© Copyright 2015 Rick Doble
Measure what is measurable, and make measurable what is not so.
The purpose of this article is to compare the scientific accuracy and precision of two methods of determining the day of the winter solstice: that of the Neolithic builders of the Newgrange passage tomb in Ireland around 3000 BCE and that of the Roman Empire 3000 years later around 0 CE. It is my contention that the Neolithic method of capturing light in a massive 'spot dial' was equal to or superior to the Roman method of sighting the sun at noon over a period of days and then interpolating the time of the solstice. I believe I can support this argument with available research.
But before I make my argument, I would like to give my readers a bit of
background and a personal story. Once
when I was teaching an advanced photography workshop, my class went
on a field trip to the Duke University greenhouse in Durham, NC in the winter.
As we walked in, a student saw a flower in perfect light, lit by a
shaft of sunlight coming down through the leaves of vegetation above
it. He reached for his camera but then realized he was at the end of
a roll of film, so he quickly rewound the exposed roll and put in a
new one. But when he turned around about a minute later the flower
was in shadow and the shaft of light had moved onto a leaf next to
it. It was then that I realized how quickly the sun moves and how
precisely moving light from the sun could be marked.
As a professional photographer for 40 years and the author of 3 books
about the craft and art of photography along with a MA in Media, I
understand how light works. Photography (literally meaning 'light
drawing' from the Greek) is the medium of light. Photographers are
craftsmen and artists who work with light and because of this, I
believe photographers are more sensitive to light and its effects
than non-photographers. So it is with this background I approach the
subject of the remarkable 'light instrument' at the Newgrange
See my resume.
The Duration Of The Winter Solstice
...the sun appears to halt in its incremental journey across the sky and change little in position during this time.
It is important to note that at the winter solstice the sun barely moves (i.e., the sun's declination). In fact the word solstice means just that. It comes from the Latin 'solstitium' meaning "point at which the sun seems to stand still" (dictionary.com). While modern scientific explanations assert this happens only on one particular day and after that the days get longer -- this is not quite true. The length of the shortest day and longest night can remain almost the same (within a few seconds) for about week. Because the sun 'stands still' for a number of days with very little movement, it is hard to determine the precise day that the solstice occurs.
The changes in Solar declination become smaller as the sun gets closer to its maximum/minimum declination. The days before and after the solstice, the declination speed is less than 30 arc seconds per day which is less than 1/60 of the angular size of the sun...This difference is ... impossible [ED: to detect] with more traditional tools like a gnomon or an astrolabe [ED: ancient tools the Romans and Greeks would have used]. It is also hard to detect the changes on sunrise/sunset azimuth due to the atmospheric refraction changes. Those accuracy issues render it impossible to determine the solstice day based on observations made within the 3 (or even 5) days surrounding the solstice...
Measuring the difference in the sun's movement at the time of the solstice was impossible with Greek and Roman tools and is barely "detectable with indirect viewing based devices like a sextant equipped with a vernier" which were not available until the 18th century. (http://en.wikipedia.org/wiki/Solstice)
The following was the method almost certainly used by the ancient Romans & Greeks:
It is most likely, then, that equinoxes and solstices were determined by observing noon solar altitudes for a series of days before and after the events. [ED: My emphasis] When the Sun is crossing the meridian at noon, it is relatively easy to measure its altitude, and then knowing the geographical latitude, to compute the declination. From the declination, it is easy to compute the Sun’s position on the ecliptic (the longitude), and we know that Hipparchus knew how to do it. But it is only at noon that such an easy determination is possible. It is then fairly straightforward to estimate the time that the Sun’s declination reaches some specific targeted value: 0° for an equinox, and maximum or minimum for a solstice. That series of daily altitude measurements were used to determine the time of cardinal events can hardly be doubted, even though no surviving ancient source has documented such an episode. Especially for the solstices, it is essentially the only viable option... [ED: My emphasis]
Dr. Dennis Duke, Four Lost Episodes in Ancient Solar Theory, Journal for the History of Astronomy (2008) http://people.sc.fsu.edu/~dduke/episodes3.pdf
The Newgrange winter solstice alignment was first observed by renowned archaeologist, Professor Michael O'Kelly about 50 years ago:
Over the course of the early excavation, some of the many local visitors would often tell the O'Kelly's of a tradition, that the rising sun, at some unspecified time, would light up the triple spiral stone in the end recess of the chamber at Newgrange. Some minutes before sunrise on the 21st of December 1967, Professor O'Kelly stood alone in the darkness of the chamber at Newgrange, wondering what, if anything, would happen. To his amazement, minute by minute, the chamber grew steadily lighter and a beam of sunlight began to enter the passage and to travel inwards, "lighting up everything as it came until the whole chamber – side recesses, floor and roof six metres above the floor – were all clearly illuminated". http://www.newgrange.com/michael-j-okelly.htm
After about 50 years since it was first discovered, there is now general agreement that the passage and chamber at the Newgrange passage tomb in Ireland is aligned with the winter solstice and that around the time of the solstice and only then, light falls down the long passageway to the farthest part of the chamber.
Once a year, at the winter solstice [the sun] shines directly along the long passage into the chamber for about 17 minutes and illuminates the chamber floor. This alignment is too precise to be widely considered to be formed by chance...Today the first light enters about four minutes after sunrise, but calculations based on the precession of the Earth show that 5,000 years ago, first light would have entered exactly at sunrise.
Document of the US space agency NASA. http://spacemath.gsfc.nasa.gov/SED11/P8Newgrange.pdf
The key piece of the Newgrange design was a 'roof-box' or 'light-box' which controlled the way light came into the passage. It was built with carefully crafted baffles that restricted the entry of light to the time of the winter solstice and also so that the light only came in at sunrise.
For 17 minutes, therefore, at sunrise on the shortest day of the year, direct sunlight can enter Newgrange, not through the doorway, but through the specially contrived slit that lies under the roof-box at the outer end of the passage roof.
O'Kelly, Michael J., and Claire O'Kelly. Newgrange: Archaeology, Art, and Legend.
As a photographer it struck me, that the setup at Newgrange is very much like a camera: there is an opening with a lens or aperture, there is a dark chamber (the word camera is derived from the Latin, camera obscura, meaning ‘dark chamber’), there is an exposure (a period of time that light is allowed into the camera and then shut off), i.e., the 17 minutes that the light shines down the hallway each morning and only during the time of the winter solstice. Plus, like a camera there is a point of focus, i.e., the day of the solstice when legend has it that the light shines down to the furthest chamber and illuminates the stone with triple spirals. In fact, the Newgrange instrument has many similarities to a pinhole camera whose origins go back into prehistory. For example, it was already a well known phenomena when it was examined by Aristotle in the fourth century BC. The discovery of the pinhole effect is based on a common occurrence:
The camera obscura [ED: pinhole camera] works on a naturally occurring phenomenon...and can, for example, often be observed when sunlight filters through dense leaves.
Because of Newgrange's striking similarity to a camera, I dug a bit deeper on the Internet and found the following by Martin Brennan, a respected researcher, who discovered the following about a Neolithic structure related to and not far from Newgrange:
In 1980 Irish-American researcher Martin Brennan discovered that Cairn T in Carnbane East is directed to receive the beams of the rising sun on the spring and autumnal equinox - the light shining down the passage and illuminating the art on the backstone. The Cairn T alignment is similar to the well-known illumination at the passage tomb at Brú na Bóinne (Newgrange), which is aligned to catch the rays of the winter solstice sunrise.
Here is what Martin Brennan said about his discovery:
Suddenly, I stared in amazement as this beam of light began to register against a stone bearing measured inscriptions. As the day progressed, the beam of light slowly moved from west to east across the stone, the sequence being measured by the inscriptions. This observation provoked a chain reaction of intriguing thoughts. First of all, if there was any sundialling, it was advanced sundialling. They were using a ray of light. This is called a "spot" dial and it is a considerable advance over using a shadow. Secondly, a gnomon, which is simply a stick used to cast a shadow, is thought to be the first scientific instrument and its earliest uses can be placed over twenty thousand years ago, back in the Ice Age. A progressive development of this leading to the use of a spot dial could exploit the full potential of the instrument and its astronomical implications.
spot dial is, in a sense, the opposite or negative of a traditional
sundial, i.e., it is the reverse of a sundial that casts a shadow.
Instead of capturing a shadow that is cast by the sun, a thin beam
of light from the sun is captured in a dark chamber where it can be
The spot dial at Newgrange magnified the movement of the sun at the winter solstice when the sun's movement was particularly hard to detect. With the right construction the movement of the sun can be magnified significantly. Here is O'Kelly's description of the movement.
...minute by minute, the chamber grew steadily lighter and a beam of sunlight began to enter the passage and to travel inwards, "lighting up everything as it came until the whole chamber – side recesses, floor and roof six metres above the floor – were all clearly illuminated" http://www.newgrange.com/michael-j-okelly.htm
In addition O'Kelly also stated that in 17 minutes the 'first pencil' of direct sunlight widened to a 17cm band and then narrowed before disappearing entirely. (O'Kelly, Michael J., and Claire O'Kelly, Newgrange: Archaeology, Art, and Legend)
J. Partrick, who investigated the alignment, at the request of
Professor O'Kelly, found that originally the maximum width of the
light would have been 40cm. The beam of light is now only 17cm
because "...some of the stones are now leaning inwards, thus
trimming down the width of the beam of light." (J.
sunrise at Newgrange, Nature,
At exactly 8.54 hours GMT the top edge of the ball of the sun appeared above the local horizon and at 8.58 hours, the first pencil of direct sunlight shone through the roof-box and along the passage to reach across the tomb chamber floor as far as the front edge of the basin stone in the end recess. As the thin line of light widened to a 17 cm-band and swung across the chamber floor, the tomb was dramatically illuminated and various details of the side and end recesses could be clearly seen in the light reflected from the floor. At 9.09 hours, the 17 cm-band of light began to narrow again and at exactly 9.15 hours, the direct beam was cut off from the tomb. For 17 minutes, therefore, at sunrise on the shortest day of the year, direct sunlight can enter Newgrange...
O'Kelly, Michael J., and Claire O'Kelly. Newgrange: Archaeology, Art, and Legend.
I would like to have very exact figures, such as the width of the beam of light every 5 seconds, as well as the position of the light on the walls and floor. But these figures are not available. However, with the figures we do have, we can do a rough estimate of the rate of the sunlight's movement.
am guessing that the light spread from an original 4cm to 40cm at
its maximum (the estimated original maximum as computed by J.
Partick). Then according to O'Kelly, it took 11 minutes from the
first pencil of light to reach the maximum width.
So: Widening of light = 40cm - 4cm = 36cm or 360mm
Time it took to widen = 11 minutes = 660 seconds
So the movement of the light grew at this rate: 360mm/660 sec. = or about .5mm every second or about 3cm per minute (a little more than 1 inch per minute).
This means that the movement of the light was significantly magnified, enough to study it and to use that information to make a determination about the day of the winter solstice. The above refers only to the widening of the light and not the movement of the band of light from one side of the passage to the other -- which I do not have any data for, but which would be an additional indicator for this instrument. I believe that with this kind of magnification, it would be possible to make fine distinctions that could pinpoint the actual day of the solstice in real-time -- if the sky was clear.
magnified display of the sun's movement is possible with large
structures and the figure of .5mm per second is consistent with
another large sundial, the Giant Sundial of Jantar Mantar in Jaipur,
One supposition that emerges from these studies of monuments incorporating astronomical alignments is that many of them became “special” when the astronomical body in question appeared at the appointed place. At these times, their sacred power was surely reinforced. Another way in which a similar effect could be achieved -- creating a very considerable visual impact at certain special times -- was through the interplay of sunlight and shadow.. A famous example occurs at the passage tomb of NEWGRANGE in Ireland.
What was the purpose and meaning of such hierophanies (ED: meaning "to bring to light the sacred" from the Greek]? By carefully placing rock art designs, sunlight could be made to play across them at certain times, with impressive effect. The Luiseño [ED: a California Indian tribe], for example, had an intense ceremonialism, a rich sky lore, and a calendar regulated by various astronomical observations. Although their seasonal calendar was lunarbased, they observed and celebrated the solstices, attaching particular importance to the winter solstice, which they regarded as a time of cosmological crisis.
Dr. Clive Ruggles, (Professor of Archaeoastronomy), Ancient Astronomy: An Encyclopedia of Cosmologies and Myth
"Today the first light enters about four minutes after sunrise, but calculations based on the precession of the Earth show that 5,000 years ago, first light would have entered exactly at sunrise."
Document of the US space agency NASA. http://spacemath.gsfc.nasa.gov/SED11/P8Newgrange.pdf
First, the roof-box is an anomalous feature without any obvious function in utilitarian terms (as it seems to us). Second, if the gap in the roof-box were merely 20 cm [8 inches] lower or higher, or the [lower] passage a few metres [10 feet] shorter or longer, then sunlight would never have entered the chamber.
Dr. Clive Ruggles, Astronomy in Prehistoric Britain and Ireland Astronomy in Prehistoric Britain and Ireland
Speaking of the original alignment 5000 years ago:
Originally, the beam would have struck the rear chamber orthostat (C8) and, possibly, would have been reflected onto another chamber stone, C10, which contains the famous triple spiral.
Anthony Murphy, quoted from a lecture to Astronomy Ireland in January 2002
The Ancient-Wisdom website in the UK made this comment:
The Light-box/Roof-box - Above the entrance passage is a 'light-box', which precisely aligns with the rising sun at the winter solstice of 21st December, so that the rays touch the ground at the very centre of the tomb... Many of the upright stones along the walls of the 19m (62ft) passage, which follows the rise of the hill, are richly decorated.
A researcher who took photographs at Newgrange over a number of days surrounding the winter solstice has this to say:
I noticed from my photographs that it [ED: the shaft of light] was in a different position each day. As the solstice approached the beam of light seemed to penetrate further each day, beginning on the left and ending on the right. However after the solstice the beam withdrew from the furthest point of entry and penetrated the central chamber less each day until it eventually failed to enter the central chamber at all.
Tim O'Brien also said:
"The construction features of Newgrange provide the ideal environment in which to study the minute movement of the sun when it is at visual standstill."
Writing about another but related Loughcrew Neolithic passage tomb in Ireland:
"As the sun shines directly onto the symbols engraved on the backstone they act not just as primitive representations of the sun, but as devices precisely positioned to measure solar movement."
Dr. Kate Prendergast made this point about its precision:
Further research has demonstrated just how precise this alignment is. Patrick (1974) has proved that the winter solstice orientation was operative when Newgrange was constructed, and therefore is an original, central and permanent feature of the monument. O’ Brien (1988) has shown that the chamber and passage are sophisticated and complex constructions, designed to maximize the accuracy and length of the beam of light coming into the chamber. His research indicates that at the time of construction, the beam of light entering the passage at Newgrange was so precisely framed by the roof-box that it could be used to calculate the day of the solstice itself. In short, Newgrange was precisely aligned on the winter solstice rising sun in such a way it could be used as a ‘clock’ to calculate the exact moment of the solstice. [ED: My emphasis]
Dr. Kate Prendergast, The Neolithic Monument of Newgrange in Ireland: A Cosmic Womb?
I believe this device could have determined the day of the solstice even during cloudy periods, and when the sky was clear, it might have been able to pinpoint the day of the solstice in real-time. Since the weather in Ireland is unpredictable, the Neolithic Newgrange astronomers, nevertheless, would have been able to determine the specific day of the winter solstice even if it was cloudy or rainy. They could do this by noticing the pattern of light on clear days before and after the solstice when the light was advancing and receding. Then they could make a determination by interpolating, a method very similar to that of the Romans who, as I have said, calculated the actual day of the solstice after the fact by making a number of observations followed by interpolation.
O'Kelly has remarked that in the years since he discovered the Newgrange solstice alignment, there has always been at least one clear day during the period surrounding the solstice. (O'Kelly, Michael J., and Claire O'Kelly. Newgrange: Archaeology, Art, and Legend)
However, when the sun was out and the days were clear, I believe that it was possible for the astronomers at Newgrange to determine the day of the solstice in real-time, something which was not possible for the Romans or the Greeks.
we can view the Newgrange structure and winter solstice alignment
as an instrument, then we can say the following:
at sunrise near the time of the solstice was at first restricted to
a narrow beam that went down a narrow hallway where it spread out,
but in a controlled manner. This 'device' was very much like a
magnifier that could enlarge and exaggerate the movement of the sun
at a time when detecting movement was particularly difficult.
Everyday the angle of the light changed along
the walls and floor, and the light advanced further or retreated.
It is, therefore, possible that Neolithic astronomers could have made a determination about the day of the solstice with the following data their instrument had gathered: the entry point of the light, the length of time the light shown, the angle and amount of the light on the walls and floor, the width of the light, the rate at which the beam of light widened and contracted and possibly the quality of the light and shadows on the deeply grooved triple spiral stone and other stone carvings.
This Neolithic instrument at the Newgrange passage tomb in Ireland, that
was designed to measure the sun's movement around the time of the
winter solstice, was possibly equal to or superior to ancient Greek
or Roman methods of measuring the day of the winter solstice.
It seems possible that the Newgrange instrument could determine the exact day of the solstice:
Today it might be possible with computer simulations to test out these hypotheses. Hopefully in the future, this will be done.
These sundials demonstrate that with the right construction and design,
can be extremely accurate.