Archaeoastronomy and Stonehenge - AbsoluteAstronomy.com

The prehistoric monument of Stonehenge

Stonehenge

Stonehenge is a prehistoric monument located in the English county of Wiltshire, about west of Amesbury and north of Salisbury. One of the most famous sites in the world, Stonehenge is composed of a circular setting of large standing stones set within earthworks...

has long been studied for its possible connections with ancient astronomy. Archaeoastronomers

Archaeoastronomy

Archaeoastronomy is the study of how people in the past "have understood the phenomena in the sky how they used phenomena in the sky and what role the sky played in their cultures." Clive Ruggles argues it is misleading to consider archaeoastronomy to be the study of ancient astronomy, as modern...

have claimed that Stonehenge represents an "ancient observatory," although the extent of its use for that purpose is in dispute. Many also believe that the site may have had astrological/spiritual

Spirituality

Spirituality can refer to an ultimate or an alleged immaterial reality; an inner path enabling a person to discover the essence of his/her being; or the “deepest values and meanings by which people live.” Spiritual practices, including meditation, prayer and contemplation, are intended to develop...

significance attached to it as well.

The discovery of evidence for a neighbour to the Heel Stone has challenged the interpretation of it as a midsummer sunrise marker. The second stone may have instead been one side of a 'solar corridor' used to frame the sunrise.

Early work

Stonehenge features an opening in the henge earthwork facing northeast, and suggestions that particular significance was placed by its builders on the solstice

Solstice

A solstice is an astronomical event that happens twice each year when the Sun's apparent position in the sky, as viewed from Earth, reaches its northernmost or southernmost extremes...

and equinox

Equinox

An equinox occurs twice a year, when the tilt of the Earth's axis is inclined neither away from nor towards the Sun, the center of the Sun being in the same plane as the Earth's equator...

points have followed. For example, the summer solstice sun rose close to the Heel Stone, and the sun's first rays shone into the centre of the monument between the horseshoe arrangement. While it is possible that such an alignment can be coincidental, this astronomical orientation had been acknowledged since William Stukeley

William Stukeley

William Stukeley FRS, FRCP, FSA was an English antiquarian who pioneered the archaeological investigation of the prehistoric monuments of Stonehenge and Avebury, work for which he has been remembered as "probably... the most important of the early forerunners of the discipline of archaeology"...

drew the site and first identified its axis along the midsummer sunrise in 1720.

Stukeley noticed that the Heel Stone was not precisely aligned on the sunrise. Year to year, the movement of the sun across the sky appears regular. However, due to temporal changes in obliquity of the ecliptic, illumination declinations change with time. The purported Heel Stone alignment with summer solstice sunrise would have been less accurate four to five thousand years ago. The Heel Stone, in fact, is located at 1/7 of circumference from due North, as noted by archaeologist James Q. Jacobs. Stukeley and the renowned astronomer Edmund Halley were to attempt what amounted to the first scientific attempt to date a prehistoric monument. Stukeley concluded the Stonehenge had been set up "by the use of a magnetic compass to lay out the works, the needle varying so much, at that time, from true north." He attempted to calculate the change in magnetic variation between the observed and theoretical (ideal) Stonehenge sunrise, which he imagined would relate to the date of construction. Their calculations returned three dates, the earliest of which, 460 BC, was accepted by Stukeley. That was incorrect, but this early exercise in dating is a landmark in field archaeology.

Early efforts to date Stonehenge exploited tiny changes in astronomical alignments and led to efforts such as H Broome's 1864 theory that the monument was built in 977 BC, when the star Sirius

Sirius

Sirius is the brightest star in the night sky. With a visual apparent magnitude of −1.46, it is almost twice as bright as Canopus, the next brightest star. The name "Sirius" is derived from the Ancient Greek: Seirios . The star has the Bayer designation Alpha Canis Majoris...

would have risen over Stonehenge's Avenue

Avenue (archaeology)

British Archaeologists refine the general archaeological use of avenue to denote a long, parallel-sided strip of land, measuring up to about 30m in width, open at either end and with edges marked by stone or timber alignments and/or a low earth bank and ditch...

. Sir Norman Lockyer proposed a date of 1680 BC based entirely on an incorrect sunrise azimuth for the Avenue, aligning it on a nearby Ordnance Survey

Ordnance Survey

Ordnance Survey , an executive agency and non-ministerial government department of the Government of the United Kingdom, is the national mapping agency for Great Britain, producing maps of Great Britain , and one of the world's largest producers of maps.The name reflects its creation together with...

trig point

Trig point

A triangulation station, also known as a triangulation pillar, trigonometrical station, trigonometrical point, trig station, trig beacon or trig point, and sometimes informally as a trig, is a fixed surveying station, used in geodetic surveying and other surveying projects in its vicinity...

, a modern feature. Petrie preferred a later date of AD 730. The necessary stones were leaning considerably during his survey, and it was not considered accurate.

An archaeoastronomy debate was triggered by the 1963 publication of Stonehenge Decoded, by British-born astronomer Gerald Hawkins

Gerald Hawkins

Gerald Stanley Hawkins was an English astronomer and author most famous for his work in the field of archaeoastronomy. A professor and chair of the astronomy department at Boston University in the United States...

. Hawkins claimed to observe numerous alignments, both lunar and solar. He argued that Stonehenge could have been used to predict eclipses. Hawkins' book received wide publicity, in part because he used a computer in his calculations, then a rarity. Archaeologists were suspicious in the face of further contributions to the debate coming from British astronomer C. A. 'Peter' Newham and Sir Fred Hoyle

Fred Hoyle

Sir Fred Hoyle FRS was an English astronomer and mathematician noted primarily for his contribution to the theory of stellar nucleosynthesis and his often controversial stance on other cosmological and scientific matters—in particular his rejection of the "Big Bang" theory, a term originally...

, the famous Cambridge cosmologist, as well as by Alexander Thom

Alexander Thom

Alexander "Sandy" Thom was a Scottish engineer most famous for his theory of the Megalithic yard, categorization of stone circles and his studies of Stonehenge and other archaeological sites.- Life and work :...

, a retired professor of engineering, who had been studying stone circles for more than 20 years. Their theories have faced criticism in recent decades from Richard J. C. Atkinson

Richard J. C. Atkinson

Richard John Copland Atkinson CBE was a British prehistorian and archaeologist.-Biography:He was born in Evershot, Dorset and went to Sherborne School and then Magdalen College, Oxford, reading PPE...

and others who have suggested impracticalities in the 'Stone Age calculator' interpretive approach.

Newham and the Station Stones

Newham had found an alignment for the equinoxes by drawing a line between one of the Station Stones with a posthole next to the Heel Stone. Moving away from the sun, he also identified a lunar alignment; the long sides of the rectangle created by the four station stones matched the moon rise and moonset at the major standstill.

Two of the Station Stones are damaged and although their positions would create an approximate rectangle, their date and thus their relationship with the other features at the site is uncertain. Stonehenge's latitude is unusual in that only at this approximate latitude (within about 50 km) do the lunar and solar events above occur at right angles to one another. More than 50 km north or south of the latitude

Latitude

In geography, the latitude of a location on the Earth is the angular distance of that location south or north of the Equator. The latitude is an angle, and is usually measured in degrees . The equator has a latitude of 0°, the North pole has a latitude of 90° north , and the South pole has a...

of Stonehenge, the station stones would have to be set out as a parallelogram

Parallelogram

In Euclidean geometry, a parallelogram is a convex quadrilateral with two pairs of parallel sides. The opposite or facing sides of a parallelogram are of equal length and the opposite angles of a parallelogram are of equal measure...

Gerald Hawkins' work

Gerald Hawkins' work on Stonehenge was first published in Nature
Nature
Nature, in the broadest sense, is equivalent to the natural world, physical world, or material world. "Nature" refers to the phenomena of the physical world, and also to life in general...

in 1963 following analyses he had carried out using the Harvard-Smithsonian IBM computer. Hawkins found not one or two alignments but dozens. He had studied 165 significant features at the monument and used the computer to check every alignment between them against every rising and setting point for the sun, moon, planets, and bright stars in the positions they would have been in 1500 BC. Thirteen solar and eleven lunar correlations were very precise against the early features at the site with precision falling during the megalithic stages. Hawkins also proposed a method for using the Aubrey holes

Aubrey holes

The Aubrey holes are a ring of fifty-six Late Cretaceous Seaford Chalk pits at Stonehenge named after the seventeenth-century antiquarian John Aubrey. They date to the earliest phases of Stonehenge in the late fourth and early third millennium BC...

to predict lunar eclipses by moving markers from hole to hole. In 1965 Hawkins wrote (with J. B. White) Stonehenge Decoded, which detailed his findings and proposed that the monument was a 'Neolithic computer'.

Atkinson replied with his article "Moonshine on Stonehenge" in Antiquity
Antiquity (journal)
Antiquity is an academic journal dedicated to the subject of archaeology. It publishes four editions a year, covering topics worldwide from all periods. Its current editor is Martin Carver, Emeritus Professor of Archaeology at the University of York....

in 1966, pointing out that some of the pits which Hawkins had used for his sight lines were more likely to have been natural depressions, and that he had allowed a margin of error of up to 2 degrees in his alignments. Atkinson found that the probability of so many alignments being visible from 165 points to be close to 0.5 (or rather 50:50) rather that the "one in a million" possibility which Hawkins had claimed. That the Station Stones stood on top of the earlier Aubrey Holes meant that many of Hawkins' alignments between the two features were illusory. The same article by Atkinson contains further criticisms of the interpretation of Aubrey Holes

Aubrey holes

as astronomical markers, and of Fred Hoyle's work.

A question exists over whether the English climate would have permitted accurate observation of astronomical events. Modern researchers were looking for alignments with phenomena they already knew existed; the prehistoric users of the site did not have this advantage.

Alexander Thom's work

Alexander Thom

had been examining stone circles since the 1950s in search of astronomical alignments and the megalithic yard

Megalithic Yard

A Megalithic Yard is a unit of measurement, about , that some researchers believe was used in the construction of megalithic structures. The proposal was made by Alexander Thom as a result of his surveys of 600 megalithic sites in England, Scotland, Wales and Britanny...

. It was not until 1973 that he turned his attention to Stonehenge. Thom chose to ignore alignments between features within the monument, considering them to be too close together to be reliable. He looked for landscape features that could have marked lunar and solar events. However, one of Thom's key sites, Peter's Mound, turned out to be a twentieth-century rubbish dump.

Later theories

Although Stonehenge has become an increasingly popular destination during the summer solstice, with 20,000 people visiting in 2005, scholars have developed growing evidence that indicates prehistoric people visited the site only during the winter solstice. The only megalithic monuments in the British Isles to contain a clear, compelling solar alignment are Newgrange

Newgrange

Newgrange is a prehistoric monument located in County Meath, on the eastern side of Ireland, about one kilometre north of the River Boyne. It was built around 3200 BC , during the Neolithic period...

and Maeshowe

Maeshowe

Maeshowe is a Neolithic chambered cairn and passage grave situated on Mainland, Orkney, Scotland. The monuments around Maeshowe, including Skara Brae, were designated a UNESCO World Heritage Site in 1999. It gives its name to the Maeshowe type of chambered cairn, which is limited to Orkney...

, which both famously face the winter solstice sunrise.

The most recent such evidence supporting the theory of winter visits includes bones and teeth from pigs which were slaughtered at nearby Durrington Walls

Durrington Walls

Durrington Walls is the site of a large Neolithic settlement and later henge enclosure located in the Stonehenge World Heritage Site. It is 2 miles north-east of Stonehenge in the parish of Durrington, just north of Amesbury...

. Their age at death indicating that they were slaughtered either in December or January every year. Mike Parker Pearson of the University of Sheffield

University of Sheffield

The University of Sheffield is a research university based in the city of Sheffield in South Yorkshire, England. It is one of the original 'red brick' universities and is a member of the Russell Group of leading research intensive universities...

has said, "We have no evidence that anyone was in the landscape in summer."

External links

Temporal Epoch Calculations, An introduction to research considerations regarding temporal variations in archaeoastronomical and archaeogeodetic variables.