A rare celestial event is set to occur tomorrow at Stonehenge, the most famous megalithic structure in the world. You can watch it on a livestream.
The English monument’s alignment with sunrise on the summer solstice - which takes place today - is well known. However, something else is happening, too: one of its southernmost moonrises during a rare lunistice or 'major lunar standstill.'
As well as the sun rising in the northeast behind Stonehenge’s Heel Stone on the summer solstice date, moonrise later that day will also be keenly watched for the effect of the 'major lunar standstill'. It occurs every 18.6 years, also known as a lunar cycle. This rare event occurs when Earth and the moon are at their maximum tilts, leading to the moon rising and setting at the extremes of its range. It sees the moon rise and set at its most extreme northerly and southerly positions on the horizon.
The moon will rise about five degrees beyond the ecliptic, the sun’s path through the sky. So the moon will rise, hang and set about five degrees lower in the sky than the sun does on the winter solstice.
“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.”
It’s believed that at least one major standstill was marked during the early phase of Stonehenge, potentially influencing the monument’s design and purpose, says English Heritage.
Scientists will be at Stonehenge throughout the “standstill season” to photograph the moments when the moon is in alignment with the Station Stones, reports Forbes. “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.”
English Heritage will be hosting a livestream on YouTube on 21 June from 21.30 BST (16:30 EST)