No single, universally accepted definition for the term black moon exists.
The assignment of a calendar date to a new moon, and in which month a second new moon occurs, depends on the time zone. For example, the new moon of 2016-10-01T00:11 UTC occurs on 1 October for Europe, Asia and Oceania, making it the first of two new moons in October. However, for the Americas the date is still 30 September, making this the second new moon of September.
- 2011-07-30
- 2014-01-30
- 2014-03-30
- 2016-10-30
- 2019-08-30
Season with four new moons
Another use of the term is for the third new moon in a season that has four new moons. This is analogous to the Farmers' Almanac definition of a blue moon as the third full moon in a season with four full moons. A season lasts about three months and usually has three new moons. This event occurs about every 33 months.