What is a Paschal Full Moon?

by Jaime McLeod | Monday, April 11th, 2011 | From: Astronomy

The full Moon has many names — so many that it can be hard to keep track of them all. There are monthly full Moon names from English, Algonquin, and many other traditions. These include Strawberry Moon, Hunter’s Moon, Snow Moon, Pink Moon, Beaver Moon, and the like, and are listed in the Farmers’ Almanac.

Because the names come from different sources and cultures, each month’s full Moon may have half a dozen or more names. Last year, Farmers’ Almanac readers even added their own favorite modern names to the names from antiquity.

Then there are the names with somewhat complicated rules, such as a Blue Moon or the Harvest Moon. The definition of a Blue Moon has changed over time, but today we use it to describe a second full Moon during a calendar month. Most people think the Harvest Moon falls in September, and in many years, that’s true. Unlike the set monthly full Moon names, though, it can change from year to year. A Harvest Moon is technically the first full moon after the autumnal equinox. Some years, it coincides with September’s full Moon, the Corn Moon, and other years it falls during October’s Hunter’s Moon.

Add to this list the Paschal Full Moon. Simply speaking, the Paschal Full Moon is the first full Moon after the spring equinox. Also called the Egg Moon, this Moon sometimes occurs in March and sometimes in April.

The word Paschal means “Passover” in Greek (a transliteration of the Hebrew word “pesach”). This Moon is significant because it is used to determine what date Easter will fall on each year. This is why Easter is a movable holiday, occurring anywhere from late March to late April.

Just to make things more complicated, the date of the Paschal Full Moon may not always coincide with the actual full Moon. In fact, it can differ by as much as two days. That’s because, rather than being tied to an actual astronomical event, ecclesiastical authorities the middle ages decided that the Paschal Full Moon would fall on the 14th day of the lunar month beginning after the spring equinox, known as Nissan in the Hebrew Calendar. That day roughly corresponds with the time of the full Moon, and the two overlap more often than not.