Many people have heard of the harvest moon or talk about things happening “once in a blue moon,” but few know where these names come from. The majority of pre-Christian calendars were lunar-based, following the cycles of the moon as a way of keeping time. The changing of the moon was regular and easily recognizable, and thus became a basis for some of the earliest methods of time-keeping and tracking the seasons in cultures world-wide. These cultures also created many stories and myths about the moon and why it changed. Here is some of the mythology relating to lunar cycles.

Based on it’s orbit around the Earth in relation to the Sun, the Moon sometimes appears full and round in the sky, sometimes as a thin sliver. These changes are purely visual, depending on how much of the Sun’s light is blocked by the Earth. The terms “waxing” and “waning” are used often with the Moon. Waxing is the phase where a larger and larger area of the Moon is illuminated, waning is when this area is reduced. The term “gibbous” is also used, meaning “more than half but less than fully illuminated” as a way of describing what is seen.

As it rotates around the Earth, the Moon goes through various phases which repeat endlessly: Full Moon, Waning Gibbous Moon, Last Quarter Moon, Waning Crescent Moon, New Moon, Waxing Crescent Moon, First Quarter Moon, Waxing Gibbous Moon and back to Full Moon again. In times before artificial light, the Full Moons were very important as they shed bright light later at night allowing for more work.

The tradition of naming the Full Moons in Northa America came from Native American tribes, using them to mark certain times of hunting, planting or harvesting, especially tribes of the Northeastern parts of the United States. European settlers adopted some of these customs and added some of their own traditions. As each lunar orbit is really about 29 days, the full moons shift in their positions within the months a bit from year to year, which is why some months have variable names.

When it comes to "blue moons," there are a variety of definitions. Some sources say it is any second full moon in a month. However, there are those who claim that is inaccurate, and that blue moons are really when a fourth full moon occurs within a season (3 month timeframe). This would mean that some 2nd full moons within a month could be called "blue" but only if they were the fourth one in that season, and sometimes the blue label would fall on a single full moon.