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Alignment of chamber top hole at Newgrange
Like the roof box at Newgrange, the top hole of the chamber (normally covered
by the capstone) could also have an archaeoastronomical meaning. Look at
the following figure:
The red color depicts the measurements (the red rectangular ACDE
is the projection of the top hole under the capstone on the ground plan)
made during my visit at Newgrange on Dec. 20, 1996:
All the (red) dimensions have been measured by using a 2D
water leveled laser pointer and detailed maps of O'Kelly.
height (h) difference between the underside of the cap stone and top plane
of the basin in the central recess (B) is around 6150 +/- 100 [mm] (including
an approximated lowering of the roof in time by 500 [mm] [O'Kelly (1982),
distance between the most southern corner of the top hole (A) and the stone
C8 (B) is 4610 +/- 100 [mm].
the top hole has a dimension of 915 x 750 x 1000 x 1000 +/- 40 [mm] (AC
x AD x CE x DE). Point E has not been determined directly, but by using
Look how close point A is to the main path of the winter solstice sun!
AC is turned some -30o +/- 1o from the main passage
azimuth and AD is some 65o +/- 1o turned from the
main passage azimuth.
there is no blockage of the light going from the top hole under the capstone
(A) towards C8 (B).
the passage azimuth (azipas) is around 135o +/- 1o
(Tim O'Brien, 1996, pers. comm)
O'Kelly (1982) is showing in his pictures something about 148o
- 150o. This is not correct. According to Tim O'Brien, O'Kelly
has acknowledged this error.
Taking this into account, we get the following information with
regard to the light patches in the central recess at the level of the top
of the basin during summer solstice day on 3050 BC:
The size of the picture is: 2080 x 1400 [mm]
The error in the colored pixels
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 been
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 capstone
Light patch around 10:10 GMT
Light patch around 10:30 GMT
Light patch around 11:00 GMT
Everything that will be covered with light during the above time period
(including the inaccuracy of +/ 150 [mm]).
The contours of the broken basin in the central recess.
So to summarize: The sun shines through this top hole under the capstone
some 30 days before and after the longest day on the plane of the basin.
During the longest day it will shine some 50 minutes on this plane, if
there was only a small aperture through the top hole.
Just for comparison, the sun shines through the roof box (at winter
solstice) some 5 days before and after the shortest day in the chamber
and during the shortest day it will shine some 15 minutes in the chamber.
Another remarkable thing is; the altitude of A with regard to
B is 53o 9' has almost the same value as the latitude of Newgrange
(53o 42'), so (is there logic behind this so?) every
day one can see at a certain moment, through the top hole, the ecliptic.
It looks like that there could be an alignment between the top hole and
the basin in the central recess of Newgrange. The above information was
not determined with very small inaccuracies, but even the present inaccuracies
provide a good general idea.
A circular cone of stones over the chamber
can be seen up to the level of the capstone. This could indicate that some
time the chamber was covered with a nice circular cone of stones which
let the capstone almost free.
Remember that, as somebody said, every roof is pointed towards the heaven
and thus would possibly allow the high/midday summer solstice sun inside.
This is true of course (you can also see this, due to the small influence
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 buildings
in the neighborhood.
Another increase of likelihood is if the same phenomena is seen in
other corbelled roof. It is a pity that not many corbelled roofs survived
the years. Looking at data on Knowth, the top
hole of Knowth also seems to act in the same way. If there exist more original
corbelled roofs, please let me
I thank Clare Tuffy, custodian of Newgrange, for allowing me to do the
Through the custodian of Newgrange, I got into contact with Gerry Bracken,
Ireland. He had done, between 1991 and 1993, comparable measurements with
regard to the top hole under the capstone. The difference between his work
and mine is that he thought that the light would shine in the right recess
chamber (which will not happen, in my opinion).
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Major content related changes: August 22, 1997