Once in a Blue Moon: Where the Phrase Actually Comes From
A Blue Moon happens when two full moons land in the same calendar month. It is not actually rare in astronomy terms. It happens every two to three years, but it is rare enough that the phrase "once in a blue moon" became shorthand for something that almost never happens.
This May 2026, we get two full moons. The Flower Moon in Scorpio peaked on May 1. The Blue Moon arrives on May 31 at 4:45 AM Eastern Time and it lands in Sagittarius at nine degrees.
This is unusual enough that it deserves its own ritual. Here is what to know and what to do with it.
Why Sagittarius matters
Sagittarius is the sign of the wish: the arrow for the shot at the future.
Where Scorpio digs underground and asks you what is buried, Sagittarius points up at the horizon and asks you what you are aiming for.
Sagittarius rules:
Long term goals
Travel and expansion
Belief, faith, and philosophy
Higher education and teaching
The future, three years out and beyond
A full moon in Sagittarius is the moment in the year when your wishes get a clear sky. It is the energy of an arrow being released, not drawn.
Why the Blue Moon adds power
The Blue Moon carries one specific magical reputation across multiple traditions. It is the moon you ask for the impossible thing on. The wish that is too big for a normal full moon. The thing you have been afraid to even say out loud.
Sagittarius is already the sign of the wish. A Blue Moon in Sagittarius is the wish moon amplified. It is a rare alignment and the kind of night you write down so you remember it.
The Blue Moon Sagittarius Wish Ritual
You can do this any time on May 31, but the energy is strongest from sunset May 30 through sunrise June 1. Outside is better than inside. Under the actual moon is better than not.
What you need:
A piece of paper
A blue pen if you have one. Any pen if you do not.
One candle, blue or white
A clear quartz point or any clear quartz crystal
A small dish of water left out under the moon
The steps:
Light the candle. Sit somewhere you can see the moon if possible.
On the paper, write one wish. One. The hardest part of this ritual is choosing. Sagittarius is honest, and Sagittarius does not reward hedging. Pick the thing you actually want, even if it scares you.
Underneath your wish, write three sentences answering the question: what would my life look like if this came true. Be specific. Not feelings, scenes. Where would you be standing. Who would be there. What would you be doing on a Tuesday morning.
Hold the quartz in your dominant hand and read what you wrote out loud. Quietly is fine. Whispering is fine. The moon hears whispers.
Fold the paper toward you three times, drawing the wish in.
Place the paper under the dish of water and leave both out overnight where moonlight can reach them.
In the morning, the water is now charged moon water. Use it however you would normally use moon water. Anointing candles. Blessing crystals. Watering a plant you love. Keep the paper somewhere you will see it for the next seven days, then burn it safely or bury it.
A note on Sagittarius full moons
Sagittarius is ruled by Jupiter, the planet of expansion. This means Sagittarius full moons amplify whatever you are already feeling about the future. If you are hopeful, you will feel hopeful in capital letters. If you are anxious about where your life is going, that anxiety will also be louder.
If the second category fits, the wish ritual is still the right move. Sagittarius does not reward sitting in fear. It rewards aiming.
The short version
The Blue Moon in Sagittarius on May 31 is the wish moon doubled. Pick one wish. Write it down with three sentences of what your life looks like if it comes true. Charge moon water under it. Aim the arrow.
Once in a blue moon is now.