 'Aubrey Calendar' has predicted lunar and solar eclipses accurately to the day, shown instantly the position of the sun and moon against the stars, indicated lunar phase at a glance and, with a 24-hour clock placed in the centre, enabled the state of the tides to be known. The link between this theory and the Aubrey circle is that the Aubrey circle had 56 stones.


(C) Using the Bluestone Horseshoe ( Lunar Eclipses )


The Bluestone Horseshoe, consisting of 19 upright columns at the monument’s center, could predict successive lunar eclipses. This was done by placing a stone marker on top of a pillar at one end of the horseshoe during a lunar eclipse, and moving it to the adjacent pillar every full moon.

Moving the rock this way every lunar month, the marker would stand at the center of the horseshoe after two-and-a-half trips around the row – 47 months after the original eclipse. The full moon that rose that month would fall into Earth’s shadow during the night. That stone could then be taken down and moved to the beginning of the horseshoe again.

It predicts all lunar eclipses occurring at Stonehenge without predicting a lot of eclipses that wouldn’t be visible from the site.

Stonehenge builders could have kept track of lunar eclipses by moving rocks around the monuments inner curve of 19 columns called the Bluestone Horseshoe. Placing a rock on top of one of the horseshoe’s outermost columns during an eclipse and moving it over one column every full moon, the marker would stand atop the center column during a full moon 47 months later, a moon that would be eclipsed.

The trick that complicates this explanation, however, is that more than one lunar eclipse would have been visible from Stonehenge every 47 months. The keepers of the stones could have had more than one rock traveling around the Bluestone Horseshoe at once, In fact, there may have been as many as six, depending on the frequency of eclipses.

No matter how often eclipses are seen within a 47-month cycle, the eclipses that are separated by 47 months are all related to each other and form a family. A family begins as a partial, or penumbral eclipse and it recurs every 47 months. Each time it would be a little closer to a total eclipse. There might be a dozen or so total eclipses in the family, and then the eclipses would grow more partial, eclipsing a smaller part of the moon every 47 months until the eclipse failed to appear. That family would then be finished, and the stone that marked it could be retired.