Volcanic ash or smoke particles that are approximately 1 micron (one millionth of a meter) in diameter. These particles scatter red light while allowing blue light to pass through, creating a blue hue.
Contrary to popular belief, a Blue Moon is not defined by its color. There are two distinct definitions for this event.
In short, a Blue Moon is mostly a calendrical quirk, not a color change—but on rare occasions, the sky truly delivers a blue lunar glow.
