There's a problem all archaeoastronomers face when they're dealing with properly ancient sites and their possible alignments to the sky, and it's called the change in the Obliquity of the Ecliptic.
The Earth's rotational axis is currently tilted at an angle of roughly 23.4° to the plane of our orbit around the Sun - it's why we have seasons. This angle (the Obliquity of the Ecliptic) isn't fixed, it varies over long periods of time (roughly 41000 years) between about 22.1° and 24.5°.
This angle is critical in determining exactly where on the horizon the Sun rises and sets at the solstices - the greater the angle, the closer to the due north direction the summer solstice sunrise and set appear; and the closer to the due south direction the winter solstice sunrise and set are.
The large sarsens of Stonehenge were erected about 4,500 years ago when Earth's tilt was 24° (in round numbers), and at summer solstice the Sun rose and set about 1° further north than it does today. Similarly, the winter solstice Sun rose and set about 1° further south than today.
All this means is that we can't, today, experience the alignments at solstice exactly the same way as the people who built Stonehenge. Sure, we can do calculations to correct for the offset but we can't ever see what they saw. Frustrating.
The Moon's orbit is tilted to the plane of the Earth's by about 5.1° and the Moon's orbital path itself rotates around the Earth, taking 18.61 years to go around once. This is what gives rise to the so-called Major and Minor Lunar Standstills.
In the couple of years around the Major Lunar Standstills the Moon can rise and set much further around to the north and south than the Sun can ever reach - something like 10° or roughly 20 lunar diameters further at the utmost extremes. It's these extremes that the long sides of the Station Stone rectangle are aligned on, as first reported by Peter Newham (and, independently, Gerald Hawkins) in the 1960s.
We can take advantage of the phenomenon, because while the Moon is in the "Major" half of its cycle there are times when it can rise (and set) at the azimuths that the ancient Sun once did and no longer does.
So we can effectively use the Moon as a proxy for the ancient Sun.
As I've written about before, there is a secondary solstice axis that runs through Stonehenge which points towards the winter solstice sunrise in the SE and the summer solstice sunset in the NW.
There is a sightline, tightly constrained, through Stonehenge that frames the precise spot on the SE horizon where the ancient winter solstice Sun appeared. It makes use of a notch in Stone 58 and the edge of Stone 53 to create a "hole" where you can view this small patch of horizon.
Once upon a time, 4,500 years ago, someone standing here at winter solstice would see the Sun rise just to the left of the electricity pylon you can see in the image above. Due to the change in the Earth's tilt, as explained above, that doesn't happen for us today.
Happily, though, on 11th July 2025 - one day after it was full - the Moon rose at almost precisely the same azimuth that the ancient winter solstice Sun once did (exceeding it by ~9' of arc in declination, so rising fractionally south of perfection) and I was afforded the opportunity by Historic England and English Heritage to be on site to watch it happen.
I set up my camera to point along the sightline through the notch in Stone 58 and told it to take a photo every few seconds from 22:20 UTC+1 to catch the rising Moon.
Remarkably for England in the summer time the sky was clear to the horizon, and at 22:22:27 UTC+1 the first gleam of the Moon appeared.
Over the course of the next several minutes, the Moon gave me the chance to watch with my own eyes something very close to what the builders of Stonehenge would have seen at their winter solstice Sunrises.
Half orb occurred at 22:24:52 UTC+1.
Full orb followed at 22:27:01 UTC+1.
Overlaying several shots together, and with some calculation to produce the true position of the ancient winter solstice Sun, I'm able to show how close this Moonrise was to being spot on.
Ever since Prof. Gordon Freeman first suggested the existence of a secondary solstice axis I've been intrigued by his idea. Back in 2012, I helped confirm the calculations he made based on his 1990s observations near the winter solstice at Stonehenge because we had a perfectly clear sunrise that year but he and I could never actually observe it "truly" due to that pesky change in the Earth's tilt.
Thanks to the Moon's periodic excesses in rising and setting azimuths, I've now been able to see it with my own eyes.
It's hard to convey the sense of excitement I felt in the few minutes before first gleam appeared, and the enormous sense of satisfaction in watching the Moon behave exactly as anticipated.
There's something wondrous about peering through a narrow gap created by two stones erected 4,500 years ago and being perhaps the first person in several millennia to experience a ghostly echo of the spectacle the Stonehengineers intended.
The observations and technical details have been written up and accepted as a research article for the Journal of Skyscape Archaeology so if you fancy you can find that here: https://doi.org/10.1558/jsa.33686
