A hidden 'Black Moon' rises this week. Here's what that is
We see a lot of Full Moons, but what's a 'Black Moon' all about?
Attention, skywatchers and astronomy enthusiasts! A fascinating and rare celestial event will take place on the 22nd or 23rd of August, depending on your timezone.
While many are familiar with the term "Blue Moon," the Black Moon represents a unique occurrence in the lunar calendar, characterized by the absence of visible light from the Moon during specific periods.
What is a Black Moon?
You've likely heard of a Blue Moon, in at least one of its two incarnations:
the third of four Full Moons that occur within the same astronomical season, or
the second of two Full Moons that occur within the same calendar month.
The reason these events are remarkable is that we usually only see three Full Moons in a season, and one Full Moon per month.
Every 2-3 years, though, the timing works out that there's a Full Moon that occurs within a few days after the start of a season. In that case, with the Moon's 29.5 day cycle, the following three Full Moons will also happen within that same season. Similarly, if a Full Moon occurs on the 1st or 2nd of a month, depending on what month that is, we can also see another Full Moon at the end of that month. (This can never happen in February, even on a leap year.)
During each lunar cycle, though, for every Full Moon, there is a corresponding New Moon that occurs. These are up during the day, essentially hidden from us by the glare of the Sun. However, tracking their frequency, we also typically have one per month and three every season.
Due to their exact timing, though, patterns emerge similar to the occurrence of Blue Moons, which are called Black Moons:
the third of four New Moons that occur within the same astronomical season, or
the second of two New Moons that occur within the same calendar month.
The three Full Moons and four New Moons of summer 2025, with the August Black Moon occurring on the 22nd or 23rd of August (depending on your timezone). (Scott Sutherland/NASA's Scientific Visualization Studio)
During the astronomical summer of 2025 (June 19/20 to September 22) there are four New Moons, which occur on June 25, July 24, August 23, and September 21. The third of those, coming up later this week, is therefore a seasonal Black Moon. The last seasonal Black Moon was in May of 2023, while the next will occur in August of 2028. The last calendar Black Moon was on either November 30 or December 30 of 2024 (depending on which time zone you live in), with the next one due on August 31, 2027.
Given that it isn't an official term used in astronomy, the name Black Moon has been used to describe a few other events, as well. Specifically, it is often used to refer to a February without a Full Moon (and this is only possible during the month of February). The last time this happened was in 2018, and the next time will be in 2037. Similarly, some have called it a Black Moon when there is no New Moon in February, which last occurred in 2014, and will happen again in 2033.
Although we won't be able to see this year's seasonal Black Moon, it does mark the night of August 22-23 as an excellent time to get out for some skywatching. In fact, without any moonlight in the sky, that could be the best night of the month to gaze up at the stars.
This article includes contributions from Scott Sutherland, Senior Science Writer for The Weather Network. Thumbnail image depicts the August 2025 Full Sturgeon Moon (left of centre), courtesy NASA's Lunar Reconnaissance Orbiter and NASA's Scientific Visualization Studio, while in the background are the four New Moons of summer 2025, also courtesy LRO and SVS, with the August 22/23 Black Moon highlighted for emphasis.