In astronomy, the term black moon is neither well-known nor frequently used. As a consequence it has no accepted definition, but seems to have occasionally been applied to at least four different situations:
| Definition | Notes |
|---|---|
| 1. The second occurrence of a new moon in a calendar month.[1] | Cannot occur in February. Analogous to the common calendrical definition of a blue moon for months with two full moons. |
| 2. The third new moon in a season that has four of them. | Analogous to the Farmers' Almanac definition of a blue moon for seasons with four full moons. |
| 3. The absence of a full moon in a calendar month. | Can only occur in February, thus January and March will each have a second full moon (a calendrical blue moon). |
| 4. The absence of a new moon in a calendar month. | Can only occur in February, thus January and March will each have a second new moon (see definition 1). |
In myth and folklore the full moon of each month is given a name. In many cases the waxing moon and waning moon are also given names. There are many variations, but the following list gives the most widely known names:
The third full moon in a season with four full moons is called a blue moon, as described in the Maine Farmers' Almanac. Until recently it was commonly misunderstood that the second full moon in a month was the blue moon. However, it was recently discovered by Sky & Telescope magazine and reported on NPR that the interpretation of a blue moon as the second full moon of the month was erroneously reported in a 1946 issue of Sky & Telescope and then perpetuated by other media.
In some cultures, individuals whose birthdays fall on or near a harvest moon must provide a feast for the rest of the community.