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For those who have been gathering over the centuries at Stonehenge – the famous prehistoric monument that dominated Salisbury plain in south-west England for around 4,500 years – it was probably clear how the sun could guide its design.
The central axis of the stone circle was, and still is, aligned with the midsummer sunrise and midwinter sunset, with the stones largely shaping the rising and setting of the sun when the days were at their longest and shortest days.
But do Stonehenge and other megalithic monuments around the world also align with the moon?
The idea that Stonehenge was somehow connected to the moon emerged in the 1960s. However, the concept has not been systematically explored, said Clive Ruggles, emeritus professor of archeology in the school of archeology and ancient history at the University of Leicester.
This summer, archaeologists are using a little-known lunar phenomenon that occurs every 18.6 years to investigate as part of their work to understand why Stonehenge was built.
Moon position
Like the sun, the moon rises in the east and sets in the west. However, the moonrise and moonset move from north to south and back again in a month. The northern and southern extremes also change over a period of about 18 and a half years. The position of the moon is when the moonrise is furthest north and the moonset is farthest south.
“The rising of the moon changes every day and if you track this for a month you will notice that there is a north and south boundary where the moon never rises (or sets),” said Fabio Silva, senior lecturer in archaeological modeling at Bournemouth. University by email.
“If you were to look at these boundaries over 19 years you would notice that they change like an accordion: they expand up to an upper limit (the major lunar phase) and then begin to contract up to a lower limit (the minor lunar phase).”
This major lunar solstice is expected to occur in January 2025, but from now until mid-2025, the moon may appear to the casual observer as unusually low and high in the night sky during the month the moon.
“If you’re in one of those 19 years, then occasionally, you’ll see the moon rise or set much further north or south than it does most of the time. In the years in between you never see him there,” Ruggles said.
Despite the name of the phenomenon, the moon is not standing still in this period, he said.
“What’s still there are these limits, and when that happens is January of next year,” Ruggles added. “But for a year on both sides, if you happen to catch the rise of the moon at the right time, you will see the moon rising exceptionally low (in the sky).
There are two types of stone in Stonehenge: larger sarsen stones and smaller blue stones that form two concentric circles. Ruggles said that Stonehenge’s station stones, which form a rectangle around the circle, roughly align with the extreme positions of the moon during the lunar standstill.
How this lunar alignment was achieved, whether it was by design and its possible purpose are matters of debate that the team wishes to investigate.
Exploring the celestial connections of Stonehenge
Although there are no written documents that provide insight into the meaning and significance of Stonehenge, archaeologists have long believed that its solar alignments were intentional. Such alignments have been recognized in many parts of the world and would have been relatively easy for ancient builders to identify, given that knowledge of the annual cycle of the sun and its connection to the seasons would have been essential to occupation.
However, it is much more difficult to say whether Stonehenge is really related to the position of the moon.
“I don’t think we can say definitively, but to me, there are some pieces of evidence that made me think it was intentional,” Ruggles said.
One clue was the fact that archaeologists found cremated human remains clustered in the southeast, near where the southernmost moonrise will occur.
“I think it’s possible that they were aware of that direction of the moon and then it became some kind of sacred guidance,” 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 rising and setting of the moon at key moments when the moon aligns with the stones of the station. 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 around the year, with the moon at the right place at different phases each month,” Silva said in an April news release.
The team wants to understand what light and shadow patterns the moon creates at Stonehenge and whether they were meaningful to the people who built and used the monument.
Other monuments with a possible lunar connection
Stonehenge is not the only megalithic monument that may be linked to the moonstand.
In the United States, Erica Ellingson, professor emeritus of astrophysics at the University of Colorado Boulder, is investigating lunar alignments at Chimney Rock, a rocky ridge about 1,000 feet above a valley floor in Colorado. The landmark features two large pillar-like rocks that frame the skyline.
Between the years 900 and 1150, the ancestors of the Pueblo people built multistory buildings and ritual spaces on this hard-to-reach high ground with its dramatic view, Ellington said, and it remains an important site for the 26 Native American groups. who have traditional or cultural ties to the area.
“The extraordinary view of the sky between the two pinnae suggests an astronomical connection, but the gap is too far north for the Sun to shine through. However, the Moon can be seen rising there when it is close to its northernmost position, during the fixed lunar season,” she said via email.
Further evidence of moonwatching comes from tree-ring dating of wooden beams in the nearby ancient buildings, indicating their construction is related to moonstand dates of nearly 1,000 years ago, she said.
The Chalais Standing Stones, located on the Isle of Lewis in Scotland and built before Stonehenge, may be related to the moonstand, Ruggles said.
Bradley Schaefer, professor emeritus in the Department of Physics and Astronomy at Louisiana State University, said it is highly doubtful that ancient people were aware of the moon’s indeterminacy and built monuments aligned with it. More likely, he suggested, it was a coincidence.
“Each ancient site has thousands and hundreds of possible lines of sight, and one or more will always point somewhere near one of the 8 non-site directions,” he said via email.
The moon is difficult to identify for the casual observer, he said, and is only really visible in detailed observations of moonrise and moonset.
Although the moon’s position is a subtle change and historical records documenting the moon’s position are rare and difficult to interpret, Ellington said she thinks the connection is plausible because many ancient people watched the sky very closely.
“A moon watcher would see the moon rising or setting outside these boundaries, moving further and further out of bounds as the new moon approached,” she said.
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