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A Black Moon is on the horizon

(WISH) – A rare lunar event that only happens about once every 18 months is happening Friday. It’s called a Black Moon.

The Black Moon is like a Blue Moon, which is a full moon that occurs twice within a month, but instead it’s the second “new” moon in a month.

The Blue and Black Moons do not refer to the actual color of the moon. Instead, it’s the overlapping that happens in the lunar cycle during a single calendar month.

From a new moon to new moon, which is referred to as a lunar cycle, takes about 29.5 days, while a single calendar month is generally 30 or 31 days. This causes the moon phases to move by about one day in each month.

Because of the shift, every once in awhile there will be a month with two full moons which is referred to as a Blue Moon. If there is two new moons in a month, which means the moon is invisible from Earth, this is referred to as a Back Moon.

The Black Moon will happen Friday, Sept. 30 at approximately 7:11 p.m. for those in the Western Hemisphere.

Unfortunately, you won’t be able to see it since the earth’s shadow will cover it.

The last time we had a Black Moon was in March 2014, and the next will be in July of 2019.CNN contributed to this report.