Computer animation shows how 5,300-year-old carvings at Knowth megalithic tomb depict 19-year moon cycle
The apparently complex nature of the moon’s movements sometimes leaves even astronomers struggling to understand and explain them. I’ve found over the years that trying to explain the Metonic Cycle – a 19-year cycle of the moon which brings its movements back into harmony with the solar year – difficult to say the least, especially to non-astronomers.
In 2009, I invited author and artist Martin Brennan to Ireland to speak at a conference in his honour. In the 1980s, Brennan made many fascinating discoveries and put forward interesting theories about the complexity of ancient astronomical study among the people who built the Boyne Valley megalithic monuments along with those of Loughcrew, Sligo and other parts of Ireland. He was the one who gave Kerb 52 at Knowth its new name – the ‘Calendar Stone’. This was based on his hypothesis that carvings on the stone could represent an attempt to enumerate and symbolise the 19-year cycle (which was known in Irish as Naoidheachta, meaning ‘The Nineteenth’, and also Baisc-Bhuidhin (the golden number).(1)
It is Brennan’s contention that Kerb 52 at Knowth can be used to track not only the phases of the moon, and its monthly synodic period, but also the much longer cycle which has become known as the Metonic Cycle because it was supposedly discovered by a 5th Century BC Greek astronomer called Meton. There are 22 crescent shapes on the stone, and seven circles, with a waved line in the centre, and some other features.
Chris Bruno, a long-time friend of Brennan’s, who met Martin in the United States shortly after he left Ireland in the mid 1980s, was a key contact in making the 2009 Boyne Valley Revision conference happen. If it hadn’t been for Chris, I’d never have been able to bring Martin back to Ireland. And so when Chris showed me the research he had done in trying to better understand Martin’s work, it was agreed that he would also speak at the conference.
In the above video from the conference, Chris shows a computer animation that he had specially made for the event by a computer programmer. This animation shows in a simple-to-understand way how the stone can be used to count the 235 synodic lunations of the 19-year Metonic Cycle. It’s a very clever piece of work and has to be seen to be enjoyed.
(1) Murphy, Anthony, Newgrange Monument to Immortality (Liffey Press, 2012)
For the purpose of explanation, the term ‘synodic month’ relates to the time it takes the moon to go from a particular phase, eg full moon, back to that phase. This is approximately 29.5 days.