Alignment of eastern chamber top hole at Knowth
Like the top hole at Newgrange, the top hole of
eastern chamber at Knowth (normally covered by the cap stone) could
also have an
The projection of the top hole on the ground plain and the
in the right recess can be seen in the following picture:
The red color depicts the measurements (the polygonal ABCDE is
the projection of the top hole under the capstone on the ground plan)
during my visit at Knowth on August 18, 1997:
All the (red) dimensions have been measured by using a 2D
water leveled laser pointer and detailed maps of Eogan.
height (h) difference between the underside of the cap stone and top
of the basin in the right recess (F) is around 5980 +/- 100 [mm]
an approximated lowering of the roof in time by 500 [mm] [O'Kelly
distance between the most southern corner of the top hole (B) and the
54 (F) is 4670 +/- 100 [mm].
the top hole has a dimension of 1120 x 330 x 700 x 550 x 800 +/- 40
(AB x BC x CD x DE x EA). Points D and E have not been determined
but by using a photograph.
AB is turned some -45o +/- 1o from the main
azimuth and BC is some 48o +/- 1o turned from the
main passage azimuth.
there is no blockage of the light going from the top hole under the
(B) towards orthostat 54 (F). Also the jamb stones don't stand in this
path. Points A, D and E are blocked due to roofstone of right recess.
the passage azimuth (azipas) is around 85°.
Taking this into account, we get the following information with
to the light patches in the right recess at the level of the top of the
basin during summer solstice day on 3100 BCE (18/7/3100 BCE):
The size of the picture is: 2800 x 2950 [mm]
The error in the colored
in x and y direction are: +/- 150 [mm]
Description of the colors:
To get this effect the capstone should have been removed or just have
moved to allow for a small light patch, which could have been possible
during the time the cairn material was not yet fully covering the
Light patch around 12.42 GMT
Light patch around 13.02 GMT
Light patch around 13.32 GMT
Everything that will be covered with light during the above time period
(including the inaccuracy of +/ 150 [mm]).
The contours of the basin in the right recess.
So to summarize: The sun shines through this top hole under the
some 47 days before and after the longest day on the top plane of the
During the longest day it will shine some 50 minutes on this plane, if
there was only a small aperture through the top hole.
It looks like that there could be an alignment between the top hole and
the basin in the right recess of Knowth. The above information was not
determined with very small inaccuracies, but even the present
provide a good general idea.
According to G. Eogan (pers. comm., 1997), no evidence is available
that the space above the capstone was held open for a long time. It
that it will have been blocked at the same moment the whole cairn was
Remember that, as somebody said, every roof is pointed towards the
and thus would possibly allow the high/midday summer solstice sun
This is true of course (you can also see this, due to the small
in the direction of the passage and the height of the chamber), so this
top hole-basin alignment is of course no proof. The likelihood of an on
purpose alignment is higher, because there are more alignments in this
monument and other monuments and there are alignments towards other
in the neighborhood.
Another increase of likelihood is if the same phenomena is seen in
corbelled roof. It is a pity that not many corbelled roofs survived the
years. Looking at data on Newgrange, the top
of Newgrange also seems to act in the same way. If there exist more
corbelled roofs, please let me know.
I thank Grainne Kelly and professor George Eogan for allowing me to do
the measurements. Furthermore I would like to thank Michael Walsh for
me to George Eogan.
Disclaimer and Copyright
Major content related changes: August 25, 1997