Stonehenge – Eclipse Predictor?

4 01 2017

Astronomer Prof. Gerald Hawkins wrote two articles for “Nature” in 1963 and 1964 in which he pointed out several new Stonehenge alignments to the Sun and Moon and proposed that the 56 Aubrey Holes could be used to predict eclipses. His subsequent popular book “Stonehenge Decoded” gave the world the idea that the monument was a Neolithic computer.

stonehenge-decoded-and-gh

Archaeologists were horrified at the thought and the leading authority on Stonehenge at the time, one Richard Atkinson, wrote a rebuttal paper in 1966 called “Moonshine on Stonehenge” which heavily criticised Hawkins conclusions. Atkinson considered the builders of Stonehenge to be “howling barbarians” – a statement he later came to regret.

on-stonehenge-and-fhProf. Fred Hoyle followed up Hawkins’ work on the eclipse predictor idea and came up with a relatively simple recipe for moving markers around the 56 Aubrey Holes to keep track of the Sun, Moon and the two points in the sky where their paths cross (the “nodes”). He published this work in two journal articles in 1966 and then in his 1977 popular book “On Stonehenge”.

 

So how does this eclipse predictor theory work and is it possible that the Aubrey Holes were in fact used like this? We’re going to have to get slightly technical, but it’s not too hard to follow.

Hoyle said that you need a marker for the Sun, one for the Moon and two more for the “nodes”, and that these markers are moved around the 56 holes of the Aubrey Hole circle in a particular way.

The Moon goes around the Earth once in about 27.3 days (the “sidereal month”) so if you move your Moon marker two Aubrey Holes per day it’ll go once round the circle in 28 days.

The Sun goes around the entire sky once in about 365.25 days (the “tropical year”), so if you move your Sun marker two holes every 13 days it’ll go once round the circle in 364 days.

The points where the paths of the Sun and Moon appear to cross (the “nodes”) also gradually move around the sky, taking 18.61 years to make one revolution. This period is called “the regression of the lunar nodes” and occurs because the Moon’s orbital ellipse actually rotates slowly around the Earth.

The Moon’s orbit is also tilted by about 5° to the path of the Sun in the sky, which is why we don’t get eclipses every New and Full Moon – we only get eclipses when both the Sun and Moon are at or very near the “nodes”.

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The node markers are always kept opposite each other – there’s the “ascending node” and the “descending node” – one for each of the two crossing points on opposite sides of the sky.

To keep track of the nodes, you move their markers 3 holes each year – in the other direction to the movement of the Sun and Moon markers. This means the node markers go backwards round the circle once in 18.66 years.

To summarise:

Arbitrary Position and Explanation.png

Now, 28 isn’t 27.3, 364 isn’t 365.25 and 18.66 isn’t 18.61 but the inaccuracies can be corrected.

Every month you can fix the Moon marker by making sure it’s in the Aubrey Hole directly opposite the Sun at Full Moon.

Twice a year, at the solstices, you can make sure that the Sun marker is in the Aubrey Hole closest to Stonehenge’s main axis – either the Aubrey Hole towards the Heel Stone at summer solstice or the one directly opposite it across the circle at winter solstice. The error between 18.66 and 18.61 is actually small enough not to matter.

Suppose you see a lunar eclipse one night, this allows you to set up the markers in the first place. The Sun and Moon markers are placed directly opposite each other (because lunar eclipses are only possible at Full Moon) and the node markers are placed one each in the same holes as the Sun and Moon markers.

Now you follow the recipe for moving the markers, day by day.

If you ever end up with the Sun and Moon markers in the same hole together, and they’re in the same hole as (or in the hole next to) a node marker then this predicts a solar eclipse. Sun and Moon markers in the same hole means New Moon, and solar eclipses are only possible then.

The following animation shows how this works, starting with the solar eclipse of March 20th 2015 and predicting the subsequent lunar eclipse of 4th April 2015.

ah-animation

If all this seems very unlikely and complicated to manage, then you may be right. Hawkins’ and Hoyle’s theories simply show how a 56 hole machine with four markers could be used to track the things that allow you to know when to expect an eclipse to occur.

One of Atkinson’s objections was that if 56 was a useful number for eclipse prediction in the ancient world then it’d be found all over the place – not just at Stonehenge. What’s more, up until the 1960s the number 56 wasn’t associated with eclipse cycles by astronomers.

Curiously, it was discovered later that perhaps the ancients did link 56 with eclipses. There is a passage in Plutarch’s “Of Isis and Osiris”, dating to the 2nd Century AD, which says:

“The Pythagoreans also clearly believe Typhon to be a daemonic power… the 56-sided polygon is said to belong to Typhon, as Eudoxus [Greek astronomer c.370 BC] has reported…

There are some who give the name Typhon to the shadow of the earth, into which they believe the moon falls and so suffers eclipse…”

The argument continues even 50 years on – the builders of Stonehenge clearly weren’t “howling barbarians” and the builders of that monument and others definitely paid attention to the sky and how things moved around it.

Humans have been curious for as long as we’ve been humans and the earliest artifact that has a record of the phases of the Moon on it is a carved bone from the central European Aurignacian culture which is about 32,000 years old (https://sservi.nasa.gov/articles/oldest-lunar-calendars/)

Perhaps we’re still underestimating our ancestors’ abilities, despite the evidence they’ve left behind.

Article by guest blogger and local Stonehenge historian Simon Banton

Stonehenge guided tours are considered the leading Stonehenge experts and offer a range of guided tours including Full Moon and Eclipse Tours, many taking you into the inner circle at sunrise or sunset. Private Stonehenge tours with a Stonehenge expert and astronomer can easily be arranged.

If you want to here more about Stonehenge and the astronomical calendar you could join a Stonehenge walking tour with a local Archaeoastronomer who offers amongst guided walks, talks and even full moon tours.

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Friday will see a rare cosmic coincidence. Was Stonehenge used to predict eclipses?

19 03 2015

As the eclipse plunges Wiltshire and other places into darkness this Friday (March 20th), two other rare if less spectacular celestial events will be taking place, too: the Spring equinox and a Supermoon. Friday will see three rare celestial events and this will be the first time in living memory that the Spring equinox, a solar eclipse, and a supermoon are all taking place on the same day in the UK.

One of the most intriguing mysteries in the world is the Stonehenge. Nobody knows who built the mysterious Stone Circle in Wiltshire, or what its purpose was exactly. There are many theories associated with Stonehenge and archaeologists have been debating for ages to determine why it was built. Most experts believe that Stonehenge is actually an ancient astronomical calculator.

Eclipses have long been feared as bad omens, but the equinox is celebrated as a time of renewal

Eclipses have long been feared as bad omens, but the equinox is celebrated as a time of renewal

Eclipse Cycles

Now, it’s widely accepted that Stonehenge was used to predict eclipses. The inner “horseshoe” of 19 stones at the very heart of Stonehenge actually acted as a long-term calculator that could predict lunar eclipses. 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. Moving this marker one lunar month at a time – as opposed to one lunar day the others were moved – 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.

Aubrey Holes
Stonehenge has a ring of 56 pits that are now known as Aubrey holes, after antiquarian John Aubrey. They date back to the late fourth and early fifth millennium. These holes were not really noticed until the 1920s. It’s believed that the only standing feature at Stonehenge at the time these holes were dug was the Heel Stone – the marker of the midsummer sunrise – but this is now proven false. Some experts believe they were meant to hold timbers or more stones, but the astronomical interpretations of these holes are very interesting. It’s also believed that the holes helped to predict astronomical events. Complicated math theories back this up to some degree, as some lunar eclipses can be predicted by using numbers associated with Stonehenge. It’s even believed that Stonehenge was used to keep track of lunar cycles by moving marker stones two holes per day, ending with 56 holes.

Hawkins
Meanwhile, Gerald Hawkins studied Stonehenge much later, in 1965, using computer programs. He found multiple solar and lunar alignments that correlated with the location

of Stonehenge. He set his data so that the positions of the stars and planets would match where they were in 1500 B.C., when he believed it was built, and found that 13 solar correlations and 11 lunar correlations matched up with the megalithic stages. In other words, he believed Stonehenge was used to predict astronomical events. He also believed that it was built to align with the position of the summer and winter solstices.

What is a solar eclipse?
A solar eclipse happens when the moon passes between the sun and the earth, hiding the sun from view and blocking out the sunlight that usually reaches us.

The eclipse, which will be partial, not total, will begin here at around 8.45am on Friday and peak at around 9.30am before ending at 10.30am. It will be the biggest eclipse since August 1999.

Spring equinox

The equinox will also happen on March 20th. While it won’t have any discernable, direct impact on how the solar eclipse looks, it will contribute to a rare collision of three unusual celestial events.

On March 20th, the Earth’s axis will be perpindecular to the sun’s rays — which only happens twice a year, at the two equinoxes. After that, it will start tipping over, making the days longer in the northern hemisphere.

As such, the equinox has long been celebrated as a time of beginning and renewal, by a number of historic cultures, and is linked to Easter and Passover.

The equinox will happen at the same time as a solar eclipse in 2053 and 2072, though it doesn’t always appear as close together as that.

English Heritage will welcome people to Stonehenge to celebrate the Spring (Vernal) Equinox on Saturday 21st March. Expect a short period of access, from first light (approximately 05:45am) until 08:30am. Click here for more info

Supermoon

A very rare supermoon eclipse of the sun is happening this week that won’t take place again until 2034.  A supermoon is when a full, or new moon coincides with the night when the earth and moon’s orbits move them slightly closer together, making the moon look about 14% bigger, and 30% brighter than normal. This generally happens roughly once every 14 months, but can happen more often; in January 2014, there were actually two supermoons in a single month.

In the past, groups have argued that the supermoon could cause natural disasters, madness, or even throw the earth off its axis. Experts agree that the worst thing that might happen is the tide comes in another inch that night.  As well as a supermoon, there is also an event when a full moon is as far away from earth as possible; this is called a micromoon, for obvious reasons.

Some useful Links:

Solar eclipse, Supermoon, Spring equinox:

Solar Eclipse, Supermoon, Spring Equinox: 3 Rare Celestial Events Align March 20th

Solar Eclipse 2015: How to watch a solar eclipse safely

Stonehenge: An Astronomical Calculator

Astro-Archaeology at Stonehenge

Remember that no one should look directly at the sun during a partial eclipse without proper equipment, as it can damage the eyes.

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