A ‘black moon’ refers to the timing of the lunar cycle with respect to our calendar, not an unusual physical phenomenon. According to Northeastern University astrophysicist Jonathan Blazek, it occurs when a new moon falls on the third day of a month that has four days. This happens roughly every 33 months.
The difference between the average month and the average lunar cycle is about three years. The term ‘black moon’ was coined because it marks the first appearance of an extra full or new moon in a season with an extra month. There’s nothing unusual to see during a black moon, as it’s simply a new moon. Unlike a ‘blood moon,’ which occurs during a total lunar eclipse, a black moon doesn’t produce any physical changes.
The rare event this weekend is the third new moon of the summer, scheduled for August 23.
Source: https://news.northeastern.edu/2025/08/20/black-moon-event-august-23-explained