Every year, I hear someone complaining about how Easter is too late, or Easter is too early. And the number of people that complain about how Easter can't seem to have a fixed date… Every year, I respond to these complaints in the same fashion.
"You do know how Easter is calculated, don't you?"
The blank stares are borderline hilarious.
Easter is always the first Sunday after the first full moon after the Spring Equinox.
(Okay, the Spring Equinox for the Northern Hemisphere.)
It's a simple calculation really, or at least one would assume so, until they discover the truth behind the equation. While the description appears to be one based on astronomical events, it's really not.
The Equinox Calculation
An equinox is the time of year when we have the same number of daylight hours as we do nighttime hours. However, the astronomical equinox can vary from the recognized date by up to two days every year. Notice I said recognized date. The equinox is nominally considered to be March 20th. However, for countries such as New Zealand, this date is actually the date before the astronomical equinox. For American Samoa, it's the date after.
So, Easter is some time after March 20th, depending on when the first full moon is after this date. Yet, this is another descriptor that appears to be astronomically related, but actually isn't.
The Paschal Moon
Easter is based on the Paschal full moon, which is the fourteenth day of the ecclesiastical lunar month. (Isn't that a mouthful to get your tongue around.)
A lunar month can be between 29 and 30 days, intended to approximate the observed phases of the moon. However, a true lunar month, based on astronomical data, varies between 29.27 and 29.83 days. (How confusing can we get?)
The Calculation for Easter
So, for the calculation of Easter, March 20th is the nominated date for the Spring Equinox, and the first full moon after this is some calendar date that is based on a bizarre calculation that approximates the lunar phases—but can get it wrong by up to two full days.
But Easter is always a Sunday.
Let's say that March 20th falls on a Friday, and the Paschal moon falls on March 21st. That means Easter can be as early as March 22nd. However, say the full moon before the equinox fell on March 20th itself. We then need to wait a full 29 days for the next full moon in the calculated sequence. As such, Easter can be as late as April 25th.
It can really do the head in at times.
For 2023, the first full moon after the equinox is on April 6th. The first Sunday after that is on April 9th. So you see, Easter is not early; it's exactly when it should be — even though the way they came to this date is incredibly confusing.
Random Lunar Fact:
January 2018 had two full moons (January 1st and January 31st), and there are two full moons in March 2018 (March 1st and March 31st). The second full moon in a month is known as a Blue Moon.
Because of the Blue Moon in March that year, Easter felt incredibly early (on April 1st, 2018).
February 2018 didn’t have a full moon. A month without a full moon is known as a Black Moon.
The next Blue Moon will be at the end of August 2023. The next Black Moon will be in February 2037.