There are events that happen once in a blue moon—but events that happen once in a black moon occur just as often.
This weekend, the world will experience a black moon. The moon itself won’t actually turn black.
The term “black moon” refers to either two new moons in the same month or four new moons in a single season.
The summer of 2025 will have four new moons, and the third of them this season receives the black moon designation.
Black moons are rare occurrences. A new moon happens about every 29.5 days. Since most months are 30 or 31 days long, and a season is roughly 91 days, a black moon usually requires a new moon to fall on the first day of a month or season.
A blue moon happens just as often—when there are two full moons in a month or four in a single season.
One thing that makes a black moon more exciting for astronomers than a blue moon is that the new moon phase offers darker skies for viewing stars and planets. In contrast, the bright light of a full moon tends to wash out other objects in the night sky, making them harder to see.
The next full moon will occur on Sept. 7 and will coincide with a lunar eclipse. Unfortunately for Americans, this eclipse will happen during the daytime, meaning only viewers in Asia, Europe, and Africa will be able to see it.
This new moon will also bring a partial solar eclipse, but that event will only be visible in parts of the Southern Hemisphere.
