(NewsNation) — Skywatchers could gain new insights about Stonehenge during a rare celestial event coming to the skies this summer solstice on Friday, June 21.

Every midsummer’s night, tens of thousands of people gather at Stonehenge to celebrate and witness the rising sun in alignment with the Heel Stone standing outside the circle, but a longstanding hypothesis is that part of the historic structure is also aligned with the moonrise and moonset at what is called a major lunar standstill.

A major lunar standstill happens every 18.6 years when the moon rises and sets at its most extreme points on the horizon while also climbing to its highest and lowest points in the sky, making it appear in the night sky longer.

This year marks the first “major lunar standstill,” also known as a “lunistice,” since 2006. During the event, the tilts of both the Earth and the moon are at their maximum and will overlap with the summer solstice on Friday night in the northern hemisphere.

Similar spectacles linked to Indigenous landmarks in the U.S. will be occurring across these lunistice months at Chimney Rock in Colorado, the Hopewell Sites in Ohio and Chaco Canyon in New Mexico.

Local high points of the major lunar standstill will vary based on location and weather conditions, but it has a chance of visibility two nights a month from now until November 2025.

While the solar system is essentially flat, and the majority of planets and asteroids orbit within a flat plane or disk called the ecliptic, the moon’s orbit comes from a slightly different angle.

As the Earth spins along an axis tilted by 23.4 degrees off this ecliptic plane, our moon’s orbit is tilted by only 5.1 degrees relative to the ecliptic.

The result is that the moon’s rising and setting points, and thus how much of the Earth it traverses in between, can vary by as much as 57 degrees depending on the year.

According to English Heritage, the long axis of the rectangle formed by Stonehenge’s four Station Stones orients to the direction of the southernmost moonrise at the major lunar standstill.

“Stonehenge’s architectural connection to the Sun is well known, but its link with the moon is less well understood,” said Clive Ruggles, emeritus professor of archaeoastronomy at Leicester University. “The four Station Stones align with the moon’s extreme positions, and researchers have debated for years whether this was deliberate, and—if so—how this was achieved and what might have been its purpose.”

Scientists will be at Stonehenge throughout the “standstill season” to photograph the moments when the moon is in alignment with the Station Stones.

“Unlike the Sun, tracking the Moon’s extremes isn’t straightforward, requiring specific timing and weather conditions,” said Dr. Amanda Chadburn at the University of Oxford’s Kellogg College. “We want to understand something of what it was like to experience these extreme moonrises and sets and to witness their visual effects on the stones—for example, patterns of light and shadow—and consider modern influences like traffic and trees, and to document all of this through photography for future study.”