I'm an astronomer, and I teach at a Catholic college (though I'm not religious myself).
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RE: 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.
@sundogplanets In modern Irish the word for computer is 'ríomhaire', which derives from the Old Irish 'rímaire', 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/
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RE: 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.
@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.
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RE: 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.
@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
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@sundogplanets In modern Irish the word for computer is 'ríomhaire', which derives from the Old Irish 'rímaire', 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/
@psneeze @sundogplanets TIL this !
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@sundogplanets In modern Irish the word for computer is 'ríomhaire', which derives from the Old Irish 'rímaire', 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/
@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.
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RE: 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.
@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)
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I never understood why it always changes.
@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.
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RE: 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.
@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.
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@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
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@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
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@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.
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@psneeze Yep. Or the Rising Machine.
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Thank you for explaining this. I did not know
@grb090423 You might also find this tidbit intriguing: https://toot.cat/@riley/116249726406937771 @sundogplanets
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RE: 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.
to be fair, all things Catholic are complicated
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@grb090423 You might also find this tidbit intriguing: https://toot.cat/@riley/116249726406937771 @sundogplanets
I did. Thanks!
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@grb090423 You might also find this tidbit intriguing: https://toot.cat/@riley/116249726406937771 @sundogplanets
@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.)
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@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?
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RE: 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.
Thanks 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!
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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.
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@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.)
@riley @grb090423 @sundogplanets I didn't know he was called Dennis (sorry).
Anyway, thanks for sharing.
Yes! 
