What Is a Black Moon? The Unusual Sky Phenomenon Will Occur Later This Month, but Don’t Expect to See It
A seasonal black moon, to appear on August 22 or 23, is the third of four new moons within an astronomical season
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This month, the lunar cycle will treat us to a relatively rare astronomical treat: a seasonal black moon. There’s just one problem—the phenomenon is essentially invisible. Fortunately, however, it still offers a good reason to raise your eyes to the sky.
A “black moon” isn’t an official astronomical term, according to the Weather Network’s Scott Sutherland. It can refer to two different, but related, events: either the third of four new moons within the same astronomical season or the second of two new moons within the same calendar month. Astronomical seasons are based on the solstices and equinoxes, whereas meteorological seasons depend on the yearly temperature cycle.
For most of the planet, the black moon will occur on August 23, though for some places far behind Coordinated Universal Time (UTC), it will take place on August 22, as reported by Time and Date’s Eloise Elliott.
In case you need a refresher, new moons are the opposite of full moons, and they occur about every 29.5 days, as part of the lunar cycle. During the new moon, the sunlit side of the celestial body faces away from Earth, hiding the moon in our daytime sky. A solar eclipse can only happen during a new moon.
Fun fact: Phases of the moon
The sun always illuminates half the moon’s surface—we just see different phases of the moon based on how much of the bright face is turned toward Earth.
Black moons are notable, because usually, there are only three new moons per astronomical season and just one per month. This August’s event, a seasonal black moon, only occurs once every 33 months or so, per Time and Date. Full moons follow a similar pattern in that there are also usually only three per season and one per month. The full moon’s equivalent of a black moon—the third of four full moons within the same season or the second of two full moons in the same month—is called a blue moon.
National Geographic’s Michael Greshko wrote in 2016 that a black moon “is like the evil twin of a blue moon,” while noting that astronomical events don’t actually foreshadow bad news or the end of days, despite some dubious internet reports claiming otherwise at the time.
Since black moons are a special kind of new moon—and you can only witness a new moon when it eclipses the sun—don’t expect to get a good look at Earth’s natural satellite this time around. If the weather is clear, however, a new moon makes for a dark sky and a great stargazing experience.
The term “black moon” has one more definition—and this is the rarest of them all. Because February is only 28 days (or 29 during a leap year), it’s shorter than the 29.5-day lunar cycle. This means that every once in a while, February will have either no new moon or no full moon that falls during the month. When this happens, it’s also known as a black moon, and these events are often 19 years apart, per Time and Date.
Perhaps in addition to saying “once in a blue moon,” we can also start using “once in a black moon.”
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