A rare lunar event may reveal Stonehenge’s connection to the moon

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For those who have been gathering for centuries at Stonehenge – an impressive prehistoric monument that has dominated the Salisbury Plain in south-west England for about 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 sunrise in summer and sunset in winter, the stones dramatically framing the rising and setting suns when the days were longest and shortest.

But are Stonehenge and potentially other megalithic monuments around the world also aligned with the Moon?

The idea that Stonehenge was somehow connected to the moon gained ground in the 1960s. But the concept has not been systematically explored, said Clive Ruggles, emeritus professor of archaeoastronomy at the University of Leicester’s School of Archeology and Ancient History.

This summer, archaeologists are using a little-known lunar phenomenon that happens every 18.6 years to investigate why Stonehenge was built as part of their work.

Lunar calm

Like the sun, the moon rises in the east and sets in the west. However, the rising and setting of the Moon will move from north to south and back again during the month. In a period of about 18 and a half years, the northern and southern extremes also change. Lunar lunation occurs when the Moon’s northernmost and southernmost sunrise and sunset are the furthest apart.

“The rise of the moon changes every day and if you follow it on the moon you will notice that there is a northern and southern boundary beyond which the moon never rises (or sets),” said Fabio Silva, Associate Professor of Archaeological Modeling at Bournemouth. University via email.

“If you were to look at these limits over 19 years, you would notice that they change like an accordion: they widen up to the maximum limit (major monthly stop) and then begin to contract to the minimum limit (minor monthly stop). .”

This grand lunar standstill is due in January 2025, but from now until mid-2025, the Moon may appear unusually low and high to the casual observer in the night sky during the lunar month.

“If you’re in one of those 19 years, then from time to time you’ll see the moon rise or set much further north or south than it usually does.” You never see it there in the years in between,” Ruggles said.

Despite the phenomenon’s name, the moon doesn’t actually stand still during this period, he said.

“What stands in place are these limits, and the moment that happens is next January,” Ruggles added. “But for about a year on either side, if you happen to catch the moonrise at the right time, you’ll see the moon rise exceptionally low (in the sky).”

Stonehenge is made of two types of stone: the larger sarsen stones and the smaller bluestones, which form two concentric circles. Ruggles said the stones of Stonehenge, which form a rectangle around a circle, are roughly aligned with the extreme positions of the moon during the lunation.

How this lunar alignment was achieved, whether it was intentional, and its potential purpose are topics of debate that the team wants to explore.

Although there are no written documents that clarify the meaning and 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 the ancient builders to identify, given that knowledge of the annual cycle of the Sun and its connection to the seasons would have been essential for subsistence.

However, it is much more difficult to say whether Stonehenge is actually related to a lunar standstill.

“I don’t think we can say definitively, but to me there is some evidence that makes 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 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, which manages the site, have been documenting the rising and setting of the moon at key moments when the moon is in occultation with the station rocks. The moon was expected to align with the rectangle of the station rock 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 in the right place at different phases each month,” Silva said in an April news release.

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 is not the only megalithic monument potentially linked to a lunar standstill.

In the United States, Erica Ellingson, professor emeritus of astrophysics at the University of Colorado Boulder, studies the alignment of the moon at Chimney Rock, a rocky ridge about 1,000 feet above a valley floor in Colorado. The dominant feature is two large columnar rocks that frame the horizon.

Between 900 and 1150, the ancestors of the Pueblo people built multistory buildings and ritual spaces on this hard-to-reach high ground with a dramatic view, Ellington said, which remains an important site for 26 Native American groups. which have traditional or cultural ties to the area.

“The extraordinary view of the sky between the two peaks suggests an astronomical connection, but the gap is too far north for the Sun to ever shine through.” However, the moon may rise there when it approaches its most extreme northern position, during the main lunar quiescent season,” she said by email.

Further evidence of moon sightings comes from the dating of tree rings in nearby ancient buildings, which suggests their construction is linked to the dates of the lunar standstill nearly 1,000 years ago, she added.

The standing stones of Calanais, 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 standstill and built monuments in accordance with it. Rather, he suggested it was a coincidence.

“Each ancient site has tens to hundreds of potential lines of sight, and one or more will always point somewhere near one of the 8 repose directions,” he said by email.

Lunar quiescence is hard to spot for the casual moon watcher, he added, and is only really visible in detailed moonrise and moonset observations.

While the shift in the moon’s position is subtle and historical records documenting a lunar standstill are rare and difficult to interpret, Ellington said she thinks the connection is likely because many ancient people watched the sky very closely.

“A moon watcher would see the moon begin to rise or set outside of these limits and move further and further out of bounds as major lunar stasis approaches,” she said.