The black moon is set to occur at 5:37 p.m. ET on Monday, according to the U.S. Naval Observatory. What Is a Black Moon? New moons occur every four weeks. A monthly black moon, which is not an ...

Something rare is happening in the skies in the next few days — a black moon. This rare celestial event is due to an unusual calendar alignment: two new moons in one month. The first occurred on Dec.