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For those gathered over the centuries at Stonehenge – the imposing prehistoric monument that has dominated the Salisbury Plain in south-west England for some 4,500 years – it was probably clear how the sun could have shaped its design.
The central axis of the stone circle was, and still is, aligned with the sunrise during midsummer and sunset during midwinter, with the stones dramatically framing the rising and setting sun when the days are at their longest and shortest.
But do Stonehenge and possibly other megalithic monuments around the world also correspond to the moon?
The idea that Stonehenge was somehow connected to the moon gained ground in the 1960s. However, the concept had not been systematically explored, says Clive Ruggles, emeritus professor of archaeoastronomy at 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.
Lunar standstill
Like the sun, the moon rises in the east and sets in the west. However, the moon’s rise and set move from north to south and back again within a month. The northern and southern extremes also change over a period of about 18.5 years. A lunar standstill occurs when the northernmost and southernmost moonrise and moonset are furthest apart.
“The rise of the moon changes every day and if you keep track of this for a month you will notice that there is a northern and a southern boundary beyond which the moon never rises (or sets),” says Fabio Silva, senior lecturer in archaeological modeling at Bournemouth. University via email.
“If you were to look at these limits over a period of 19 years, you would notice that they change like an accordion: they expand to a maximum limit (the major lunar standstill) and then begin to contract to a minimum limit (the minor lunar standstill) . .”
This major lunar standstill will occur in January 2025, but from now until mid-2025 it may appear to a casual observer as if the moon is unusually low and high in the night sky during the lunar month.
“If you are in one of those 19 years, from time to time you will see the moon rise or set much further north or south than is usually the case. In the intervening years you never see it there,” Ruggles said.
Despite the phenomenon’s name, the moon doesn’t actually stand still during this period, he said.
“What stands still are these borders, and the time when that happens is January of next year,” Ruggles added. “But if you see the moon rising at the right time, you will see the moon rise exceptionally low (in the sky) for about a year.”
Stonehenge is made of two types of stone: larger sarsen stones and smaller bluestones that form two concentric circles. Ruggles said Stonehenge’s station stones, which form a rectangle around the circle, roughly align with the moon’s extreme positions during the lunar standstill.
How this moon alignment was achieved, whether it was by design, and its potential purpose are topics of debate that the team plans to explore.
Investigating Stonehenge’s celestial connections
Although there are no written documents that shed light on the significance of Stonehenge, archaeologists have long believed that its alignment with the sun was intentional. Such alignments have been identified in many places around the world and would have been relatively easy for ancient builders to identify, as knowledge of the annual cycle of the sun and its relationship to the seasons would have been essential to subsistence.
However, it is much more difficult to say whether Stonehenge is really related to the lunar standstill.
“I don’t think we can say for sure, but to me there is some evidence that made me think it was intentional,” Ruggles said.
One clue was the fact that archaeologists found cremated human remains in the southeast, near where the southernmost moonrise will occur.
“I think there’s a possibility that they were aware of that direction of the moon and then that 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 moon’s rise and set at key moments when the moon aligns with the station stones. The moon was expected to align with the station stone rectangle twice a month between February 2024 and November 2025, Silva said.
“This will happen at different times of the day and night throughout the year, with the moon in different phases each month,” Silva said in a press release in April.
The team wants to understand what patterns of light and shadow the moon creates at Stonehenge and whether these might have had significance for the people who built and used the monument.
Other monuments with possible lunar link
Stonehenge isn’t the only megalithic monument possibly linked to the lunar standstill.
In the United States, Erica Ellingson, professor emeritus of astrophysics at the University of Colorado Boulder, examines the moon’s alignment at Chimney Rock, a rocky ridge about 1,000 feet above a valley in Colorado. The monument consists of two large pillar-like rocks that frame the horizon.
Between the 900s and 1150s, the ancestors of the Pueblo people built multi-story buildings and ritual spaces on this difficult-to-access high site, with its dramatic view, Ellington said, and it remains an important site for the 26 Native American groups. that have traditional or cultural ties with the area.
“The extraordinary view of the sky between the two pinnacles suggests an astronomical connection, but the opening is a little too far north for the sun to ever shine through. However, you can see the moon rising there when it is close to its northernmost position, during the great lunar standstill season,” she said via email.
Further evidence of moon watching comes from the dating of wooden beams in the nearby ancient buildings, indicating that their construction is linked to the dates of lunar standstill nearly 1,000 years ago, they added.
The Calanais Standing Stones, located on the Isle of Lewis in Scotland and built before Stonehenge, may also have a connection with the lunar standstill, Ruggles said.
Bradley Schaefer, professor emeritus of physics and astronomy at Louisiana State University, said he was deeply skeptical that ancient people were aware of the moon’s standstill and built monuments aligned with it. More likely, he suggested, it was a coincidence.
“Each ancient site has dozens to hundreds of potential sightlines, and one or more will always point somewhere near one of the eight standstill directions,” he said via email.
The lunar standstill is difficult to spot for a casual observer of the moon, he added, and is only really visible in detailed data on observations of the moon’s rise and set.
Although the shift in the moon’s position is subtle and historical records documenting the lunar standstill are rare and difficult to interpret, Ellington thinks she finds the connection plausible because many ancient people watched the sky very closely.
“A lunar observer would have seen the moon begin to rise or set outside these boundaries, moving further and further outside the boundaries as the great lunar standstill approached,” she said.
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