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Prof. Sam LawlerRE: https://telescoper.blog/2026/04/03/finding-easter/
I'm an astronomer, and I teach at a Catholic college (though I'm not religious myself).
I had absolutely no idea how complicated the date of Easter is. Wow.
MsMerope@sundogplanets what's so complicated about "the first sunday, after the first full moon, after the vernal equinox" ??? ๐คช
(I've had to explain it so many times I have it memorized)
Louis A. M. ๐จ๐ฆ@MsMerope @sundogplanets That's what they were aiming at, but theorists built a table to calculate Easter. That's where it gets complicated!
๐ https://en.wikipedia.org/wiki/Date_of_Easter#Calendarium
EyeI never understood why it always changes.
Riley S. Faelan@grb090423 Backwards compatibility. It's tied to a Jewish holiday, and the Jewish lunisolar calendar is built radically differently from the solar-dominant Roman calendars that grew dominant in the Christian parts of Europe.
Thank you for explaining this. I did not know ๐๐
@grb090423 You might also find this tidbit intriguing: https://toot.cat/@riley/116249726406937771 @sundogplanets
I did. Thanks! ๐๐
@grb090423 In the early days of the Christianity, the Easter date could be determined in Rome, and just, effectively, mailed to wherever there were Christian congregations. But by the late 400s / early 500s, the Roman Empire was in such a delapidated state that reliable mailing started to be an increasing problem, so various offline methods for the Easter determination were considered. The officially adopted one was eventually based on an algorithm developed by one Dionysios Exiguus, or Dennis the Geek, potentially partly because of its another important benefit: it allowed the steps to be unambiguously independently verified, and mistakes caught. (There were a couple of embarrassing mistakes in some Easter tables that the early Popes published. Big scandals in their days, because holidays were Serious Business. Literally.)
You are educating me! I can definitely say TIL.
Dennis the geek... Is that real?!
Do you know so much about this because you have studied it?
It's sort-of real. 
Dionysios was once a popular Greek name, derived from the name of the ancient Greek deity of drinking and being merry. The modern English Dennis is an adaptation of it, the same way a lot of modern English names are adaptations of Greek names poularised by Christianity's spread. This particular Dionysios was a monk known for being small and humble ('Exiguus' literally means 'Humble'), and, well, also for enjoying computing things. Hence, I submit that 'the Geek' is a defensible translation of his Greek nickname. 
I know these things because Knuth's The Art of Computer Programming includes a passage about the Computus, as an example of an early elaborate algorithm, and, being an #ADHD kid, I promptly descended into the rabbit-hole.
This is great!
And I agree, Dennis the Geek should absolutely be accepted ๐๐
Thanks so much for widening my knowledge today! I didn't know any of this ๐
Ken Butler@riley @grb090423 @sundogplanets I didn't know he was called Dennis (sorry).
Anyway, thanks for sharing.
@nxskok He probably wasn't, in his days. He lived in the 'Civilised World'(tm); the still-chugging-on Roman Empire, where both Greek-speaking Romans and Latin-speaking Romans would have used some recognisable form of 'Dionysios' or 'Dionysius'. The 'Dennis' form probably only arose as the name got exported into the 'Barbarian World', probably starting from the semi-"wild", semi-Roman, Gaul of the day, where the two had some of the relatively friendliest encounters. Old Greek is a bit weird, as languages go, in that it has a marker suffix for the nominative case; most other European languages don't, and as the Greek and Latin words started to seep into the developing European languages, many of them kind of bulk-snapped the -os and -us nominative suffixes off from Roman words, and names. With that, and some vowel merging, Dionysios became Dennis for English (and Denis / ะะตะฝะธั for Bulgarian). It's the same process that made 'Mathaios' into 'Matthew', 'Petros' into 'Peter', and 'Ioannes' into English 'John' and German 'Hans' and Slavic 'Ivan'.
@riley @grb090423 @sundogplanets thank you for the much better explanation than I deserved after all I did was almost-quote a line from Monty Python and the Holy Grail.
always tired@riley @grb090423 @sundogplanets
Though it doesn't always (nearly) coincide with Pesach.
Jim Daly@sundogplanets In modern Irish the word for computer is 'rรญomhaire', which derives from the Old Irish 'rรญmaire', which was someone (a monk) who computed things such as the position of celestial bodies and the timing of Easter. https://www.ria.ie/2020/03/05/inside-a-history-of-ireland-in-100-words-riomhaire/
mark ๐ฎ๐ช ๐ช๐บ@psneeze The Latin word for the process of figuring out when holidays were was 'Computus'. In theory, the sub-process of figuring out when Easter is is supposed to be the more specific 'Computus Paschalis', but in practice, that was the most important of all the Catholic Computuses, so 'the Computus' tends to refer to just that one.
@riley Fascinating. If the etymology had taken a different twist I could well be typing this on an Eastering machine. @sundogplanets
@psneeze Yep. Or the Rising Machine.
@riley ๐ฎ Yes! @sundogplanets
@psneeze Oh, and there's a famous book by Isaac Asimov in which 'Computer' is a job title for humans, and not even by clever pun: The End of Eternity. In it, The Eternity is an organisation for manipulating Teh One Timeline, and it employs people known as Computers to figure out which way the timeline should be manipulated. Computers as we know them are notoriously missing from throughout the book (except, possibly, a seldom-referenced hand-held device that might be interpreted more like a PDA or a calculator), which kind of makes sense, because the book came out in 1955, when the early ancestors of our kind of computers were exotic experimental mathematics things that militaries sometimes gave maths departments a lot of money for.
@riley Computers is what NASA called the mathematicians (mainly women) who did the calculations for space flight so I suppose Asimov was influenced by that. @sundogplanets
@psneeze There was no NASA in 1955. It was still two years until the Sputnik Moment that caused NASA to be established.
@riley Maybe I'm confusing it with the NACA. @sundogplanets
@psneeze Maybe. I don't know for sure, but NACA would probably have been into some fancy fluid dynamics calculations by its latter years, and a systolic array of human computers is a feasible way of doing it.
Incidentally, a major plot twist of the book is that future humans find it to be a problem that the early Eternity's meddlement didn't let Terrans develop space travel technologies.
@psneeze I don't know for sure, but Asimov's inspiration might have been the Manhattan Project's practice of arranging human 'computers' into systolic arrays to perform complex simulations before the time of automatic computers and spreadsheets. Reportedly, these computers could use mechanic calculators, though.
The Manhattan Project's practice might, in turn, be derived from the New Deal initiative of the "Mathematical Tables Project", which employed unemployed office clerks and tasked them to 'compute' look-up tables for a bunch of useful transcendental functions. Importantly, the Tables Project was relatively public from the beginning; the Manhattan Project, obviously, was very, very classified, in order to properly ensure that only Russian spies would know exactly what was going on in it. But ten years after the war, the organisational lessons of the project might possibly have started to seep out of the military.
@sundogplanets Most of the complexity is because it needed to be backwards compatible with the Hebrew calendar, really. Backwards compatibility has a tendency to make simple things hard like that.
@sundogplanets oh there has been LOTS of ink spilled on this topic. I live not far from where the Irish Celtic Church (was forced to) accepted the Roman/Nicene system. https://en.wikipedia.org/wiki/St_Laserian's_Cathedral%2C_Old_Leighlin
Szescstopni@sundogplanets Even more complicated on Mars. Yes, this is a real paper in a real journal, though not one I would trust in any respect (the paper is in Polish, but there is an English abstract)
David Fi&er@sundogplanets My favourite part of the Wikipedia page about calculating the date of Easter is when the church elders finally got embarrassed about having to ask their Jewish neighbours when Passover was and started to try to figure it out on their own.
Anarchist Trans Ace Pirateto be fair, all things Catholic are complicated
Roy -- the dull oneThanks for illuminating this!
I remembered from childhood education that the date of Easter was determined by some mysterious calculus, performed in some faraway place by some select cognoscenti using some ancient methodology that little boys in the backwoods of North Carolina will never be able to master. I also learned that I should not waste time on things I can't influence and don't care enough to understand. Now I just look at the calendar and the problem is solved!
@oldclumsy_nowmad @sundogplanets My grandmother had something called the Book of Common Prayer (Church of England) and it was all spelled out in the back of there.
Ed Wiebe@sundogplanets The date. The bunnies. The eggs. The rising from the dead. It would be a challenge to make Easter less Christian than it already is.
Pino Carafa@sundogplanets What shocks me most of all is how the dude was born at Christmas and they nailed him to a cross 4 months later.
Katzedecimal
Samantaz Fox@rozeboosje @sundogplanets Wait till you learn that he was likely born in 5 BC :D
@SamantazFox @sundogplanets I thought he was imaginary ๐ค
G ๐ฎ๐น@sundogplanets first sunday after first full moon after 25th march ... Easter is a holy day for procrastinators ๐ I'm not religious either, I think I learned that in my 40s
Will Deakin@sundogplanets Hilda of Whitby says "hold my beer"
"Bede present[s] the synod as a victory for the Roman party...[but doubted their use in Rome]. He produced his own version based on the Alexandrian tables, as amended by Dionysius...in his De Temporibus (703) and in more detail in his De Temporum Ratione (716โ25). The Bedan tables came to be accepted in the British Isles and the Carolingian Empire in the ninth century and in Rome in the tenth."
https://en.wikipedia.org/wiki/Synod_of_Whitby
The Lady (La Donna)@sundogplanets
I attended a Catholic College and work for a Catholic organization. Glad they aren't offended that I question .... nearly everything.
I attended a Catholic College and work for a Catholic organization. Glad they aren't offended that I question .... nearly everything.
Eggs now in different baskets.@sundogplanets Perhaps more bizarre is that in Norway the deadline to take studded tyres off your car is the week after Easter.
Which is completely daft as the dates that Easter can fall on is in a range of a month.
The weather here can vary enormously between late March and late April.
We just had two nights where snow fell. It would make a lot more sense to just pick a date that reflects the change in the weather such as the 15th of April for the deadline.