Are you ready for a rare lunar phenomenon that won't happen again for almost 19 years? This weekend will see the rise of the "Cold Moon," the name for December's full moon. However, the moon will behave dramatically differently from usual, with the most northerly moonrise and moonset at full moon until December 2043, according to Timeanddate.com.
Here's everything you need to know about seeing the Major Lunar Standstill this weekend -- and why it will be celebrated at Stonehenge and other ancient sites:
According to English Heritage, the major lunar standstill is when the northernmost and southernmost moonrise and moonset are furthest apart.
The moon has an 18.6-year cycle during which the exact places it rises and sets on the horizon waxes and wanes. At each end of that cycle is a major lunar standstill, also called a lunistice, a rare celestial event that occurs when Earth and the moon are at their maximum tilts. That leads to the moon rising and setting at the extremes of its range. These extreme rise and set positions occur during a two-year period.
Earth rotates on an axis tilted by 23.4 degrees, so the sun rises and sets within a range of about 47 degrees throughout the year. The sun's path through the sky is called the ecliptic.
Since the moon's orbit is tilted by 5.1 degrees relative to the ecliptic, it rises and sets within a 57-degree range in any given month.
The full Cold Moon will rise and set at its most extreme northerly points on the horizon on Sunday, Dec. 15, 2024.
It follows the southernmost moonrise of this major lunar standstill, which occurred with the rising of the full Strawberry Moon on Friday, Jun. 21, 2024.
During a major lunar standstill, the moon rises and sets at its most extreme northerly and southerly positions on the east and west horizons, respectively. It will see its most northerly rise and set this weekend, so get somewhere high up with a clear view of the horizon. If there's somewhere you regularly watch the full moon rising from, go there -- the extreme northerly rising point, where it first appears at the time of moonrise where you are, will astound you.
As a bonus, December's full Cold Moon is also the highest-hanging in the sky, so it will pass at the highest possible path through the sky. That's because the moon mirrors the sun's path across the sky. Since the sun is at its lowest in the sky this month, as seen from the northern hemisphere, the full moon -- opposite the sun -- must be the highest. As a result, it will also be in the night sky for longer than any other full moon of the year.
Some stones at Stonehenge may have been set to mark the major lunar standstill, according to The Guardian, but it's not the only ancient monument that is thought to double as a sophisticated astronomical observatory. It's thought that the 3,000 megaliths of the Carnac Stones in Brittany, France, mark the extreme positions of the moon during a major lunar standstill. The Callanish Stones on the Isle of Lewis in the Outer Hebrides, Scotland, also align with the southerly rising and setting points during a major lunar standstill.
The next most northerly moonrise and moonset after this weekend will occur in December 2043.