The term blue moon has several meanings:

Most correctly, a blue moon refers to a full moon that is blue in color. Under clear skies, this occurs when the planet Venus is close to Earth. Venus illuminates the full moon making it appear slightly pale blue in color. This gave raise to the old expression, "once in a blue moon", meaning "not often."

In magic, a blue moon is very significant as it is considered an unusually good time to set specific goals in one's life.

The blue moon has always been recognized as a special event and an especially romantic time. So, next time you see a blue moon think about your personal goals and that special someone in your life.

In astrology, a blue moon refers to the second full moon while the sun has remained in the same sign of the Zodiac.

Especially in the United States, a blue moon has incorrectly come to mean a second full moon within a calendar month.