On March 17, 1980, Martin Brennan and Jack Roberts saw a beam
of light from the rising sun illuminate a carved stone at the back
end of the rock-lined passage in the great mound called Cairn T at
, County Meath. Two weeks later,
on the evening of the first of April, Brennan and his colleagues watched the rising moon
from the same spot. As the moon appeared over the horizon a shaft
of light was projected along the passage and onto the same carved stone.
The great passage mound of Knowth
, also in Meath, contains two
rock-lined passages, one facing east, the other west. Brennan
observed the setting sun shine into the western passage on
September 13, 1980. Attempting to observe sunrise on the following
day, he found that the view of the rising sun from the eastern
would be blocked by trees and the current level of the
ground. Nevertheless, it seems likely that the eastern passage was
also originally intended to be penetrated by light from the rising
sun and moon. Although solar alignments have been described at
many Neolithic sites in Western Europe, less attention has been
paid to lunar alignments, despite the fact that at certain times
the moon can rise or set at any location on the horizon which may be occupied by the sun.
Brennan's experience, described in his 1983 book The Stars and
suggested that these Irish Neolithic sites might have
had some connection with the moon as well as the sun. I have
identified another connection, previously overlooked by Brennan and
others working at Knowth. If moonlight were to shine on the back
stone of the eastern passage at Knowth, it would illuminate a map
of the moon itself, the world's oldest known depiction of the lunar maria.
The carved stone which forms the end wall of the eastern
was called Orthostat 47 by George Eogan
, who excavated
Knowth in the 1960s. The design has three sections,
superficially similar but oriented differently. The right-hand
section appears to be nothing less than a map of the lunar maria,
as becomes clear when it is compared with a naked-eye map of the
moon. At least a dozen points of correspondence are immediately obvious.
A naked eye map of the moon (left), a carving from Knowth Orthostat 47 (right)
and the two superimposed (centre) to illustrate their similarity.
The remaining two sections of the carving are simpler but
crudely similar to the first, sharing the overall arc shape of the
maria surrounding the lunar central highlands as well as an
isolated spot representing Mare Crisium. Why were they carved in
different orientations? I believe they depict the apparent
rotation of the maria on the disk of the full moon as it crosses
the sky in the course of a night. Watch the full moon one night.
The arc of maria opens to the right (like a letter C) as the moon
rises, opens downwards (to a northern hemisphere observer) as the
moon crosses the meridian, and opens to the left at moonset. The disk appears to rotate like a wheel, an illusion caused by
our motion on a rotating Earth. We compare the moon with our
apparently fixed horizon, but the plane of the horizon actually
rotates with the Earth to trace out a cone in space.
The right-hand carving on Orthostat 47 depicts the maria as
seen on a full moon a little after midnight. At upper left the
maria are shown soon after moonrise. It would be reasonable to
assume that the lunar disk continues to rotate beneath the horizon,
and the carving at lower left appears to show the maria 'upside
down' as if under the horizon. The only thing missing is a clear
outline of the circular limb of the lunar disk. Perhaps it was
originally chalked or painted on the rock.
Here on one stone are two important lunar observations,
representations of both the maria themselves and their apparent
rotation as the moon crosses the sky. Further examples of both are
found at Knowth. One of the most diagnostic is Kerbstone 52
designated by Eogan. Brennan called it SW22 or the 'calendar
stone'). On it a group of crescent shapes are arranged around the
Seven of the crescents at the top of the
stone are replaced by circles. Brennan interpreted the crescents
and circles as phases of the moon, though the characteristic first
and last quarters are not convincingly portrayed. However, the
crescents are not oriented as an actual lunar crescent would be in
any obvious sequence of observations. Rather, their positions
match the orientation of the maria as the full moon crosses the
sky. Why do they turn to circles at the top of the stone? I
attribute this to the excessive contrast between the brilliant full
moon and the black night sky, which renders the maria harder to see
than at dawn and dusk.
Near the base of Kerbstone 52 the crescents dip below a wavy
line (a schematic horizon of waves or hills?) and pass horizontally
back to the starting point to complete the cycle. Brennan
interpreted the cycle as a month, whereas I see it as the daily
motion of the moon. There are 29 symbols, the number of whole days
in a lunation, but that number, obviously associated with the moon,
does not by itself prove that the design is a depiction of a month.
The symbols cross a spiral which may represent the moon's path
through the heavens at a different elevation each month during the
year. Here again we see the maria represented by an arc, whose
changing orientation corresponds to the apparent rotation of the
lunar disk during a night. This general pattern, in various forms
and less fully developed, is repeated elsewhere at Knowth and at
Loughcrew, Newgrange, Dowth and perhaps at Gavrinis
The overall pattern of lunar maria from Humorum and Nubium
past Imbrium to Nectaris and Fecunditatis may be seen as one broad
arc. Alternatively, the eastern maria (Crisium, Nectaris and
Fecunditatis) suggest a three-fold subdivision of the arc. This is
extended westwards by Mare Frigoris, and the three-fold division is
again suggested (a little less obviously) by south-western Oceanus
Procellarum, Mare Humorum and Mare Nubium. Thus, various
combinations of arcs might be interpreted as lunar maps. Several
of the most complex examples are shown in the diagram to the right.
One of the most interesting of these additional maps is that
carved on a stone basin which Eogan discovered in the right-hand
recess of Knowth's eastern passage. This shows a set
of concentric circles (Mare Imbrium and its surrounding highlands),
multiple lobes to the left and right (Oceanus Procellarum and the
western maria respectively) and a small isolated circle near the
top (Mare Crisium or possibly the eastern end of Mare Frigoris).
All these carvings, but especially the map on the stone basin
and the carvings on Orthostat 47, which might have been illuminated
from time to time by the moon itself, suggest that the markings on
the moon - as well as the moon itself - were important to the
builders of Knowth. God, home of the gods or of departed spirits?
We will never know, but we can be certain that the builders of
Knowth were keen observers of the sky. Without using sophisticated
mathematics or fine angle measurements (as suggested by Alexander
Thom and others), these neolithic astronomers were able to observe,
depict and hypothesize about the moon and its motions. These are
the actions of scientists.
Possible lunar maps:
(a) Stone basin found in the eastern passage at Knowth.
(b) Knowth Kerbstone 97.
(c) Knowth Kerbstone 68.
(d) Stone G, Baltinglass, Co. Wicklow.
The carvings are about 4800 years old. The next oldest
depiction of the maria known to science is that by Leonardo da
Vinci in about 1505 AD. Other ancient lunar maps may lie
unrecognised among neolithic (and later) artifacts. For instance,
I note that the plan of Stonehenge is itself very like the shapes
I have described - a circle containing a horseshoe - and so might
be considered a very simple map of the moon. Its famous solar
alignment happens every year, but at certain times the full moon
would also rise over the Heel Stone, and would illuminate a map of
itself. This, of course, is even more speculative than the Knowth
alignment, and it is also somewhat more recent than Knowth.
For now the products of the artists - and scientists - of
Knowth are by far the oldest apparent representations of lunar
markings and motions known to us. Their significance to the
history of science is considerable. Knowth is one of the most
important ancient scientific sites in the world.
Lastly, I will raise a still more speculative matter. The
historian Diodorus Siculus (writing shortly before the time of
Christ but quoting Hecataeus, some five centuries earlier, 'and
certain others') wrote of the 'Island of the Hyperboreans':
... there is also on the island both a magnificent
sacred precinct of Apollo and a notable temple which is
adorned with many votive offerings and is spherical in
shape... They say also that the moon, as viewed from this
island, appears to be but a little distance from the
Earth and to have upon it prominences, like those of the
Earth, which are visible to the eye. The account is also
given that the god visits the island every nineteen
The nineteen year period is presumably that between almost
identical eclipses. The spherical temple has usually been assumed
to refer to the circular Stonehenge, but might equally well refer
to Knowth or Newgrange, which being prominent mounds at least
resemble hemispheres. Newgrange appears to have been partly
covered with white quartz fragments, giving the appearance of an
egg (according to Brennan) or of the shining moon itself. Quartz
is also found at Knowth and Dowth. Its original distribution at
each site is uncertain. Were the mounds themselves decorated to
look like the moon? This deserves further study. The
'prominences' referred to are presumably the lunar maria visible to
the eye, and the reference to them at least indicate a local
interest in those markings which is more in evidence at Knowth
than at Stonehenge
The text may even be a confused reference to the very carvings which are the subject of this article.
A more complete account of this research, but lacking the section on passage geometry, is to be found in:
Stooke, P.J. "Neolithic Lunar Maps at Knowth and Baltinglass, Ireland". Journal for the History of Astronomy, XXV: 39-55, 1994.
Dr. Philip Stooke 1994
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