You probably haven’t heard of the term “black moon” before.  In astronomy or popular culture, the term black moon is not well-known or much used, but it’s an interesting oddity.

I could not find a definitive definition. In fact, I found four different definitions.

First, is when there is the second occurrence of a new moon in a calendar month. That happened 30 August 2008,  and will occur again on  30 July 2011.  Not to be confused with the analogous and more common definition of a blue moon for months with two full moons.

The third new moon in a season that has four of them is sometimes called a black moon.  It happened on 23 August 2006, and will occur again 20 May 2012.

My personal preference for defining a black moon is when there is the absence of a full or new moon moon in a calendar month. That happened in February 1999 when there was no full moon, and it will happen in February 2018. This can only occur in February.  (January and March each have a second full moon.)

There can also be the absence of a new moon in a calendar month, as was true in February 1995 and (mark your calendar) again in February 2014.