Newgrange (right) and Knowth (far left, behind trees) and the Boyne in flood.

The Boyne Valley passage mounds attract worldwide attention and undoubtedly deserve World Heritage Site status. Until now, the archaeologist's viewpoint has been dominant - that they are primarily burial mounds. Gillies Macbain argues that a wider perspective is needed, to include astronomy and other sciences. His astronomical and mathematical arguments presented here offer compelling evidence that these mounds were built to act as calanders based on the movements of the sun, moon and the star Venus.

When I first wrote down my conclusions on the passage mounds – I sent a copy to Professor Eogan, an archaeologist, and another to Professor Wayman, an astronomer. The distinguished archaeologist wrote back saying " I can't comment on your theories because I am not an astronomer". The distinguished astronomer wrote back saying that the numbers looked right but he couldn't comment on them because he was not an archaeologist!

I have to acknowledge my debt to the expert authors and authorities – but I don't believe that archaeology itself is enough: To get the full picture you need archaeology but also anthropology, astronomy, agriculture, architecture, ancient history, mythology and the history of religion – and a dash of common sense.

Surely Newgrange has to be more than a grave? There are a number of ways of burying a body easier than under 200,000 tonnes of stones. Let the archaeologists call it a passage grave. I prefer to call it a passage mound. It is permissible to see this complex of mounds as the longest and greatest engineering project ever undertaken on this island of Ireland.

If you want a better word to describe the three great mounds in the Boyne Valley, then I suggest the word "cathedrals" would be the most appropriate.*

Regarding the sun, the moon, and the calendar. From my own house in Tipperary the sun sets behind the Devil's Bit mountain: The Gap of Barnane. On the 15th August each year, if the weather is clear, the sun is seen to set exactly in the Bit. That is the Feast of the Assumption and the cathedral in Thurles is the Cathedral of the Assumption. The 15th of August is also the date of Nenagh show and the meaning of "Nenagh" is "annual" or "annual fair".

Now here is another curious thing: If the sun goes down exactly in the Devil's Bit on the 15th August, just eight weeks after midsummer, it must do the same trick on its way north along the horizon eight weeks before midsummer. It will also rise, on the 14th February, just eight weeks after midwinter on the exactly opposite point of the horizon.

And what is opposite the rising sun? As the sun rises, the full moon sets, and once every 19 years this full moon will coincide with the 14th February and also set directly in the Devil's Bit.

The moon's behaviour has complications which would take too long to explain, but you can take it that a front door accidently lined up with the sun, can equally certainly be said to be lined up with a regular setting or rising of the moon.

Would anyone build a passage mound with a deliberate alignment on a phase of the moon which occurred only once in 19 years? The answer is that neolithic man, yes, would. It is only us in our headlong age with our illusion of constant progress, who think in the short-term.

THE 19-YEAR CYCLE

Let me explain this 19-year thing: The problem of the calendar makers is to reconcile the apparent motion of the sun and moon. Seen from the earth, the sun goes around every 24 hours. The seasons are caused by the tilt of the earth in its orbit, and this orbit takes 365.25 days. We know this fact so well that we tend to forget that the length of the year is completely unrelated to the length of the day. As for month, the word comes from the word "moon". The moon in fact goes around anti-clockwise – only the spin of the earth makes it look clockwise. The month lasts 29.5 days from new moon to new moon. The year is twelve moon months and 10.9 days left over. So some years have thirteen new moons.

By a pure coincidence of the solar system, 19 sun years are almost exactly equal to 235 moon months. So if the moon and the sun are in a particular configuration on a particular day of the year, they will be in the same configuration with the moon at the same phase, on the same day, 19 years later. This 19 year cycle is an astronomical one, but it is used in the Christian calendar to determine the day on which Easter occurs.

None of this information is original or new. What is new is that we are bringing together information from one field to throw light on another.

DOWTH AND KNOWTH

Let us now deal with Dowth and Knowth – the other two major passage mounds on the Boyne. Dowth was traditionally held to have been built by the druid Bres and means "darkness" in Irish. The story is that darkness fell upon the earth before the mound was completed. I take this to mean an eclipse. Dowth has 115 kerb stones. If you go around twice that makes 115 x 2, or 230 stones. 230 is the number of moons (new moon to new moon) in the 18.6 year cycle, after which the pattern of eclipses repeats itself. Dowth faces in a westerly direction. The west is where you see the new moon, and the new moon, OR dark moon, is the time when eclipses of the sun occur: It all fits.

The reference to a 19-year cycle would be very appropriate for Knowth, which has passages facing east and west. At the equinox the sun comes up due east in any part of the world, and sets due west. Once every nineteen years the moon will be full on the same day as the equinox. Likewise half way around the cycle, after 9.5 years,the new moon will do the same at the autumn equinox, but with, not opposite, the sun. The eastern passage may also be slanted slightly south of east, towards the old moon preceding the equinox.

Let me explain: To see the old moon, you look east – it rises before the sun, a little closer every day until it disappears in the glow of dawn. Similarly, to see the new moon you look west. It sets a little later than the sun, every day. So the old moon at Knowth would give about 3 days warning of the new. Knowth has 127 stones and 127 is half of 254 – the number of sidereal moons in 19 years. Sidereal means coming back to the same point in the stars. That takes the moon 27.3 days. Meanwhile the sun has moved on in the annual circuit and not until 29.5 days does the moon catch up.

So the number of kerb stones at Knowth is either one of the greatest coincidences of all time or it indicates beyond doubt a detailed knowledge of the moon, and an understanding of the circling of the stars.

Our most difficult task is to get inside the mind of a people who can neither read nor write, but are skilled at designing and building in stone, and so advanced in their observations of the heavens that we find it hard to keep up with them, even now in an age of television and universal education!

Dowth and Knowth yielded their secret fairly easily, now what about Newgrange?

If Dowth is the first mound, watching the 18.6 year cycle of the eclipses – and Knowth is the second, watching the 19 years coincidence of sun and moon, what else is there to track? There is the 8 year cycle of the planet Venus. The planet Venus goes around the sun – as seen from the earth which is also moving – in 584 days. During this cycle it appears once as the morning star, and once as the evening star. By another astronomical coincidence, five of these Venus cycles make nearly the same number of days as there are in eight years, – in fact after eight years Venus comes back ahead of the sun, just 2.5 days early.

Now I want you to imagine a coming together of the winter sun, the new moon, and the planet Venus. The calendar maker has to decide what day to chose for day one. We chose January 1st and anno domini 1 (1 A.D.) as our starting points. But the winter solstice is a natural starting point for the sun; for the moon the new or darkened moon; and for Venus the inferior conjunction when it passes across the face of the sun and can be visible as a black dot under certain conditions.

I am saying that Newgrange may be designed to look out for a day which is day one of the suns year, day one of the moon's nineteen year cycle and day one of the planet Venus' eight year cycle. The lowest common denominator of the one year sun cycle, nineteen year moon coincidence and eight year Venus coincidence is 1 x 19 x 8 = 152. 152 fits Newgrange in the following way: Newgrange has 97 kerb stones. Make the entrance stone K1 and the highly decorated stone K52 represent the days of triple conjunction. There are 95 kerb stones remaining. Each kerb stone = one 584 day cycle of Venus. Thus each five stones = 8 years. Thus the stones make 19 x 8 years or 152 years. This represents a "great year" of sun, moon, and Venus.

To me this is the meaning of the regular phrase in mythology 'three fifties plus two'. It is the sun/ moon/ Venus cycle. The theory that I am putting forward assumes a knowledge of the movements of the sun, moon, and Venus, on the part of the passage mound builders.

So the most conservative archaeologists now accept the alignment of Newgrange with the midwinter sun. All of the circumstantial evidence points to an association of the Boyne valley with the moon after which it is named (Boyne = cow. The moon was known as the white cow). And the third person of this neolithic trinity is the planet Venus.

At Newgrange the folk tradition of county Meath was that the morning star (Venus) shone into Newgrange once in every eight years. It takes Venus five cycles, as we saw, to come back into line with the solar year. That is why Venus is represented as a five pointed star. Of course, what we are celebrating is not just any old star, but the morning star which announces the dawn.

A fundamental problem of religion is to reconcile the natural, unconscious, night-time mind, with the rational, conscious, daylight mind. The morning star which brings the dawn is the messenger of love, reconciliation, and the coming of the light. It is a parable of nature. The star of Bethlehem is a lot more than a children's story. It stands for the meeting point of day and night, of reason and feeling, the reconciliation of man with creation and the reconciliation of heaven and earth.

What I am calling for is the rescue of the passage mounds from the archaeologists' operating table, and their restoration as sites of spiritual significance. Here in Tipperary, the Rock of Cashel is abandoned to tourism, and it is part of the OPW lease that it is not to be used for religious purposes. The Derrynaflan chalice is locked in a glass case in the museum. For a thousand years it lay hidden for fear of the Vikings. Now the Viking city of Dublin holds it and no one asks for it back. The only grail chalice that we care about is the Sam Maguire football trophy.

I humbly suggest that the time has come to reclaim the roots of our religion – and reclaim for the pilgrim the sacred and ancient landscape that is being lost to the mere tourist.

Gillies Macbain is an organic farmer.