A farmer in Maine once kept a calendar where a season’s fourth full moon was called “blue.” A century later, that name meant something else entirely. The sky does not change. Our naming of it does. A Blue Moon is the second full moon in a calendar month or the third of four full moons in a season. A Black Moon is the second new moon in a month, the absence of a full moon in a month, or the third new moon in a season. Both are rare, but their meanings diverge sharply between astronomy and occult practice.
What exactly are a Blue Moon and a Black Moon?
The definitions are not one. They are two, and sometimes three.
A Blue Moon has two competing definitions. The older one comes from the Maine Farmers’ Almanac: the third full moon in a season that contains four full moons instead of the usual three. The newer one, now common, is the second full moon in a single calendar month. Both describe a full moon that appears more often than the standard one-per-month.
A Black Moon has three definitions, none of them official in astronomy. The most common in occult circles is the second new moon in a calendar month. Another is the absence of a full moon in a month (which can only happen in February). A third is the third new moon in a season of four new moons. In all cases, the Black Moon is a new moon, not a full one.
The two events are opposites in the lunar cycle. One is a surplus of full moons. The other is a surplus of new moons.
Where do the names come from? A history of confusion
The term “Blue Moon” is older than most people think. It appears in a 1528 pamphlet by William Roy and Jerome Barlow, where “blue moon” meant something absurd or impossible, like “the moon is made of green cheese.” By the 19th century, the Maine Farmers’ Almanac used “Blue Moon” to label the extra full moon in a season. That almanac followed a system where each season had three full moons, named for the months. When a fourth appeared, the third was called “Blue Moon” so the fourth could keep the seasonal name.
The modern monthly definition came from a 1946 article in Sky & Telescope by James Hugh Pruett. He misinterpreted the almanac’s rule and wrote that a Blue Moon was the second full moon in a month. The error stuck. In 1999, a popular radio show used the monthly definition, and it became the standard for most English speakers.
The Black Moon has no such paper trail. The term appears in 20th century astrological and occult texts, often as a counterpart to the Blue Moon. It gained traction in online pagan communities in the early 2000s. No single source claims authorship. It emerged from the same naming impulse that gave us “Supermoon” and “Blood Moon.”
What do they mean in occult practice?
The meanings follow the phase. A Blue Moon is a full moon, and a full moon is a time of culmination, visibility, and power. A Black Moon is a new moon, a time of concealment, beginnings, and shadow.
In many traditions, the Blue Moon is treated as a “power-up” full moon. The energy that peaks during any full moon is said to be stronger because the moon is already at its maximum and then appears again in the same cycle. Practitioners use it for work that needs extra force: long-term intentions, group rituals, charging tools that will be used for a year. Some covens hold a Blue Moon sabbat, treating it as an additional festival outside the usual eight.
The Black Moon carries the opposite charge. It is the dark moon, invisible, the time when Hecate walks. In Greek folk magic, the new moon was sacred to Hecate, and offerings were left at crossroads on the night of the dark moon. Modern practitioners often reserve the Black Moon for solitary work: scrying, shadow work, banishing, and divination that looks into hidden things. The absence of light is not emptiness. It is potential.
A concrete practice: on a Black Moon, some light no candles. They sit in the dark and listen. The fire is not decoration. It is the altar.
How do the two compare to other lunar events?
The Blue Moon and Black Moon are not the only named lunar events. A Supermoon occurs when a full or new moon coincides with the moon’s closest approach to Earth (perigee). A Blood Moon is a total lunar eclipse, when the moon appears red from Earth’s shadow. A Harvest Moon is the full moon closest to the autumnal equinox.
The key difference is that Supermoons, Blood Moons, and Harvest Moons are observable phenomena. You can see the size, the color, the timing. Blue Moons and Black Moons are calendar constructs. The moon itself looks no different. The rarity is in the naming, not in the sky.
That makes them more interesting for occult work. The meaning is assigned, not observed. A practitioner chooses to treat a Blue Moon as powerful because the calendar says it is rare. The moon does not know it is blue.
Common misconceptions about Blue Moons and Black Moons
“A Blue Moon is actually blue.” It is not. The name comes from the calendar, not the color. On very rare occasions, volcanic ash or smoke can make the moon appear blue, but that has nothing to do with the term.
“A Black Moon is a lunar eclipse.” No. A lunar eclipse is a Blood Moon. A Black Moon is a new moon, invisible to the naked eye.
“They happen every 2.7 years.” That is roughly true for the monthly Blue Moon. The seasonal Blue Moon occurs about every 2.5 years. Black Moons are less regular because they depend on the month length. A February without a full moon happens about every 19 years.
“You can see a Black Moon.” You cannot. A new moon is not visible. The Black Moon is defined by its absence.
FAQ
How often does a Blue Moon occur?
A monthly Blue Moon happens about every 2.5 to 3 years. A seasonal Blue Moon happens slightly more often, about every 2.5 years.
What does a Black Moon mean in witchcraft?
It is a time for shadow work, banishing, and divination. Many practitioners treat it as Hecate’s night and work alone.
Is a Black Moon the same as a new moon?
It is a new moon, but not every new moon is a Black Moon. A Black Moon is the second new moon in a month or the third in a season.
Can a Blue Moon and a Black Moon occur in the same month?
Theoretically yes, if a month contains two full moons and two new moons. That requires a 31-day month and precise alignment. It is extremely rare.
The Blue Moon and Black Moon are reminders that we name the sky to make sense of it. The moon does not care what we call it. But the act of naming gives us a handle on time, a reason to pause, a moment to work. If you want to track these events for your practice, start with a lunar calendar and mark the second full or new moon. That is where the work begins.
For more on lunar cycles and their uses, see our guide to moon phases in magic. The glossary entry on lunar terms covers Supermoons, Blood Moons, and Harvest Moons. And our astrology hub connects moon phases to planetary hours and timing.