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To all who have gathered over the centuries at Stonehenge – the most imposing prehistoric monument that exists dominated the plains of Salisbury in southwest England for around 4,500 years – it was probably clear how the sun might have influenced its design.
The central axis of the stone circle was and still is aligned with the sunrise in midsummer and the sunset in midwinter, with the stones dramatically framing the rising and setting of the sun when the days were at their longest and shortest.
But are Stonehenge, and possibly other megalithic monuments around the world, also based on the moon?
The idea that Stonehenge was somehow connected to the moon took hold in the 1960s. However, the concept has not yet been systematically researched, said Clive Ruggles, Emeritus Professor of Archaeoastronomy at the University of Leicester’s Faculty of Archeology and Ancient History.
This summer, as part of their work to understand the construction of Stonehenge, archaeologists are studying a little-known lunar phenomenon that occurs every 18.6 years.
lunar standstill
Like the sun, the moon rises in the east and sets in the west. However, moonrise and moonset move from north to south and back again within a month. The north and south extremes also change over a period of about 18.5 years. The lunar standstill occurs when the northernmost and southernmost moonrise and sunset are furthest apart.
“The moonrise changes every day and if you follow this for a month, you will notice that there is a northern and a southern boundary beyond which the moon never rises (or sets),” said Fabio Silva, lecturer in archaeology Modeling at Bournemouth University, via email.
“If you look at these boundaries over a period of 19 years, you would find that they change like an accordion: they expand to a maximum limit (the great lunar standstill) and then begin to expand to a minimum limit (the small lunar standstill). .”
This major lunar standstill is scheduled to occur in January 2025, but from now until mid-2025, the moon could appear unusually low and high in the night sky to a casual observer during the lunar month.
“If you are in any of these 19 years, you will, from time to time, see the moon rise or set much further north or south than it normally does. In the intervening years, you never see it there,” Ruggles said.
Despite the phenomenon’s name, the moon is not actually standing still during this time, he said.
“What stands still are these borders, and the moment when that happens is in January of next year,” Ruggles added. “But for about a year, if you catch the moonrise at the right time, you’ll see the moon rise exceptionally low (in the sky).”
Stonehenge is made up of two types of stone: larger sarsen stones and smaller bluestones, which form two concentric circles. Ruggles said Stonehenge’s station stones, which form a rectangle around the circle, are roughly aligned with the moon’s extreme positions during lunar standstill.
How this lunar alignment was achieved, whether it was intentional, and what possible purpose it served are topics of discussion the team plans to explore.
Although there are no written documents to shed light on the meaning and significance of Stonehenge, archaeologists have long assumed that its solar alignment was intentional. Such alignments have been identified in many locations around the world and would have been relatively easy for ancient builders to identify, as knowledge of the sun’s annual cycle and its connection to the seasons would have been vital to subsistence.
However, it is much more difficult to say whether Stonehenge actually has a connection to the lunar standstill.
“I don’t think we can say definitively, but to me there is some evidence that leads me to believe it was intentional,” Ruggles said.
One clue was the fact that archaeologists have found accumulated cremated human remains in the southeast, near the site where the southernmost moonrise will occur.
“I think there’s a possibility that they were aware of this direction of the moon and then it became some kind of sacred direction,” Ruggles said.
Since April, Ruggles and Silva, along with colleagues from Bournemouth University, the University of Oxford and English Heritage, the organization that manages the site, have been documenting the moonrise and moonset at key moments when the moon is in line with the station stones. The moon was expected to align with the station’s stone rectangle twice a month from about February 2024 to November 2025, Silva said.
“This will happen at different times of the day and night throughout the year, with the moon being in the right place at different phases each month,” Silva said in a news release in April.
The team wants to understand what patterns of light and shadow the moon creates at Stonehenge and whether they may have had meaning for the people who built and used the monument.
Stonehenge isn’t the only megalithic monument that may be linked to the lunar standstill.
In the United States, Erica Ellingson, professor emeritus of astrophysics at the University of Colorado Boulder, studies lunar alignments at Chimney Rock, a rocky ridge about 1,000 feet above a valley floor in Colorado. The landmark consists of two large pillar-like rocks that frame the horizon.
Between the years 900 and 1150, the ancestors of the Pueblo people built multistory buildings and ritual spaces on this difficult-to-access knoll with its dramatic views, Ellington said, and it remains an important site for the 26 Native American groups that have a traditional or cultural connection to the city have region.
“The extraordinary view of the sky between the two pinnacles suggests an astronomical connection, but the gap is a little too far north for the sun to ever shine through. However, the moon can be seen rising there as it approaches its northernmost position during the great lunar standstill period,” she said by email.
Further evidence of lunar observation includes tree-ring dating of wooden beams in the nearby ancient buildings, which suggests their construction is linked to the dates of the moon’s standstill nearly 1,000 years ago, she added.
The Calanais Standing Stones, located on the Isle of Lewis in Scotland and erected before Stonehenge, may also have a connection to the lunar standstill, Ruggles said.
Bradley Schaefer, professor emeritus in the department of physics and astronomy at Louisiana State University, said he is deeply skeptical that ancient people were aware of the moon’s stagnation and built monuments focused on it. More likely, he suspected, was a coincidence.
“Every ancient site has dozens to hundreds of potential sight lines, and one or more will always point somewhere near one of the eight still directions,” he said by email.
The lunar standstill is difficult to detect for a casual lunar observer, he added, and is only truly visible in detailed data on observations of moonrise and moonset.
Although the shift in the moon’s position is barely noticeable and historical records documenting the moon’s standstill are rare and difficult to interpret, Ellington said she believes the connection is plausible because many ancient peoples observed the sky very closely.
“A moon watcher would have seen the moon rising or setting outside of these boundaries and moving further and further outside the boundaries as the moon’s great standstill approached,” she said.