This Friday, something rare is about to happen that you'll find yourself uttering, "One in a blue moon." And indeed, a phenomenon that's literally about a blue moon is going to happen. 

The Christian Science Monitor has learned the reason why the blue moon is considered very rare. Apparently, the Earth typically has 12 full moons in a year, one for each month. When the Earth experiences 13 full moons however, the extra full moon display is considered the blue moon.

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So how does this happen? Experts say the full moon to full moon cycle averages 29.53 days except of course for February. The extra days that are not counted in the cycle, technically called synodic month, accumulate over the years and this is when 13 full moons are recorded in some occasions. 

Nevertheless, since there isn't an extra month, blue moon refers to the second full moon in a month, as per Irish Examiner.

The last time the Earth experienced a blue moon was three years ago, specifically on Aug. 31, 2012. According to the calculations of experts, the next blue moon is bound to happen three years from now, so it's going to happen on Jan. 31, 2018.

The greatest misconception about the blue moon phenomenon though is the color of the celestial body. Instead of seeing a literally blue moon, the one that will appear in the night sky is a silvery grey moon. 

While this may not be a spectacular view, you should be thankful that you are not seeing a blue moon from where you are standing. Based on expert observation the only time you will see a literally blue moon is when you are near a volcano that's spitting ash at nighttime. This is very evident in 1883 when the Indonesian volcano Krakatoa erupted and spewed ash into the atmosphere that gave the atmosphere a bluish tinge event at night. 

Interestingly, the most recent time when a real blue moon graced the sky was back in Sept. 1950, when ash and smoke from an Alberta, Canada forest fire formed into a patch of clouds that seemingly gave the moon a distinct blue hue when viewed from the Royal Observatory, according to CNN. 

TagsBlue Moon, moon