it is possible that this kerbstone was used to calculate the exact
number of days in the tropical solar year. There are 29 moons
in total, 22 crescents and seven circular moons which are really
double circles, and potentially signifying an extra count. There
is a folk tale still in existence from Brittany to Scotland which
says that you should never count stones more than once because
you will never get the same number. The numbers and arrangements
at Stone Age sites were chosen so that there were several ways
of counting them.
we count the moons, to get 29, and add the second set of circular
moons, we get 36. If we double 36 (and the stone already suggests
doubling with the waved line - 2x31=62) we get 72, and add the
solar spiral, we get 73. 5 times 73 is equal to 365, the exact
number of days in the year. Every fourth year, add the solar spiral
to get 366. Another 'Lunar Stone'
at Knowth can also be used to calculate the exact length of the
year, as well as both the siderial and synodic lunar months.
"waved line" feature can also be seen to have supplemental
counts on the left side, continuing from 31 to 32, 33 and 34.
synodic months is also a significant subunit of the Metonic
Cycle, because when doubled it becomes 64 synodic periods
which ties in with five calendar synodic periods of Saturn. 33
synodic months is one-third of the very important metonic subunit:
99 synodic periods ends just two days after eight tropical years.
And 34 is one-quarter of another large Metonic subunit: 136 synodic
months ending about one day before 11 tropical years.
considering these engravings we must remember that the method
of observation does not require complex equipment or machinery,
and does not involve complicated mathematics. What it involves
is simple observation over long periods of time. These engravings
were obviously an attempt by the Neolithic astronomers to pass
on their knowledge to the next generation a quest in which
they succeeded. 5,000 years on we too can get an insight into
the astronomical observations of our "primitive" ancestors,
and we too can watch the heavens and observe the Metonic cycle
reading on the web:
cycles and time - a guide by Ivars Peterson.
and phases of the Moon - by Mike Wilson.
Church Lunar Calendar -based on the Metonic Cycle.
Kind thanks to Professor George Eogan, director
of excavations at Knowth, for his kind permission to access the
site and take photographs.
I am also greatly indebted to Charlie Scribner, who has opened
my mind to the lunar cycles with his authoritative writings and
pages of interest:
Metonic Cycle - an illustrated lesson on how it works.
Another lunar stone - calculating
the siderial and synodic months, and the length of the year at
sunlight at Knowth - Sunlight in the western passage.
Knowth west - 5,000-year-old megalithic engravings.