Now we can examine the 2 passageways that cut through
the heart of Knowth monument. The Western passage measures 34m in length,
with a remainder of 80 orthostats out of a possible 94 that make up
the walls. The width averages 60cms and height approximately 1.1m.
3/4 of the distance into the passage it bends to the south before
opening up to the end chamber. This is a classic undifferentiated
style called 'Allee Coudee' after the French. (Note 5)Because its so long
only a narrow beam of light can extend all the way to Ortostats
33 & 34 on the left hand side as you face in.
The azimuth range
is restricted by a few leaning orthostats on the right side and
this curtails the azimuth to approx. 3°. i.e.
263° - 266° Outside the entrance lies a decorated
kerbstone (K74) and beyond that the yellow sandstone pillar
mentioned earlier.
This pillar is 2.56m high and 4.33m away from the K74 stone. K74 is approximately 96cms high, so therefore the pillar would cast a shadow over K74 when the Moon was between an altitude range of 20° - 30° above the horizon. This occurs 18 days before the Sun enters the passageway. In my proposed date of 5100BC that would have occurred around Apr 28 (their Vernal Equinox time Apr 30 - May 2).(see fig. below).
We can also clearly see(5100BC) that when the moon casts its shadow like this it marks a cyclical return measuring 19 tropical years(Metonic cycle,235 lunations). The moon only appears to work for the Vernal Equinox rather than the Autumnal at this side of the mound and was probably used to adjust for the gradual change in equinox days over a great range of decades,or centuries.
Now moving 19 years later (5081BC) we see the closest azimuths between the Sun and Moon falling on May 1st. with a 1.0° difference.
Again (5062bc, 0.1° difference) the Sun cannot be substituted for the Moon in this sky 'window' because then the sun sets further West after equinox time, only the Moon as the alternative luminary fits. The Sun's shadow however behaves differently and was used when the equinox times were much closer than days apart. Usually hours before the equinox times the Sun's shadow would form a column gradually moving across the face of K74 from the 273° azimuth towards 264° where there is a clearly demarcated vertical incised line running down the entrance stone dichotomising it in two. K11 on the eastern entrance exhibits some foreshortening on its longitudinal axis because its axis is not fully parallel with the N - S true cardinal axis. The Moon's shadow appears at the face of K74 within 1° of its vertical demarcation line and oscillates across it in a peak/trough fashion. Clearly the intersection of both Sun and Moon's shadows gave our monument builders the precise Equinox times, the Moon, of course ,casting a weaker shadow than the Sun, due to its first phase condition ,see drawing below.
