A second full moon in a single calendar month is sometimes called a "Blue Moon." By this definition, a Black Moon is the flip side of a Blue Moon: the second new moon in a single calendar month.
The second new moon of December will occur tonight, at 5:27 p.m. ET (2227 GMT) on Dec. 30, according to the U.S. Naval Observatory, two days after the waning moon passes by Mercury in the predawn sky.
In reality, the moon isn't generating light; it's reflecting sunlight. There are eight phases of the moon during a 29.5-day cycle: new moon, waxing crescent ... of a blue moon is the second ...