Stonehenge and the major standstill moon

A major lunar standstill happens only once every 18.6 years. Within a year or so either side of it, the moon can be seen from time to time rising or setting unusually far to the north or south. The longer sides of the Station Stone rectangle at Stonehenge, perpendicular to the main solstitial axis, align with the northernmost possible setting and southernmost possible rising positions of the moon. Researchers have debated for years whether this was deliberate—and, if so, how this was achieved and what might have been its purpose.

The next major lunar standstill takes place in January 2025, meaning that during this year and next there are rare opportunities to observe the moon rising or setting in line with the Station Stones. At various dates during this period I shall be working with my colleague Amanda Chadburn to observe this phenomenon at first hand so as to witness the 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.

Alongside another archaeoastronomer, Fabio Silva, and colleagues from Bournemouth University we shall be conducting our research on key dates this year and next.

Unlike the sun, tracking the moon’s extremes isn’t straightforward, requiring specific timing and weather conditions. The weather scotched our first attempts in March and early April but recent days have brought better fortune. And while our observations during English Heritage’s livestream on the evening of June 21 were unfortunately rained off, we were blessed with near-perfect conditions on the following evening (see picture; click on it to enlarge). EH will also be hosting a series of events during the autumn, including talks, a pop-up planetarium, stargazing and storytelling sessions, and a new display in the exhibition space. See here for more information on this.

More specifically, the aims of the project are to ground-truth the theoretical calculations of Stonehenge’s lunar sightlines, making allowance for the shift in the moon’s extreme position over the past 4500 years; to view the effects of the extreme moonrises and moonsets on Stonehenge itself (e.g. shadows, other visual effects); to view the impacts of modern features such as traffic and tree plantations during these astronomical events; to determine if any recommendations are needed with regard to World Heritage Site management; and to obtain a series of excellent photographs to record these rare astronomical phenomena in relation to the Station Stones and sightlines.

Top photo © André Pattenden/English Heritage. Middle and bottom photos © Amanda Chadburn.

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