Astronomy and outer space have always fascinated me. 'On Friday, May 19, the year's only "black moon" will rise in the sky — and there will be precisely nothing to see'. An event like this only takes place around every 33 months. The term "black moon" does have other meanings, and is a term that describes other lunar events. But in this case, it refers to the third new moon in an astronomical season with four new moons.
The definition that best fits this month's event is a "seasonal black moon" — the third new moon in a season with four new moons. That's something that only happens every 33 months or so...