Computus: How the Date of Easter is Computed
2025-3-28
A wise man once said, "Explaining something succinctly does
not mean explaining it so it's well understood." And that
kind of applies to the rule the Roman Catholic church uses to
calculate the date of Easter. Paraphrasing from Wikipedia,
British monk Bede wrote back in 725, "Easter will fall on the
first Sunday following the Paschal full moon."
The Paschal full moon is the first full moon after the Spring
equinox. Therefore, the date range for Easter to fall on is
March 22 - April 25, at least in Catholicism. The Greek Orth-
odox Easter can fall in May because they're still on the Jul-
ian calendar. As such it's outside the scope of this discuss-
ion. Evidently, if the Spring Equinox falls on Fri. 3-20 and
the full moon occurs on Sat. 3-21, the very next day, 3-22,
will be Easter! With that in mind, and just in time for Lent,
let's delve into the earliest and latest Easter dates, as well
as the rarest and find out if any of them have happened/are
likely to happen in our lifetimes.
March 22:
As stated and implied above, the earliest possible Easter is
March 22. But this hasn't happened since 1818! I can safely
say no one reading this was alive then, and for a great many
of you, even your grandparents weren't born yet. And it won't
happen again until 2285 - long after most people alive in 2025
are dead.
March 23:
The second earliest date. Its recency may surprise you. Easter
fell on March 23 in 2008! I remember Ash Wednesday falling in
the dead of Winter, early February, and my mean CCD headmaster
saying "It's quite a bit early this year..." with a smirk. It
was a mild (for March) and sunny Sunday. Most people currently
on Gemini were probably alive for this too. It won't happen
again until 2160.
March 24:
Now THIS is the rarest Easter of all, believe it or not! It last
happened in 1940, which my grandparents were alive and cognizant
for. But it won't happen again until 2391! A difference of over
400 years!
April 25:
This is the latest possible Easter. It last occurred in 1943,
but it will happen again relatively soon - 2038. Assuming shit
doesn't go nuclear by then, most of us alive in 2025 will be here
to see it. After that, it won't happen again until 2190. While
we may never see the earliest Easter, we (probably) will see the
latest.
April 24:
This is 2nd latest Easter, and it last occurred in 2011, just 3
years after the 2nd earliest one ocurred! It won't happen again
until 2095. Some people reading this may very well be alive for
that 2nd latest Easter. If you're not but you made it to 2038,
then fret not! You lived to see the latest possible Easter!
I found a program in C that accurately calculates Easter's date
for any year you give it, and I output nearly a millenium's wor-
th of Easter dates into a text file for your grepping and per-
using. Enjoy!
NOTE: I did not write the aforementioned C program.
Happy Lent, and happy Easter to all!
/gemlog/