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HORUS VOL I. Issue 2
Stonehenge: What Was It?
by Alban Wall
There is a celestial phenomenon that numerous ancient civilizations, in their early study of the heavens, soon discovered and put to use in helping to regulate their civil and religious affairs. Simply stated it is
"The phases of the Moon exactly repeat themselves on the same days of the year every nineteen years, but not in any year in between."
Since early times, and even in some cultures today, the waxing and waning of the Moon has been the astronomical basis of the month. The Moon circles the Earth once in a fraction over 29.5 days. During that
time it completes one set of phases. It was quite obvious to ancient observers that coordination of lunar months with solar years could provide a natural, ready-made calendar cycle. There are many examples in
ancient history of luni-solar calendar systems based on the fact that there are 235 lunar months in 19 solar years. I will state at the outset that this was the purpose, or at least the end result, of the mysterious
megalithic structure called Stonehenge.
Since the solar year contains 365¼ days, the lunar month 29½ days, and the Sun-Moon cycle 19 years, we should expect these numbers to be prominently reflected in the design of the site. This is indeed the
Over the period of its development, Stonehenge was, in turn: an observatory, a calendar, and finally, a temple. In its last stage it was probably all three combined. I will examine separately those components
which are basic to the theme of this paper, presenting my reasons and arguments as to the purpose and operations of each. I will then integrate the elements to show how they functioned perfectly together as a
truly remarkable astronomical clock.
[*!* Image: Figure 1 -- The Stonehenge 19-year Lunar-Solar Calendar
The Sun Circle is used to count the days in a year by advancing a marker stone two holes each day, except on the summer solstice. Thirteen times around the circle gives 13 x 28 = 364. The lunar circles are
used to count the days of a lunar month by advancing the marker one hole each day, first around the Y-Circle, then around the Z-Circle. The Sarsen Circle symbolizes the 29.5 days of the month, one megalith
being half size. The trilithon horseshoe represents the phases of the moon. The Year Dial is used to count the 19-year cycle of 235 months. LABELS: SUNRISE. SUNSET. SPRING. SUMMER. WINTER.
AUTUMN. SUMMER SOLSTICE. WINTER SOLSTICE. SUN CIRCLE. LUNAR CIRCLE. SARSEN CIRCLE. Y HOLES. Z HOLES. DARK HALF. LIGHT HALF. YEAR DIAL]
The Sunrise and Sunset Zones
In the drawing [see Figure 11 these are labeled Sunrise Horizon and Sunset Horizon. On the first day of summer, sunrise occurs at a point on the horizon very near the Heelstone when viewed from the center of
the monument. This is the time of the summer solstice, the longest day of the year. Each day thereafter the Sun rises a little further to the South. In three months it will rise due East at a point indicated in the
drawing as the Equinox, when day and night are equal. In another three months it will rise at the point marked Winter Solstice. Here it reverses direction and sunrises now begin to occur a little to the North
each day. After three more months, sunrise will take place due East at the point marked as the Equinox, and in another three months it will occur once again at its original starting point near the Heelstone.
Yearly sunsets occur in a similar manner within the area marked Sunset Horizon. The arrows in these zones indicate both the range and direction of sunrises and sunsets during the four seasons.
The Sun Circle
(The Aubrey Circle)
At some point in time the designers of Stonehenge had already determined, most likely by carefully noting the annual shift of sunrises along the horizon, that the solar year consisted of close to 365 days. The
first of their observations at the site was for the purpose of more accurately refining this value. They accomplished this with a ring-counter, labeled Sun Circle in the drawing. Approximately 285 feet in
diameter, this component consisted of 56 evenly spaced holes which were filled with chalk for easy visibility. In the counting procedure each hole represented a half-day, two holes a full day. The complete
circle thus contained, or represented, 28 days. Thirteen turns around the circle equaled 364 days, which they assumed as the value of the base year for computational convenience. The objective was to
determine by how much the true length of the solar year exceeded the base year of 364 days and from this the accurate value of the solar year itself.
The ring counter would be used to determine the length of the year as follows:
At the end of, say, a 33-year span of observations, the marker stone would be found to be 82 holes (41 days) beyond where it would be if the year were only 364 days long. To calculate how much greater than
364 days the year is, 33 years is divided into 41 days, which comes out to be slightly less than 1¼ days (1. 24). This added to 364 gives 365.24 days, which is very close to the true length of the solar year.
Many investigators of Stonehenge have pondered over why the number 56 was chosen in constructing the Sun [Aubrey] Circle. The preceding provides the answer; 28 days and 13 cycles are whole number
factors of 364 days. The 56 evenly spaced holes are twice 28 and simply subdivided the base cycle of 28 days in two. To count days around the circle, the marker was moved twice a day, probably one hole at
sunrise and another at sunset.
It will be noted in the drawing that one hole of the circle, number 22 was set in line with the point of the horizon where it had already been determined that the Sun rose furthest North. This orientation of the
circle toward the summer solstice was not a result of coincidence, but of purposeful design, as will become evident. I suggest that the Sun Circle was used to measure the length of the year as follows:
A marker stone was set at hole 22. On the morning of the summer solstice, identified by precise observation of the Sun's position at sunrise, the marker was moved one hole clockwise and an additional hole
clockwise at sunset; two holes per day. At this rate the marker completed one turn of the circle and was back at hole 22 in 28 days. In 364 days it made 13 turns of the circle at which time it was again at hole
22. Of course, it was also at hole 22 every 364 days thereafter.
In the meantime, sunrises visibly shifted southward along the horizon from the beginning alignment with hole 22 to an alignment with hole 28 on the winter solstice. Here, the southward shift reversed direction
and arrived back in alignment with hole 22 after the passage of one full year. This "pendulum" movement of sunrises (and sunsets) along the horizon repeats itself each year. If the true length of the solar year
were exactly 364 days, both the Sun and the marker would have returned to exact alignment with each other, at hole 22, every 364 days. However, the marker stone, at each successive summer solstice sunrise,
advanced further and further beyond hole 22, indicating thereby that the true solar year was slightly longer than the assumed 364-day base year. When it became evident that the year was consistently at least
365 days, this was taken into account by not advancing the marker on the day of the solstice. The magnitude of the remaining error was readily determined by maintaining the 365-day count over a period of
many years to determine the average number of years for an error of one day.
The Two Lunar Circles
(The Y and Z hole Circles)
The next phase of the overall project was to determine the average length of the lunar month the time required for the Moon to go through one complete set of phases. This was accomplished by the same
method employed in calculating the solar year.
They had already determined through years of observation, that the lunar month was somewhere between 29 and 30 days in length. A ring counter of 60 holes would have been ideal for accomplishing their
purpose. The remains of such a 60 element circle have been found near the central area of the monument and this very well may have been originally used.
However, I call the reader's attention to the 2 Lunar Circles in the drawing, also labeled as the Yand Zholes, respectively. The Y-hole circle contains 30 holes and in the original scheme represented a lunar
month of 30 days. The Z-hole circle contains only 29 holes and represented a lunar month of 29 days, the average of both circles being 29. 5. By moving a marker around each of these circles alternately at the
rate of one hole space per day, the marker made two complete revolutions in 59 days, averaging one revolution in 29.5 days. This was the assumed value of the lunar month against which actual observations
were measured and compared over a long period of time.
By starting the marker in motion at a specific phase of the Moon, it would return to the starting point at the same phase each time if the true length of the month were the assumed value of 29.5 days. However,
after each cycle the marker was found to advance further and further beyond the starting point, indicating thereby that the month was actually longer than 29.5 days.
Here, too, they were able to determine the average monthly overrun by dividing the total number of months of observation into the total overrun, and from this, the true length of the month itself. Of course, the
longer the period over which observations were made, the greater the expected degree of accuracy. Using this procedure, they would have found that, in the long run, an error of one day accumulated in 33
The Sarsen Circle
Consisting of 30 upright megaliths with connecting lintels, one being half as large as the others, this component was part of the temple design of Stonehenge and was not used in the actual measurement of the
calendar month. Here, the 29112 megaliths symbolize the 291/2 days of the lunar month. Each megalith is aligned with a hole of both the Y-and Z-circles, and the complete circle, just as are the others, is
oriented around the common central axis (labeled Vertical Axis in the diagram).
This upright megalith was used in conjunction with other now missing megaliths to form a sighting avenue down which an observer at the center of the monument could observe, with great accuracy, the
azimuth of the summer solstice Sun as it rose above the horizon.
The Trilithon Horseshoe
The elements of this component of Stonehenge are labeled Tri. 1 through Tri. 5 in the drawing. The Trilithon Horseshoe shares the same orientation toward the horizon as the previously described components.
It was a part of the temple aspect of the monument like the Sarsen Circle. Each trilithon consisted of 2 upright megaliths with a connecting lintel. Spaced 60 degrees apart, the trilithons graduate in height with
Tri. 1 and Tri. 5 being the shortest, Tri. 2 and Tri. 4 of middle height and Tri. 3, commonly called the "Great Trilithon", the tallest of all. I have symbolized their height differences by exaggerating their widths
in the diagram. The Trilithons themselves, by their increasing and decreasing heights, symbolized the waxing and waning of the Moon over the full span of the lunar month.
The five Trilithons relate to the Sarsen Circle, and thus also to the Y- and Z-hole Circles, in the following manner: recalling that the Sarsen Circle symbolized the lunar month, note also that the Trilithons are
individually aligned both with the centre of the Monument and with specific arches on the Sarsen Circle. Since each of these is 5 arches, or days, apart, it seems obvious that the Trilithons symbolized specific
phases of the moon in 5-day units. (This is similar to the modern practice of indicating the Moon's phases -- crescent, half, full, etc. -- within specific date blocks on wall or desk calendars.)
Since the Trilithons are graduated in height, Tri. 3, the "Great Trilithon", symbolized Full Moon, as it is the tallest of the five. I have numbered the Sarsen arch at this point as "day 15", halfway through the
cycle toward the next New Moon. The point on the Sarsen Circle directly opposite Full Moon would be New Moon, and this arch is numbered "day 30", (which would in reality be day 29112). Since the sizes
of the Trilithons have given us the clue to the proper orientation and numbering of the lunar day-counting device, we can now follow the marker stone in its monthly journey.
To begin, we place the marker at arch 30, day 30, at the time of New Moon. Note that there is no Trilithon at all at this point of the Horseshoe. Since the Horseshoe symbolizes the waxing and waning of the
Moon throughout the lunar month, though the space for it is there, absence of a Trilithon at this particular point is understandable; when the marker is here the Moon is new and therefore, invisible; no Moon, no
Each day the marker was moved one space clockwise on the Sarsen Circle. After 5 days the marker was aligned with a small Trilithon and at this time the Moon itself would have been a waxing crescent. At
day 10 the marker was in line with a larger Trilithon and the Moon was now gibbous (more than half illuminated) and still waxing. At day 15, the marker was at the Great Trilithon with the Full Moon shining
forth in maximum brilliance. At day 20 the marker was again at a medium-sized trilithon, the Moon gibbous once more, but now waning. At day 25 the marker reached the second of the smaller Trilithons
while, in the sky, the Moon had waned again to crescent. The marker completed its monthly journey at day 30 (arch 30), and the Moon was invisible once more.
To recapitulate, as the marker moves around the Sarsen Circle it accurately reflects the correct phase of the Moon by the size of the Trilithon with which it is aligned. As the Moon successively waxes and
wanes, so too the Trilithons become larger and then smaller. just as we are able to tell the position of the Sun in the heavens by observing the hour hand of a clock, the location of the marker stone on the lunar
circle accurately indicates the Moon's phase at all times, no matter for how many consecutive days and nights the Moon itself may have been totally hidden by clouds.
The Year Dial
This horseshoe of upright stones, as can be seen in Figure 1, is situated just inside the Trilithon formation. It is composed of 19 elements and was the component used to keep track of the 19 years of the Sun-Moon calendar cycle. A marker was moved around it at the rate of one stone per year.
The Operational Mode of the Calendar
Earlier I stated that the 3 numbers which are fundamental to a 19-year Sun-Moon calendar, 365¼, 29½ , and 19 - the lengths of the solar year, the lunar month, and the Sun-Moon cycle, respectively ought to be
prominently reflected in the design of Stonehenge. In my explanation of the separate operation of each component, I have shown that these numbers are clearly evident. The number of days of the solar year
were expressed in the Sun Circle where 13 revolutions of a marker around that circle were accomplished in 364 days. By not advancing the marker on the day of the solstice, and skipping an additional day
every four years, the movement of the marker around the circle could be kept in synchronization with the annual shift of sunrises along the horizon. Long term divergence was corrected by an additional
intercalation whenever such divergence reached one full day.
The 29½ days of the lunar month were reflected in the average of the 30 Y- and 29 Z-holes. Here, too, long term divergences between the movement of the marker around those circles and actual phases of the
Moon were corrected whenever the difference reached a full day. This could be done by moving the marker twice in succession around the 30-hole circle.
The number of years of the Sun-Moon cycle is self evident in the 19-element Bluestone Horseshoe.
I have shown how each of the calendar's components operated separately to perform their individual functions. In what follows, I will "engage the gears" of the calendar device so that the reader may see how
perfectly they mesh.
Note that a line drawn from hole eight of the Sun Circle through hole 22 and out past the Heelstone divides the monument into symmetrical right and left halves. I have referred to this as the Vertical Axis. To
start the calendar in motion, all three markers ("clock hands") are set in alignment with each other along the Vertical Axis at the following points of their respective dials:
- Sun marker - at hole 22 of the Sun Circle
- Moon marker - at day 23 of the Y-hole circle
- Year marker - at year 19 of the Year Dial (which is the end-point of the preceding cycle).
This is an arrangement similar to the alignment of the second, minute, and hour hands of a clock.
At a specific concurrence of two celestial events, New Moon and summer-solstice sunrise (which occurs once every 19 years), the markers are set in motion at the same rate as previously described for each
component separately, the Sun marker two holes clockwise per day, the Moon marker one hole space per day, and the Year marker one stone per year. (At the end of the first year, the latter would be moved to
stone number one.)
At the start of the cycle, not only are the 3 hands of the calendar in alignment along the Vertical Axis, but the Sun and the New Moon will also rise together along that same alignment, though the Moon itself
will not be visible.
From that time onward, because of their different rates of motion, the 3 markers will present a scattered appearance and will not again come into alignment with each other along the Vertical Axis until 9½ years
have passed, which marks the midpoint of the 19-year cycle, when the Sun marker will be at hole 8 of the Sun Circle, the Moon marker at day 8 of the Z-hole Circle, and the year marker at year 9½ of the Year
Dial. Whereas the start of the cycle occurred at sunrise of summer solstice with the Moon at new phase, the midpoint will occur at sunset of winter solstice with the Moon at full phase. In fact, on that very day
the Sun will actually set along the Vertical Axis in line with hole eight of the Sun Circle while, at the same time, a Full Moon will be rising in the vicinity of the Heelstone, a striking visual confirmation of the
remarkable accuracy of the Stonehenge ring-counter calendar.
From here on the markers will again become scattered, but, on the 1st day of the 19-year cycle, all three will once more return to their original alignment along the Vertical Axis, while the summer solstice Sun
and a New Moon are set to rise together again near the Heelstone.
One 19-year cycle has ended and another is about to begin. By use of their calendar device, they were able to keep continuous track of the following chronometric units:
Days, weeks, months, seasons, years, Moon phases, and 19-year Sun-Moon cycles.
With all its components put back into place, the calendar would function as efficiently today as it did then simply by operating it in the manner I have described. Though this is extremely compelling internal
evidence that the monument was in fact a 19-year Sun-Moon calendar, there is also indirect historical testimony to the fact. Diodorus Siculus, a Roman writer of the Ist century B. G, referring to "an Island in
the ocean beyond the land of the Celts [Gaull" declared that its inhabitants were familiar with, and used, the 19-year calendar cycle. But there is even more direct evidence bearing on the matter. A bronze Celtic
calendar plate, now known as the Coligny Calendar, dating to about the first century B. G, was discovered in a vineyard in France. I have made an extensive study of the plate's contents and have been able to
determine that the format of the calendar, including several features that hitherto have been considered unique to it, are actually duplicated in the Stonehenge scheme. There is a strong possibility that the
Coligny plate is the document form of the 19-year calendar that had been discovered and perfected at Stonehenge over many years of actual celestial observation. This is especially so in view of a cryptic
statement of Julius Ceasar, in his "Commentaries", that "knowledge of this is thought to have been discovered in Britain and from thence to have been carried across the sea to Gaul."
Discoveries of ancient calendars in widely scattered sections of the globe- the European continent, Japan, the Rocky Mountains, and, most recently, Mexico city - which contain numerous calendric features
strikingly similar to those contained in the Stonehenge format, provide exciting evidence of a possible common calendar system as early as 500 B. C. These, and other matters touching on the same general
subject, will be presented in future issues of HORUS.