Each month we have a full moon and a new moon, but sometimes we have an exception to the rule. That exception this month is called the Black Moon. 

When a month has two full moons, the second moon is called a Blue Moon, an event which occurs every two to three years. When a month has two new moons, the second is called a Black Moon. Here's where it gets tricky. The moon can also be called a Black Moon in a month with no new moon, no full moon.

On September 30, 2016, we will have a second new moon in the calendar month. This only occurs once every couple of years. The last Black Moon was in March of 2014.

Too bad we can't see the  Black Moon. A full moon refers to the moment when the moon's Earth-facing side is fully illuminated by sunlight, Space.com say's a new moon refers to the moment when the moon's Earth-facing side is fully in shadow. (Unfortunately, that means the Black Moon will be more or less invisible, even if the moon is high in the sky).


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