What Is A Blue Moon? When Is The Next Blue Moon?

"Once In A Blue Moon"

Over the years we have all at least heard, if not used the term, "once in a blue moon". Where does this come from and what does it represent?

Certainly it does not refer to the actual color of the Moon becoming blue. It is based on the occurrence of two full moons within any given month when you follow the "trendy" definition. This is the widely accepted definition as of this date in history. In the past, a blue moon was the third full moon of any season containing four full moons. This definition comes from various editions of The Farmer's Almanac.

So, keeping it simple, the blue moon is the second full moon that rises in the course of any given month.Lunar cycles are 29.5 days therefore somewhat less than an actual month. With this being said, there will never be a blue moon within the month of February as there simply is not enough days in February to host two full moons.

On average blue moons occur approximately every 33 months or close to every three years. It is from the period time between these blue moons that came the saying, "once in a blue moon", to signify that it does not or will not happen very often. There are exceptions to this time between full moons. An example is January and March of 2018. There will be blue moons within both of those months.

According to what I call the "trendy" definition of the blue moon we experienced a blue Moon in August of 2012. The first full moon was on August 2, 2012, and the next full moon, the blue moon, was on August 31, 2012.

Following the August 2012 blue moon, the next blue moons will occur in July of 2015, January & March of 2018, and October of 2020. (To view all future Blue Moons, click the link below to view the Blue Moon Calendar.)

Following the definition of the Farmer's Almanac, with the third full moon within a quarter, the next blue moon was on August 21, 2013.

Which ever definition you find yourself following, as you can see, the blue moon is a rather rare occurrence. Keeping that in mind, when you use the phrase, "once in a blue moon", you are accurately describing what you consider to be a rather rare event within a period of time.

Note: There are atmospheric conditions that can occur at times that will actually make the moon appear to be blue in color. Haze and smoke in the atmosphere can certainly alter the color of the moon as well as other astral bodies that are floating around out there.

One must keep in mind, however, that these atmospheric conditions are not what is referenced when thinking about the term, "once in a blue moon".

Blue Moon Calendar