BellaOnline Forums Education Astronomy Once in a Blue Moon

Once in a blue moon is a common English expression and it refers to a rare event. But why a blue Moon? And what is a blue Moon if it isn't blue? There is no unique answer, but here are a few things it could be.

Once in a Blue Moon

The recent "blue moon" of August 20/21 2013 was the third of four full moons of the summer season. There will be a fourth one before the equinox. In England this is the Fruit Moon. What about where you live?

Found a nice infographic showing the calendrical meanings of blue Moon.

It is a very rare happening for the Moon actually to look blue. I've never seen it, though I've seen the Moon look pink, orange, rusty and red. In this picture of a blue Moon over Texas, it was probably due to tiny water droplets in the atmosphere.

There's a lot of fuss about a month with with two full moons, but what about poor February? The lunar cycle is about 29 and a half days, so every now and again, February doesn't have a full moon at all. This happened in 1999. It happens again in 2018. So this *no* moon is much rarer than either of the calendrical *blue* moons!

Astronomers can be so romantic. A Canadian astronomer used the August blue moon to propose to his girlfriend in an unusual way. He miniaturized the words "Will you marry me?" to fit in a telescope eyepiece. When she looked through the telescope, the proposal appeared to be written on the full Moon. (I'm glad it didn't rain.)

Here is the story of the proposal with pictures.

This year 2018 has two "blue" moons in a row. January had one and tomorrow's full moon will make the second full moon in March. And of course this means that February had no full moon.

I'd better look.

still miss the notifications.


It's a bit overcast tonight but the moon is big and bright.

Here's a picture taken by Eric Houck of the January 2018 'blue moon". Note that this is a tribute to the ingenuity of the photographer, not anything special about this full moon. To get the moon lined up with the tree, he'd have to find the right place to get the shot. The Moon also looks BIG because it's low in the sky and the photographer is a long way from the foreground scene. (People do that to make a "supermoon" look extra big.)

This explanation of a blue moon made me laugh.