This year will see (kind of) another rare astronomical event taking place across the night sky. On December 30-31, we will have a rare Black Moon to see out 2024.

What is a Black Moon?

You’ve probably heard of a Blue Moon; it’s a far more well known phenomenon that is different from a Black Moon but is useful for understanding them nevertheless.

A Blue Moon, which earnt its name from the 1937 edition of the Maine Farmer’s Almanac, can occur in two situations. It is either the third full Moon in a season with four full Moons (seasons typically only have a three full Moons), or the second full Moon in a month.

Interestingly, this second definition is the most popular one, but it is actually built on a misunderstanding. In a 1946 piece written for Sky and Telescope magazine, James Hugh Pruett incorrectly referred to the Blue Moon as the second moon in the same month. Although he got this wrong, the idea has stuck around ever since.

This explanation is confusing but important because Black Moons also have two definitions that operate along similar lines. But if a Blue Moon is based on the number of full Moons in a given period, a Black Moon is based on the number of new moons. So, it is either the third new Moon in a season with four new Moons (just like its Blue counterpart) or it is the second new Moon in a single month.

The coming Black Moon will be an example of the second definition and will occur at 4:26 pm CST (10:26 pm UTC) on December 30, 2024. This means it will be December 30 for America, but December 31 for Europe, Africa, and Asia.

Black Moons are rare, but the one that is defined as the second of two in a single month are more common (occurring once every 29 months) than the seasonal definition (occurring every 33 months). The last one occurred on May 19, 2023.  

Unfortunately, as rare as this type of astronomical event may be, it is not actually visible in our sky. As with any new Moon, a Black Moon occurs when the Moon is pretty much between the Earth and the Sun, making it difficult to see because the side that is illuminated by the Sun is facing away from the Earth. However, the absence of the Moon in the night sky can also make it a great time to do more general star gazing, as there is less light to get in the way.

And if you’re waiting for the next Blue Moon, the next time two full Moons appear in the same month is May 31, 2026, and the next seasonal Blue Moon is May 20, 2027.