Just as the term “Blue Moon” applies to instances of 2 full moons in a month or 4 full moons over a 3 month period, there is a similar term that applies specifically for new moons happening in the same time period. This occurrence of new moons is called a “Black Moon,” which isn’t strictly an official astronomical term, nor is there a universally accepted definition.
Of the 4 definitions, 2 relate to the month of February and 2 relate to the number of new moons over a period of months. The two definitions that relate to February are related to either the lack of a full moon or new moon during the month. When there isn’t a full moon from a calendar month of February, either the prior December or January or the following March or April will have 2 full moons. In the event that February lacks a new moon, the same will be the case as with no new moon, 2 new moons will be in in December, January, February, or March. The occurrence of either no full moon or no new moon in February occurs every 19 years.
For the definition that sees the term used to define the occurrence of a second new moon in a calendar month, makes the event analogous to the by-month definition of a blue moon as the second full moon in a month. By this definition, a Black Moon will occurs roughly every 29 months.
The last use of the term is for the third new moon in a season that has four new moons, which again similar to how some define 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, which makes this occur about roughly 33 months. When this happens, there is no dependency on time zones in this definition as the seasons are tied to the winter solstice.
On average, a Black Moon does occur every 32 months, with certain occurrences only in certain time zones. This makes the event a somewhat unusual celestial event. The next Black Moon won’t arrive until January 31st, 2022, and the 2nd Black Moon will be March 31st, 2022. The next Black Moon by the seasonal definition of the term will occur on May 19, 2023.
The next time the Pacific Northwest will have 2 Black Moons in 1 calendar year will be in 2033.