Astronomical Research at Stonehenge

Introduction

Stonehenge is often described as mysterious and impossible to understand. An example of this is that its relationship to the skies and heavenly bodies is often misunderstood, even sometimes by archaeologists. Perhaps this is because archaeoastronomy – the study of how ancient people understood phenomena in the sky and how they used this sky-knowledge in their cultures – is rarely taught in the UK. However, most archaeologists and indeed the general public are aware that there is a link between the summer solstice and Stonehenge, although many would be hard-pressed to elaborate further.

This combination of apparent mystery and a lack of detailed knowledge has led to some eye-watering claims about Stonehenge in the past: “it was a computer”, “it was built by aliens”, and so on. New studies of the landscape context of Stonehenge and a number of nearby monuments, and firming up the dates for these prehistoric structures, have cut through some of this confusion. They have established that certain monuments were designed to view heavenly bodies at certain times of the year.

This article is based on research in a lavishly illustrated new book by Ruggles and Chadburn, published by Liverpool University Press for Historic England on May 8th 2024. We would like to thank Historic England for commissioning and publishing the book, for providing our expert illustrator Sharon Soutar, and for funding the dating programme for Woodhenge. Wiltshire Museum kindly provided the material to do this.

Solar alignments at Stonehenge

In 1720, the antiquarian William Stukeley first noticed that the architecture of Stonehenge related to the sun, famously noting that the axis of the monument was aligned upon the midsummer sunrise. Looking the opposite way, one can see that the solar alignment also works in that direction, as the midwinter setting sun is also framed by the stones. Standing at a fixed point, the solstice suns always rise or set each year at exactly the same points in the landscape, a phenomenon visible for a few days around each solstice.

Stonehenge’s architecture was designed to allow views of the exact points where the summer and winter solstice suns appear or disappear on the horizon. It is a monument designed to sight the sun. Today, many archaeologists think that the winter solstice was the more important of the two solstices for its prehistoric builders, and this axis and view is now marked by a large metal arrow for visitors.

The moon and Stonehenge

As well as the sun, it is likely that the moon was also important to the builders of Stonehenge. The monument’s relationship to the moon, however, is much more difficult to prove. Unlike the sun which has an annual solstice, the moon’s ‘lunistice’ positions (reached every 27 days) themselves vary and are at their furthest apart in the landscape around every 19th year (a time known as the major lunar standstill).

A rectangle of much smaller stones known as the Station Stones is positioned outside the stone circle, near to the henge earthworks (see illustration above) and the long sides of the rectangle are broadly aligned with the most southerly moonrise and the most northerly moonset.

We believe that this was deliberate. It is currently the major lunar standstill season, so we are researching and observing the moon at Stonehenge during this critical time. It should be noted that the Station Stones rectangle is also aligned (along its short sides) with the solar axis which we have noted above.

Stonehenge and other astronomical monuments

Using computer modelling and field observations, our new research has established the exact positions of the rising and setting sun and moon positions in the landscape surrounding Stonehenge in prehistory, taking into account the slightly different position of the sun and moon in 2500 BC, the approximate date when the stones were erected at Stonehenge. This means we now know how far their views or sightlines stretched, which allows us to understand the prehistoric landscape rather better.

However, as well as Stonehenge, there are a number of other nearby monuments which precisely frame views of the sun at the solstices, including Woodhenge, the Southern Circle at Durrington Walls and a timber row at Lark Hill, and we have done similar calculations for them. It is clear that even distant horizons were important to the monument builders – the longest sightline is nearly 15 kilometres long (this is the view from Stonehenge to the most northerly moonset on the ridge at Gibbet Knoll, near Market Lavington).

Reconstructing ancient sun-sighting monuments in their landscapes

We have pulled together various data sets to precisely reconstruct astronomical views which are now impossible to see. One example is at Durrington Walls henge, where the remains of the Southern Circle timber monument within it are now buried meters below ground, partly under a huge road embankment. The view from the centre of the Southern Circle, out through its entrance posts and down its Avenue toward the rising winter solstice sun, has been digitally reconstructed here. Data from two excavations, one in the 1960s and one in 2005-2006, and terrain modelling and calculations of the sun’s position in 2500 BC have been combined to reconstruct this view with a high degree of accuracy.

Dating Woodhenge

Critical to our understanding of these astronomical monuments is the date at which they were built. Unlike Stonehenge, Woodhenge was not well dated, but there was plenty of excavated material suitable for a dating programme in Wiltshire Museum. Charcoal from the timber rings, excavated nearly 100 years ago by the archaeologist Maud Cunnington, and antler picks discovered in later excavations of the ditch were all used. The results show that the oval timber rings – the astronomical monument aligned on the sun – were erected around 2600 BC but that the surrounding henge earthworks were constructed around 200 years later. This perhaps explains why the henge entrance is not aligned with the sun, ie because the monument was no longer used for astronomical purposes.

Impact of the research

Further information

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