The phenomenon occurs about once every 32 months, when there is a second new moon in a month
An unusual type of supermoon is set to take the stage Wednesday night. It's called a "black supermoon," and what makes it unlike other so-called supermoons is that it's basically invisible.
The black moon comes when the moon is near its closest point to our planet along its orbit of Earth. This is called perigee syzygy or simply... a supermoon.
A new moon refers to the moment when the moon's Earth-facing side is fully in shadow, which unfortunately means the “Black Moon” will be more or less invisible.