by Duncan  Lunan

The plane of the Earth’s orbit around the Sun is the Ecliptic, the center line of the Zodiac, and the Earth’s axis is inclined to it by 23.5 degrees;  as the Sun moves along the Ecliptic over the course of the year, its horizon position varies from its most southerly midwinter rise and set, when it’s overhead at the Tropic of Capricorn, to its most northerly midsummer rise and set, when it’s overhead at the Tropic of Cancer.  Those events are known as the  midwinter solstice and the midsummer solstice, respectively.  Although they are the shortest and longest days of the year in the northern hemisphere, it’s the opposite in the south, and because the Earth’s orbit is an ellipse and not a perfect circle, the latest winter sunrises and summer sunsets in our latitudes come after the solstices themselves.

Because the Earth’s orbit is not a perfect circle, and the length of the day doesn’t divide into the year, the dates of the solstices can vary by a day or two, year by year;  but this year the summer solstice is bang on its ‘usual’ date, June 21^st. 

Archaeologists argue nowadays about whether midsummer or midwinter was more important to the ancient builders of Stonehenge, but large crowds would normally be gathering there on June 21^st  – it’s much warmer then than at midwinter, to begin with.  Much is made of the fact that when the great sarsen stones were erected to form Stonehenge III, the largest ones were on the midwinter sunset side.  But the case for midsummer is still pretty strong. 

In his book “Stonehenge, the Story of a Sacred Landscape”  (Head of Zeus, 2016), archaeologist Francis Pryor rightly drew attention to the recent discovery of gullies northeast of Stonehenge, aligned with midsummer sunrise.  Though the gullies have been hidden by topsoil for thousands of years, they would have been highly visible in the early centuries after Ice Age, at the time around 8000 BC when the ‘Car Park Posts’, the oldest known features on the site, were erected.  Some commentators have reported the discovery as if it shows that the astronomical alignments at the site were coincidental, but the real point is that the significance of the gullies was recognised by people who already knew where midsummer sunrise was and what it meant.  The same alignment is marked by the Station Stones, which were positioned on the Stonehenge bank soon after it and the surrounding ditch were created, and is also marked by the first stage of the processional Avenue which leads northeast towards the older Stonehenge Cursus, and then south towards the river, where other stones were erected.

Whether that part of the Avenue was the beginning or the end of the processions isn’t crucial:  it may well have been both, at different times of the year, or even in different centuries.   But the Avenue does have the important feature of the Heelstone, over which the midsummer sun now rises.  The tilt of the Earth’s axis varies between 22 and 24 degrees on a 40,000-cycle, and when Stonehenge was built it was near maximum.  At that time, the midsummer Sun didn’t rise over the Heelstone as it does now, but beside it.  That gave me an important guide when I was planning the first astronomically aligned stone circle for over 3000 years, in Sighthill Park in Glasgow, in the Glasgow Parks Department Astronomy Project of 1978-79. Sighthill Stone Circle – An Update By Kenny Brophy – Urban Pre-historian.

I had decided that the structure would be built around midsummer sunrise, but what form was it to take?   In his book “The Bronze Age in Barbarian Europe”  (Routledge and Kegan Paul, 1979), Jacques Briard wrote,  “At that time there may have been great ceremonies, linked with a worship of the seasons and with agriculture…  The layout of the monument suggests a whole ritual:  the arrival in procession along the avenue, the crossing of the sacred ditch and the separation of the faithful into different areas, only the initiated, the officiators at the ceremony or perhaps the princes of Wessex as well, being allowed to pass under the giant trilithons.” 

But the layout doesn’t actually suit the ritual he describes.  The ditch and bank surrounding the circle go right up the Avenue, so it seems likely that everything within them was forbidden territory to the uninitiated.  If they were kept that far back, however, it would be very difficult to conduct a ceremony at the centre;  and even if they were allowed within the bank to surround the circle, relatively few would be able to see past the sarsens, bluestones and trilithons.  Only the very few right at the centre would actually see the event, the sunrise, in its intended relation to the structure, and that doesn’t make political sense in relation to the Apollo-type commitment of resources to building Stonehenge.  NASA had no intention of burdening the Apollo 11 astronauts with a TV camera until Congress insisted on it:  only one man could be first on the Moon, but the hundreds of thousands who worked for it, the millions who paid for it and the billions whom their leaders wanted to impress must all be able to see what happened.  Since ‘the princes of Wessex’ had no TV remotes their ceremony would have been a spectacle, out where everybody could see it.  Stones don’t conduct ceremonies, people do:  as I see it, the head man would have been on the centre line, beside the Heelstone, so that the Sun rose over him, and his shadow would be cast into the mysterious centre of the circle.  There was another stone there, at one time, but as we don’t know for sure when it was erected or taken down, I haven’t let it confuse the issue.

My circle on the high point of Sighthill Park would be only 40 feet across, and if I had a single privileged viewpoint, I was worried that people would be pushing and shoving to get into it.  Instead, I borrowed from the layout of observing sites which Prof. Alexander Thom had postulated around ‘Le Grand Menhir Brisé’, the huge broken monolith in Brittany, scaling down the layout from 20 miles across to 40 feet.  With the tops of the stones at adult eye level, as the Sun rose over the marker stone, everyone would be able to see its shadow fall on the central one, while the shadow of the central one fell on the midwinter sunset one  (though not exactly opposite).  In convincing the Parks Department and the Manpower Services Commission that I was right, I was greatly helped by a letter from Dr. Ed Krupp, of the Griffith Observatory in Los Angeles, independently making the same suggestion.

As regular readers know, in 2012 it was announced that Sighthill Park and the hill that it stood on would be removed to make way for new housing.  A public appeal which generated 6500 signatures led to the removal of the stones intact in 2016, along with the topsoil in which many people had scattered their loved ones’ ashes over the previous 37 years.  I was commissioned to find a new site, on the east end of the former park, and to recalculate the astronomical alignments.  The stones were re-erected there in 2018 and the public reopening was to have been at midsummer solstice in 2020, but has been postponed for obvious reasons – maybe to this year’s autumn equinox.  The topsoil has been replaced and the contents of the time capsule have been reburied in a new container, along with a matching one for the present day.

Attempts to photograph midsummer and equinox sunsets at the new site have been only partly successful, due to cloud.  But my colleague Gerry Cassidy and I will be trying again, weather permitting, and since the rising and setting positions of the Sun hardly change for a week either side of the solstice, we may have been successful by the time this article appears.  As of Thursday 17^th, the forecast for tomorrow morning looks sufficiently promising to make the attempt, so I may be able to update this and have photos to show in time for Sunday – failing that, maybe next Sunday, or the Sunday after  – watch this space!

Duncan Lunan has written several articles for The Orkney News which help those beginners in astronomy. Use our search option to find them. Here’s the latest: Astronomy for Beginners: Venus