Blue Moon 2015: When To See The First Since 2012

By Marc Torrence (Patch National Staff)

Once in a blue moon? That’ll be Friday, the first in nearly three years.

A blue moon occurs when there are two full moons in the same month. Because a moon cycle lasts for about a month, the timing has to be just right to get two in the same month.

July 2 was a full moon. July 31 will be, too. Hence, blue moon 2015.

The last time this happened was August 2012, when there was a full moon on August 31 that year.

To answer a common question: no, the moon won’t actually be the color blue.

While there are some conditions that can cause the moon to appear a shade of blue—smoke, a concentration of certain particles—the name has nothing to do with the moon’s color.

It dates back to a 16th-century piece of literature using the word “belewe,” to betray, to refer to a moon that doesn’t properly mark the end of a farming season.

The “blue” caught on in the early 1900s and originally referred to the third full moon in a season with four.

Now, the most common definition refers to two full moons in the same month.