A blue moon is an extra full moon: either the second full moon in one calendar month, or the third of four full moons in a single season. It is not actually blue. Spiritually, the blue moon meaning is about rarity, an unexpected second chance and the courage to finish or say something you have been putting off.
Blue Moon dates and times
Next blue moonSun, December 31, 2028 · 11:48 AMET
| Date | Time (ET) | Moon |
|---|---|---|
| Sun, May 31, 2026 | 4:45 AM | Flower MoonBlue moon |
| Sun, December 31, 2028 | 11:48 AM | Cold MoonBlue moonTotal lunar eclipse (blood moon) |
Times are US Eastern Time (ET), when the moon is exactly full or at the exact phase. It looks full for about a night either side.
You hear it in a song, in a toast, in a casual "that happens once in a blue moon," and sooner or later you wonder what the phrase is pointing at. The answer is a calendar quirk with a surprisingly tangled history, and the moon on that night looks the same pale gold or white as any other full moon.
What changes is the feeling. Because a blue moon arrives out of step with the usual rhythm of one full moon per month, many people treat it as a bonus night, a pause that was not on the schedule. This page explains the two definitions, how a 1946 magazine article scrambled them, the rare times a moon really has looked blue, and how people use the night for reflection. The dates table below shows when the next ones arrive.
What is a blue moon? The two definitions explained
The Moon takes about 29.5 days to go from one full moon to the next, a stretch astronomers call the synodic month. Our calendar months are mostly 30 or 31 days, so now and then a full moon lands on the 1st or 2nd of a month and the next one squeezes in before the month ends.
That gives the two accepted meanings of blue moon:
- Monthly blue moon. The second full moon within a single calendar month. This is the definition most people use today.
- Seasonal blue moon. The third full moon in a season that holds four, counted between an equinox and a solstice or the reverse. This is the older almanac rule.
A monthly blue moon can never happen in February, which is shorter than the lunar cycle, though it can happen in other months. Which month you see it in can also depend on your time zone, because a full moon at 11 p.m. in New York is already tomorrow in London.
Neither version says anything about color. It is simply a way of naming the full moon that does not fit the usual count of twelve a year.
How often does a blue moon happen?
Twelve lunar cycles add up to roughly 354 days, about eleven days short of a calendar year. Those spare days pile up, and every so often they add up to an extra full moon. On average that means a blue moon about once every two to three years, which is why the old saying fits so well: rare, but not impossible.
The spacing is uneven. Some stretches pass with two blue moons close together, others go several years with none. Seasonal blue moons follow a separate pattern, so the two types do not line up neatly.
A real blue moon is easy to prepare for. Because it is just a full moon, you do not need a telescope or a special viewing spot. Step outside after sunset, look for the rising Moon in the east and give it a few minutes as it climbs. The dates table on this page lists exact times, and it also helps to remember that a monthly blue moon is named by the calendar date where you live.
If you enjoy tracking cycles, a blue moon is a handy marker: a fixed point you can use to check in on goals set earlier in the year.
Blue moon history: the 1946 Sky & Telescope mix-up
For a long time, the blue moon was the seasonal one. Old almanacs used the term for a full moon that appeared out of sequence in a season, so that the seasonal names such as Harvest or Wolf stayed on the correct full moons.
Then, in 1946, the magazine Sky & Telescope published an article called "Once in a Blue Moon" by James Hugh Pruett. He read an older Maine Farmers' Almanac passage as describing the second full moon in a month, and printed that as the definition. The simpler rule caught on, partly because it was easier to check on an ordinary calendar. Decades later, researchers traced the mistake, and the magazine acknowledged the error.
By then the new meaning had spread so widely that it stuck. Today both definitions are considered legitimate, and many astronomy sites mention both.
The phrase "once in a blue moon" is older still. It appears in English writing from the 1500s, originally as a way to describe something absurd or impossible, the way you might say "when pigs fly." It gradually softened into "very rarely." It also turned into a staple of song titles, the best known written in the 1930s, usually standing for rare luck or lonely longing.
Has the Moon ever really turned blue?
Yes, though it has nothing to do with the calendar. A moon can look bluish when the air holds a great many tiny particles of a particular size, roughly a millionth of a meter across. Particles that size scatter red light and let more blue pass through, the reverse of what usually happens to sunsets.
The usual causes are:
- Volcanic eruptions. After Krakatoa erupted in 1883, observers around the world reported unusual colors in the sky, including moons described as blue or green. Later large eruptions, such as Mount St. Helens in 1980, were linked to similar reports.
- Large forest fires. Smoke from major wildfires has occasionally tinted the Moon and Sun blue or lavender.
These events are truly uncommon, and no two are exactly alike. That is a good reminder that "blue moon" as a calendar term and a blue-colored moon in the sky are two separate things that happened to share a name.
If you ever see a bluish moon after a volcanic eruption or heavy smoke, it is worth remembering that the air quality may be poor, so enjoy the view from indoors if the smoke is thick.
Blue moon meaning: spiritual significance
In most moon traditions, the full moon is a time of culmination: what you began at the new moon is visible and ready to be seen clearly. A blue moon adds one more full moon to that month, and the symbolism follows from that extra beat.
The blue moon meaning most often given is a second chance. Perhaps you missed the earlier full moon's invitation to finish something, forgive someone or make a decision. The blue moon offers another round, framed as an opportunity rather than a deadline.
A few other readings are common:
- Rarity and presence. Because it is uncommon, it nudges you to notice the ordinary rhythm you usually ignore.
- Doing the unusual thing. People link it with trying something outside routine: a conversation, an apology, a small risk.
- Perspective. The saying "once in a blue moon" becomes a question: what in your life happens rarely, and are you treating it as precious?
These are symbolic readings people choose to find meaningful, not predictions. The astronomy gives you a bonus full moon. What you do with it is up to you.
Blue moon rituals and ways to use the night
Since a blue moon is a second full moon in the same stretch, many people use it to review rather than begin. Here are practices that fit that spirit:
- Revisit the last full moon's intention. Look at what you wrote or promised, and note honestly what moved and what did not.
- Write a "once in a blue moon" list. Jot down things you rarely do but would like to: calling an old friend, visiting a place, finishing a project. Choose one.
- Release and forgive. Write a worry or a grudge on paper and tear it up or safely burn it, a common full moon practice for letting go.
- Charge your crystals. Some people leave stones on a windowsill overnight. This is a tradition, not something science supports, and it does no harm.
- Step outside. Even five quiet minutes looking up counts.
Keep the plan small. A blue moon works well as a prompt for one honest action rather than a long checklist. If something heavy comes up during your reflection, a trusted friend or a professional is a better support than any ritual.
Frequently asked questions
Is a blue moon actually blue?
Almost never. The calendar blue moon looks like any other full moon, usually white or pale gold. A truly bluish moon is rare and requires many fine particles in the air, as after a major volcanic eruption or large wildfires. The name refers to timing, not color.
Why do we say "once in a blue moon"?
The phrase predates the calendar meaning. In sixteenth-century English it described something absurd or impossible, since the Moon was not blue. Over time it softened into "very rarely." The extra-full-moon definition came later and fit the phrase well. The calendar sense simply fits it well.
Can there be a blue moon in February?
Not by the monthly definition, because February is shorter than the roughly 29.5-day lunar cycle, so it can hold at most one full moon in a normal year. February can still lose its full moon entirely in some years, which is a different curiosity.
Is a blue moon good luck?
There is no reliable evidence that it brings luck or misfortune. People often treat it as a bonus night for reflection, a chance to revisit an intention or try something unusual. Its meaning comes from the attention and effort you bring to it.
Do I need special equipment to see a blue moon?
No. A blue moon is a normal full moon, visible to the naked eye on a clear night. Look toward the eastern horizon shortly after sunset. Binoculars show craters and the dark lunar seas more clearly, but they are optional.
More moons
- Blood Moon · A total lunar eclipse and a copper-red Moon
- Supermoon · A full moon at its closest, bigger and brighter
- Full Moon Meaning · Completion, clarity and letting go
- New Moon Meaning · A dark sky and a blank page
- Crescent Moon Meaning · A thin curve of light and new growth
- Half Moon Meaning · Balance, decision and the turning point
- Gibbous Moon Meaning · Nearly full, almost there
- Wolf Moon · January's full moon of winter, instinct and belonging
- Snow Moon · February's full moon of stillness, scarcity and quiet hope
Angel number meanings are for reflection and inspiration. They are not predictions, and they are not medical, legal or financial advice.