John explains: Just what is a Blue Moon?

John explains: Just what is a Blue Moon?

LUBBOCK, TX (KCBD) - An event that will not occur again until 2018 took place on Friday.

It was a 'blue moon', or second full moon in one month. The first full moon was July 2.  By definition, a blue moon occurs about every three years.

During most years, the Earth experiences 12 full moons, one per month. However, in some years, such as 2015, according to, this year has 13 moons and the extra lunar display is known as the blue moon.

The term blue moon became the unofficial definition thanks to Sky and Telescope magazine in 1946. An article refered to a blue moon as the second full moon in a calendar month and that created the most widely accepted definition used these days.

While a full moon appears to last all night, it is technically an instantaneous event, occurring when the sun, Earth and moon fall close to a straight line. The event happens at the same instant across the globe, this time exactly at 6:43 am EDT Saturday.

One last note, the word blue is thought to be called after an old English term meaning 'betrayer' since it occurs because of a quirk of the calendar.

Photo courtesy of Eduardo Munoz; Rueters News.

Copyright 2015 KCBD. All rights reserved.