What is a “Blue Moon,” and does the Moon actually look blue when it happens?

A Blue Moon can be one of several phenomena. In everyday usage, we talk about events that happen “once in a Blue Moon,” meaning once in a long while. Many call a second Full Moon during one calendar month a Blue Moon. The Moon does not appear blue during a Blue Moon.An older definition refers to a fourth Full Moon during a season — winter, spring, summer, or fall — instead of the usual three. Of the four Full Moons, however, the third is called the Blue Moon. This way, Full Moons that…