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Calculating the Date of Easter

kdawson posted about 6 years ago | from the computus-giganticus dept.

Math 336

The God Plays Dice blog has an entertaining post on how the date of Easter is calculated. Wikipedia has all the messy details of course, but the blog makes a good introduction to the topic. "Easter is the date of the first Sunday after the first full moon on or after March 21... [T]he cycle of Easter dates repeat themselves every 5,700,000 years. The cycle of epacts (which encode the date of the full moon) in the Julian calendar repeat every nineteen years. There are two corrections made to the epact, each of which depend[s] only on the century; one repeats (modulo 30, which is what matters) every 120 centuries, the other every 375 centuries, so the [p]air of them repeat every 300,000 years. The days of the week are on a 400-year cycle, which doesn't matter because that's a factor of 300,000. So the Easter cycle has length the least common multiple of 19 and 300,000, which is 5,700,000 [years]."

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336 comments

Metric School Terms (4, Funny)

26199 (577806) | about 6 years ago | (#22837672)

In the UK the academic year is split according to the date of Easter. I recall hearing about an effort to move to a "metric" system which doesn't depend on Easter. This suddenly makes a lot of sense...

Re:Metric School Terms (5, Interesting)

Corsix (1178253) | about 6 years ago | (#22837826)

My school (south-west UK) seems to have detached term times from Easter. This is Easter weekend at the moment, so we get the Friday and Monday off as they are bank holidays, but the two week long "Easter break" isn't for another two weeks yet.

Re:Metric School Terms (2, Funny)

26199 (577806) | about 6 years ago | (#22837872)

Ah! The march of progress. Hasn't happened in the north-west yet, to my knowledge...

Re:Metric School Terms (1)

CSMatt (1175471) | about 6 years ago | (#22837894)

You guys get two weeks off? Lucky Brits.

Re:Metric School Terms (4, Informative)

26199 (577806) | about 6 years ago | (#22837924)

In the UK school is split into three terms ... in the middle of each, you get a week off, and between them, you get two weeks off. Except over the summer when it's six weeks.

So there's more holiday through the year, but the summer vacation is shorter.

(This is probably because we don't have as much summer.)

Re:Metric School Terms (2, Informative)

Anonymous Coward | about 6 years ago | (#22838204)

Yeah, those of us above school age also get a statutory 28 days paid holiday. Which seems a lot compared to the US 11 or 12(?) but if you think that's good I believe the Dutch get 35 days and every 2nd Friday. To take it to the extreme the French are forced to work at most on 35 hours [thedailymash.co.uk] and get four weeks but have to take them in August. Hurrah for the EU!

Re:Metric School Terms (4, Funny)

Foobar of Borg (690622) | about 6 years ago | (#22838494)

Yeah, those of us above school age also get a statutory 28 days paid holiday. Which seems a lot compared to the US 11 or 12(?)
I think 11 or 12 days is about what Americans in the professional class wind up getting on average, but *statutorily* we get somewhere between jack and shit.

To take it to the extreme the French are forced to work at most on 35 hours and get four weeks but have to take them in August.
So basically, if you want to invade France make sure to do it in August. That way, they won't notice until they come back from vacation :-).

Re:Metric School Terms (2, Interesting)

acroyear (5882) | about 6 years ago | (#22837938)

could be worse. In the early 600s, Easter as calculated by Patrick's Irish/Celtic church was on a different day some years than the Roman church. In one particularly odd incident, the King of Northumbria celebrated Easter on a different day from his wife.

The Council of Whitby resolved this, supposedly.

Funny?! (1)

26199 (577806) | about 6 years ago | (#22837948)

Er, mods ... I was being completely serious.

Do not laugh at us! Or we will become more powerful than you can possibly imagine...

how is it... (2, Insightful)

MousePotato (124958) | about 6 years ago | (#22837696)

This is not a science article. Arguably it is a math article to the interested christians on /. but certainly not science.

Re:how is it... (4, Funny)

Otter (3800) | about 6 years ago | (#22837744)

Calculating the Date of Easter Finds Possible Cure For Cancer

There, now it's an official Science article.

Re:how is it... (2, Funny)

popmaker (570147) | about 6 years ago | (#22837866)

Yep, it goes along with the article on how to find out which weekday "seven days before yesterday" is without using your fingers.

Re:how is it... (4, Insightful)

Otter (3800) | about 6 years ago | (#22838022)

Your grasp of astronomical chronology far exceeds mine, then. I'm not a Christian and have no interest in the holiday per se, but thought this article was a fascinating piece of science history, and certainly learned more science from the underlying astronomy and the computation thereof than I would have gotten from any ten Roland Piquepaille rehashings of press releases he doesn't understand.

Re:how is it... (3, Funny)

CRCulver (715279) | about 6 years ago | (#22837764)

Arguably it is a math article to the interested christians on /.

Methinks many families that profess no especial religion nonetheless buy their children bunny figures, chocolate, and disgusting gelatin chicks in the springtime. These sort of articles, besides showing Christians when their religious day falls, also explain when to expect such mechandise in your local stores.

Re:how is it... (2, Funny)

ParaShoot (992496) | about 6 years ago | (#22837810)

These sort of articles, besides showing Christians when their religious day falls, also explain when to expect such mechandise in your local stores.
At the rate the appearance of the merchandise moves further and further back from the official date each year, I wouldn't be surprised if the said gelatin chicks turn up sometime this July. Buy now for Easter '09!

Re:how is it... (0, Flamebait)

Usquebaugh (230216) | about 6 years ago | (#22837932)

Actually it has far more interest for druids etc.

Sort of like Christmas being near another pagan day.

 

Re:how is it... (1)

Snorpus (566772) | about 6 years ago | (#22838048)

Gelatin chicks? Chocolate bunnies? Don't kids get real chicks (dyed yellow, purple, etc.) and bunnies at Easter any more?

Re:how is it... (4, Interesting)

Phroggy (441) | about 6 years ago | (#22838300)

Arguably it is a math article to the interested christians on /.

Methinks many families that profess no especial religion nonetheless buy their children bunny figures, chocolate, and disgusting gelatin chicks in the springtime. These sort of articles, besides showing Christians when their religious day falls, also explain when to expect such mechandise in your local stores.

Don't forget about Mardi Gras!

Mardi Gras (Fat Tuesday, Shrove Tuesday, Pancake Day, etc.) is the day before Ash Wednesday, which is the first day of Lent, which begins 40 days (excluding Sundays) before Easter. So, once you've calculated the date of Easter, subtract 47 to get the date of Mardi Gras [wikipedia.org].

Re:how is it... (0, Redundant)

BountyX (1227176) | about 6 years ago | (#22837782)

There's chrisitians on Slashdot? =P

Re:how is it... (3, Interesting)

Stormwatch (703920) | about 6 years ago | (#22838096)

Hey, it's not like religious people are all irrational! In fact, except for fanatics, it's like they have two brains - one to deal with day by day matters, and one for the church things. Which is a good thing, actually. But when you think about... well, it's quite a freakish notion.

Re:how is it... (1)

BountyX (1227176) | about 6 years ago | (#22838416)

Two brains....sounds like a personality disorder to me. No just kidding, I'm a Pastafarian myself.

Please surrender your US Citizenship immediately. (-1, Troll)

Shturmovik (632314) | about 6 years ago | (#22837822)

Only infantile nutjobs are permitted to possess it.

PRAISE THE LORD! HALLELUJAH!

If I can't be bothered understanding something, I'll say [deity/idol/god/prophet] made it that way. Why should I have to psychologically mature beyond the age of two years old? The great bearded, toga-wearing boogeyman floating around in the sky will save us from our sins and prevent us from ever having to accept responsibility for anything!

Re:how is it... (0)

Anonymous Coward | about 6 years ago | (#22837834)

I'm not a Christian but I find this interesting because it reminds me of the kind of assignments we were given in computer science. Of course, the solution wasn't given like this, only a pattern from which we were to figure out an algorythm, and there was no Google back then.

Re:how is it... (1)

CSMatt (1175471) | about 6 years ago | (#22837960)

This is not a science article. Arguably it is a math article to the interested christians on /. but certainly not science.
Which is why it isn't tagged with the "science" tag and the picture of Einstein is missing.

It's not even accurate ... (-1, Troll)

tomhudson (43916) | about 6 years ago | (#22838058)

The idea that we'll still believe in ANY religion in 5,700,000 years is stupid. We won't even be around then. Of course, fundies believe that evolution doesn't happen, and we'll remain as we are "foreveh and evah, world without end, amen pass the plate brothah".

Fundies - the ultimate proof that intelligent design doesn't exist.

Re:It's not even accurate ... (2, Funny)

cheater512 (783349) | about 6 years ago | (#22838374)

I'm actually worried that in 500 years or so, FSM will be the dominant religion. :)

Is anthropology a science? (1)

Kupfernigk (1190345) | about 6 years ago | (#22838106)

If it is (I think it is) then the calculation of the date of Easter is an interesting demonstration of how the patriarchal Jewish religion has in fact got roots in a matriarchal religion, since its calendar is based on a lunar rather than a solar cycle. (I'm simplifying). There are plenty of clues in the OT for the educated - but educating a few Protestant fundies as to the real underpinnings of their religion might hopefully get them thinking, and thinking helps cure ignorance, and curing ignorance helps do things like stop school boards from requiring teaching Creationism. So yes, it is a scientific article.

Re:how is it... (2, Interesting)

wickerprints (1094741) | about 6 years ago | (#22838120)

I'm not Christian and don't observe Easter, but I am a mathematician, and even I found the calculation interesting. In particular, I was interested to see the variety of algorithms used, as well as their relationship to astronomy.

One should not forget that astronomy--and much of science in general--historically were motivated by religious belief, not just in Western Judaeo-Christian cultures, but all cultures. That this is no longer the case speaks to the power of rational thought over pre-rational mythologies; but it is also a disservice to apply a revisionist view towards the origins of science--which was born from our innate human desire to not merely accept the mechanisms of nature, but to understand it.

Why would (-1, Troll)

BlindRobin (768267) | about 6 years ago | (#22837706)

a rational person care about calculating meaningless dates bounded by fairy tales except perhaps as a "Fun With Calendars" exercise ?

Re:Why would (4, Insightful)

sonicdevo (899106) | about 6 years ago | (#22837734)

Just because the date (and what it commemorates) is meaningless to you, is it really necessary to cast all those who do care about it as irrational?

Re:Why would (0, Flamebait)

BlindRobin (768267) | about 6 years ago | (#22838118)

Yes, I'm really given up on tolerance for god-botherers as I find them to be, in the context of their faith, irrational. I was not trying to start an argument, just stating my position vis-a-vis the significance of this particular date relative to any other.

Re:Why would (0, Redundant)

flyingfsck (986395) | about 6 years ago | (#22838140)

Denying that religion is irrational, doesn't make it any less irrational - on the contrary...

Pi will never be equal to three, even though the holy bible says so.

Curious (2, Interesting)

OeLeWaPpErKe (412765) | about 6 years ago | (#22838474)

Just because I'm curious : where does it say that (not that it changes anything about the meaning of the bible if it does indeed say that, but I'm curious nonetheless) ?

Besides, religion isn't irrational : this [economist.com] article gives a few hints on why (note : if you know a bit of stuff about the differences between religions you'll find that while the arguments presented are not about one single religion, they do exclude a lot of religions, in short the article makes a lot of sense when interpreted to a christian context, and specifically compares this christian(-oriented*) belief system to atheism, it states that atheist societies exist for about 20 years while christian communities generally survive for 150 years, with a number of them being older than any reliable records (about 200 years that is))

* -oriented because of 2 facts :
1) some members of other religions are "cryptochristian", ie they believe and practice the principles of christianity, even when in direct contradiction with their stated religion
2) some christians ... (I'm sure you can fill this in, this seems to be a smaller group though)

Re:Why would (5, Interesting)

Wuhao (471511) | about 6 years ago | (#22837748)

Historical significance, for one. The history of time-keeping and astronomy are intimately tied to the need to celebrate religious events; this goes back much before Christianity. It's really a very neat subject, and it's really fascinating how much math developed simply out of a need to know when and how to throw a party for the gods.

Re:Why would (4, Interesting)

BlindRobin (768267) | about 6 years ago | (#22837916)

Agreed, the history of time-keeping is a very interesting and important subject, however, an arcane method of determining the date for a specific holiday belongs in the category of 'curious minutiae' and is in and of it self just an obscure exercise, except for the devout adherents to it's attending myths.

Re:Why would (4, Funny)

flyingfsck (986395) | about 6 years ago | (#22838164)

I don't care about the myths - the chocolate bunnies and eggs are good enough for me.

Save the earth! It is the *only* planet with chocolate!

Re:Why would (0)

Anonymous Coward | about 6 years ago | (#22838260)

Yea, but while the pre-christians most likely celebrated at the spring equinox (the pagan spring festival that would get adopted by the church since it conveniently already was themed around rebirth and renewal) the arbitrary need for Christians to celebrate it on a Sunday makes this whole date thing a bit more complicated (and less logical imho).

Re:Why would (2, Informative)

GvG (776789) | about 6 years ago | (#22838262)

In my part of the world the Monday after Easter is a national holiday. I've actually implemented the Gaus algorithm to compute the date of Easter in multiple programs, to check if people working on a given date were entitled to extra compensation for working on a holiday.

Huh. (1)

CSMatt (1175471) | about 6 years ago | (#22837712)

I always thought it was based on when the Hebrew calendar said the week of Passover was.

Re:Huh. (4, Informative)

sonicdevo (899106) | about 6 years ago | (#22837786)

"Easter is termed a moveable feast because it is not fixed in relation to the civil calendar. Easter falls at some point between late March and late April each year (early April to early May in Eastern Christianity), following the cycle of the moon. After several centuries of disagreement, all churches accepted the computation of the Alexandrian Church (now the Coptic Church) that Easter is the first Sunday after the first fourteenth day of the moon (the Paschal Full Moon) that is on or after the ecclesiastical vernal equinox. Easter is linked to the Jewish Passover not only for much of its symbolism but also for its position in the calendar. The Last Supper shared by Jesus and his disciples before his crucifixion is generally thought of as a Passover meal, based on the chronology in the Synoptic Gospels..."

http://en.wikipedia.org/wiki/Easter [wikipedia.org]Wikipedia

So what is the calculation for Eastern Orthodox (1)

VP (32928) | about 6 years ago | (#22837798)

Christianity?

Re:So what is the calculation for Eastern Orthodox (2, Informative)

johnw (3725) | about 6 years ago | (#22837862)

The same, except they use the Julian calendar where the western Christian churches use the Gregorian calendar. The calculation of the Jewish passover uses actual observations of the moon so that may be different again.

You'll find it all on Wikepedia.

Spring equinox (4, Interesting)

wile_e_wonka (934864) | about 6 years ago | (#22837722)

I've always thought that it is more fun to say the date of Easter is "the first Sunday after the first full moon after the Spring Equinox," rather than March 21st.

It sounds so much more Pagan my way.

Re:Spring equinox (4, Informative)

AndrewRUK (543993) | about 6 years ago | (#22837968)

Only problem is, your way isn't always right, because the date of Easter is always calculated from March 21st even if (as this year) the northern hemisphere spring equinox doesn't fall on that date.

And yet... (1)

ironicsky (569792) | about 6 years ago | (#22837772)

And yet, it doesn't matter the slightest... over 5,000,000 possibilities to when easter will happen, and they all occur within 6 weeks of each other(Last 2 weeks of March, and all of April), all on Sundays... So I look at it as a 1 in 6 chance of knowing when easter will be each year.

Re:And yet... (1)

GISGEOLOGYGEEK (708023) | about 6 years ago | (#22837804)

Totally missed the point ... they're talking about the pattern of the dates easter falls on from year to year. Not the specific date in any given year.

666 !!! (0, Flamebait)

GISGEOLOGYGEEK (708023) | about 6 years ago | (#22837778)

Come on, there must be some way to show that the date of Easter involves the number 666. With all the brutal evil things that have been done in the christian church's name, there has to be!

There's so many lies involving easter, so many people misled that a dead person came back to life when really someone who was almost dead just made a surprising recovery, there's got to be some evil references in this!

I'm so disappointed in this article.

I bet next people will believe that this guy's mother was somehow a virgin, and not just spouting the same lies that every young, newly sexually active woman says when confronted by her parents.

Re:666 !!! (1)

ParaShoot (992496) | about 6 years ago | (#22837840)

Except that the number of the beast is 616 [wikipedia.org], not 666.

Re:666 !!! (1)

GISGEOLOGYGEEK (708023) | about 6 years ago | (#22837940)

Maybe your beast, but freedom of religion protects my delusions as much as yours. My beast which is absolutely just as real and valid as your beast has the number of 666.

He had the number of 69 ... but found that he'd rather just spoon with two of his friends.

Re:666 !!! (5, Interesting)

flyingsquid (813711) | about 6 years ago | (#22838002)

I bet next people will believe that this guy's mother was somehow a virgin, and not just spouting the same lies that every young, newly sexually active woman says when confronted by her parents.

I seriously doubt that Mary went around saying that she became pregnant despite being a virgin, for two reasons. First, everyone would have read between the lines and assumed Jesus was the product of infidelity, then as now. Saying that Yahweh was the real father makes you look like you're not just loose, you're also batshit insane. The cover story would have been that Joseph was the father.

What's far more likely is that the virgin birth is a later addition to the story of Jesus. In comic book terminology, this is a retroactive alteration of the continuity, or "retcon". "Hm... how do we explain the origin of Jesus' amazing superpowers? How is he able to walk on water, cure leprosy, and feed multitudes using a single loaf of bread, if he's just some average Jew? It's just not plausible, our audience will never buy it. I KNOW! We have a special "Origins of Jesus" issue in the Bible, where we reveal that ACTUALLY, Jesus is the son of God! Now, the fact that he has these amazing superpowers makes sense!"

It's exactly like how Marvel went back and created a backstory to explain the origins of the super-powers of the X-men. In the case of Marvel, alien visitors altered the DNA of ancient humans which resulted in mutants like Wolverine. In the case of the Catholic Church, a super-powerful being impregnates Jesus' mom. It's a really ancient theme. If you recall many of Greek heroes, such as Hercules, had gods for parents, which explained why they were so powerful. Achilles was more like the Incredible Hulk, in that exposure to magic (the waters of the River Styx in the case of Achilles, gamma rays in the case of the Hulk) give them their powers. But Odysseus is like Batman- he doesn't have any superpowers, he's just clever.

Re:666 !!! (0, Troll)

GISGEOLOGYGEEK (708023) | about 6 years ago | (#22838064)

Interesting theory, and good analogy to the comic book industry. Both want you to return each week and buy their product, each wants you to become part of a group of people who follow their story, each fights to fill in the gaps to make their stories more complete.

But I wouldn't totally throw off the idea of Mary and family lying to cover her indescretions. Maybe when questioned, her father helped spread the word, being too softhearted to simply kill his daughter by stoning, the way he would have had to if this were a Muslim story.

Tough one (0)

Anonymous Coward | about 6 years ago | (#22837780)

"Easter is the date of the first Sunday after the first full moon on or after March 21... [T]he cycle of Easter dates repeat themselves every 5,700,000 years. The cycle of epacts (which encode the date of the full moon) in the Julian calendar repeat every nineteen years. There are two corrections made to the epact, each of which depend[s] only on the century; one repeats (modulo 30, which is what matters) every 120 centuries, the other every 375 centuries, so the [p]air of them repeat every 300,000 years. The days of the week are on a 400-year cycle, which doesn't matter because that's a factor of 300,000. So the Easter cycle has length the least common multiple of 19 and 300,000, which is 5,700,000 [years]."


Must be a real bummer trying to reconcile all of that with the fact that we have Easter ONCE EVERY SINGLE YEAR.

So what day did Jesus die on? (0, Troll)

88NoSoup4U88 (721233) | about 6 years ago | (#22837794)

I find it quite amusing that the birth of Jesus is pretty much set in stone (at least if I believe that day to be Christmas), but the date of his death (or resurrection) isn't.

I guess even Christians smelled too much bullshit on the whole story, they rather kept it as vague as possible. ;)

Re:So what day did Jesus die on? (1)

icegreentea (974342) | about 6 years ago | (#22837816)

Yeah. But which Christmas? Dec 25 or Jan 7?

Re:So what day did Jesus die on? (0)

Anonymous Coward | about 6 years ago | (#22837884)

Christmas is always December 25. January 6 is Epiphany, aka "Three Kings Day" which commemorates when the stargazers found the little blighter.

Re:So what day did Jesus die on? (1)

AndrewRUK (543993) | about 6 years ago | (#22838070)

Ahh, but a number of Orthodox churches use the Julian calendar [wikipedia.org]. And December 25th in the Julian calendar is January 7th in the Gregorian (for the next 92 years - 2100 will be a Julian leap year, and the difference will increase by another day.)
So, yes, Christmas is always December 25th, but not everyone agrees which day that is...

Re:So what day did Jesus die on? (1)

thomasdz (178114) | about 6 years ago | (#22838052)

Thank-you from someone who celebrates on Jan 7. (and everyone gives me funny looks when I take that day off work)

Re:So what day did Jesus die on? (1)

Ogi_UnixNut (916982) | about 6 years ago | (#22838094)

Thanks as well ! (just wanted to be counted, kind of curious how many of us are here on Slashdot)

Pope decides (3, Insightful)

iknownuttin (1099999) | about 6 years ago | (#22837828)

I find it quite amusing that the birth of Jesus is pretty much set in stone (at least if I believe that day to be Christmas), but the date of his death (or resurrection) isn't.

The date of birth of Jesus was also pulled out of the ass of some Pope. Christian Holidays were set on their particular dates to get medieval folks to stop their 'pagan' rituals and instead celebrate Christian rituals. Christmas:Winter solstice Easter:Beginning of Spring (Ostara now for you Wicans). I'm such a lapsed Catholic I can't remember the Holy days for other celestial events.

Re:Pope decides (1)

BountyX (1227176) | about 6 years ago | (#22837906)

It's well-known that christian holidays took place during the same holidays as their pegan counter parts. Most of Christian Mythology was borrowed from previous relgions--concepts such as "Virgin Birth", "Son of God", and the majority of prophecies (which were also borrowed by the Jews from previous relgions). You end up with one of the most unoriginal and boring religions ever. Christianity succeeded; however, in advancing society by creating a more inclusive group. You could argue that christian created the middle class, a new concept in those days. Too lazy to quote my sources...sorry. Google to confirm ("Christian Mythology" in wikipedia is a start).

And then some.... (1)

iknownuttin (1099999) | about 6 years ago | (#22838046)

You end up with one of the most unoriginal and boring religions ever.

And then some. "Do onto others as you would have them do unto you." - Confucius

Much of the philosophy was borrowed from Taoism and Buddhism and other Eastern thought.

Re:Pope decides (1)

compro01 (777531) | about 6 years ago | (#22837986)

the feast of st. john is right around the june solstice, though i can't find anything happening near the september equinox.

Re:Pope decides (1)

Skeetskeetskeet (906997) | about 6 years ago | (#22837988)

[i]The date of birth of Jesus was also pulled out of the ass of some Pope. [/i] Probably isn't the first time something was pulled from the ass of a Pope.

Re:So what day did Jesus die on? (1, Informative)

Anonymous Coward | about 6 years ago | (#22837926)

The day of his birth is very much not set in stone, certainly not if you ask people of two distinct denominations.

Religious scholars believe Jesus was born some time between 7-4 BC. The date of Christmas, December 25th, was chosen as was a day used by pagans to celebrate their various gods and goddesses, thus allowing Christians to celebrate without drawing too much attention to themselves. Candles and the ubiquitous fish symbol (the one without the feet;-)) are also left-overs of early Christianity's secrecy.

It's not like they kept extensive birth records on the children of peasants.

Why do computer geeks celebrate Halloween on Christmas? Because OCT 31 = DEC 25.

Re:So what day did Jesus die on? (4, Interesting)

pyite (140350) | about 6 years ago | (#22837962)

I find it quite amusing that the birth of Jesus is pretty much set in stone (at least if I believe that day to be Christmas), but the date of his death (or resurrection) isn't.

Yes, it's set in stone on the wrong date. Shepherds were living outside with their flocks when Jesus was born, yet they wouldn't be doing this in December. It's too cold in Israel. In addition, Jesus died on Nisan 14 (the first full moon after the vernal equinox)... not on a Friday year after year.

Annual celebrations are arbitrary anyway. (4, Insightful)

raehl (609729) | about 6 years ago | (#22838166)

Yes, it's set in stone on the wrong date.

Right. Because we have to celebrate everything in exact intervals of one earth-sun-revolution, and only whole-number interval offsets from the time of the original event.

There's no such thing as the 'right' and 'wrong' date. An event happens. Choosing to celebrate that event once a year (where "year" is the amount of time it takes the earth to go around the sun once) is arbitrary in the first place. It would be just as 'right' to celebrate it every 12 moon-earth revolutions, or 2 mercury-sun revolutions.

If you're already going to base your celebration intervals on the convenience of how often one ball of rock revolves around one ball of gas because you happen to live on said ball of rock, you might as well always celebrate something on the 259th day of the year, or the 4th time the 4th day of the week falls in the 11th month of the year, or the 1st 7th day of the week following the vernal equinox.

Getting bent out of shape because the commemoration/celebration of an event doesn't have the same calendar date as the original event - especially when the original event occured in a time period where the calendar you're using didn't even exist - seems pretty silly. Especially when you're celebrating the birth/death of the son of God.

The date IS set in stone. (1, Informative)

raehl (609729) | about 6 years ago | (#22838090)

It's the first Sunday after the vernal equinox.

The problem isn't that the date is not consistent; it's that the date is set using a DIFFERENT CALENDAR SYSTEM.

Happy Zombie Jesus Day! (0, Funny)

Anonymous Coward | about 6 years ago | (#22837846)

What?

WHAT?

leap days? (1)

acroyear (5882) | about 6 years ago | (#22837914)

now, does all that fancy mathematics and statements about the repetition cycle of days include the Leap Year's Lead Day, as well as the fact that it didn't exist the last time this cycle started?

Re:leap days? (2, Informative)

the_other_chewey (1119125) | about 6 years ago | (#22838480)

now, does all that fancy mathematics and statements about the repetition cycle of days include the Leap Year's Lead Day, as well as the fact that it didn't exist the last time this cycle started?

Yes, the formula by Gauß does. That's one of the reasons the mathematics have to be so fancy.

Anyone with tagging power? (0, Troll)

lantastik (877247) | about 6 years ago | (#22837936)

Feel free to tag this one under the whogivesashit category.

Followup article needed (1)

CrazyTalk (662055) | about 6 years ago | (#22838076)

Hope we see a followup article on how Passover is calculated - after all, they roughly conincided at least once 2000 years ago.....

Leap seconds (0)

Anonymous Coward | about 6 years ago | (#22838114)

With a repeat cycle that long, they also need to calculate in leap seconds as well, which means that the repeat pattern is even longer!

Easter? (0)

Anonymous Coward | about 6 years ago | (#22838170)

Easter? The one with the anthropomorphic egg-laying rabbit, or the one with the zombie?

In Perl (5, Informative)

Phroggy (441) | about 6 years ago | (#22838172)

sub GetEasterDate {
  my($year)=@_;
  # http://www.smart.net/~mmontes/nature1876.html
  my $a=$year%19;
  my $b=int($year/100);
  my $c=$year%100;
  my $d=int($b/4);
  my $e=$b%4;
  my $f=int(($b+8)/25);
  my $g=int(($b-$f+1)/3);
  my $h=(19*$a+$b-$d-$g+15)%30;
  my $i=int($c/4);
  my $k=$c%4;
  my $l=(32+2*$e+2*$i-$h-$k)%7;
  my $m=int(($a+11*$h+22*$l)/451);
  my $month=int(($h+$l-7*$m+114)/31);
  my $p=($h+$l-7*$m+114)%31;
  my $day=$p+1;
  return (0,0,0,$day,$month-1,$year-1900);
};

Re:In Perl (2, Insightful)

gimpeh (1209722) | about 6 years ago | (#22838412)

That is not nearly confusing enough. The original alogrithm was clear and concise. Your Perl implementation should therefore cause distress and confusion. You're a shame to the profession.

In Vim Script (2, Interesting)

Anonymous Coward | about 6 years ago | (#22838184)

Only valid between 1583 and 4899

function! s:EasterSunday(year, return_value)

                if a:year 4089
                                return 0
                endif
                let a = a:year / 100
                let b = a:year % 100
                let c = (3 * (a + 25)) / 4
                let d = (3 * (a + 25)) % 4
                let e = (8 * (a + 11)) / 25
                let f = (5 * a + b) % 19
                let g = (19 * f + c - e) % 30
                let h = (f + 11 * g) / 319
                let j = (60 * (5 - d) + b) / 4
                let k = (60 * (5 - d) + b) % 4
                let m = ( 2 * j - k - g + h) % 7
                let n = ( g - h + m + 114) / 31
                let p = ( g - h + m + 114) % 31

                if a:return_value == 1
                                let easterday = p + 1
                                return easterday
                else
                                let eastermonth = n
                                return eastermonth
                endif
endfunction

hmm (2, Interesting)

thatskinnyguy (1129515) | about 6 years ago | (#22838228)

Is it just me or does it seem like anything posted having to do with politics or religion turns into a mod point black hole?

Recommended Reading (4, Interesting)

szyzyg (7313) | about 6 years ago | (#22838264)

I won't hesitate to recommend the book 'Marking Time' by Duncan Steel - it's a great book about the history and evolution of calendars. The date of easter is a particularly interesting question and Duncan goes as far as to explain how the date of Easter was at the core of an English plan to attack the legitimacy of the Catholic church and how this plan was what triggered Britain's first attempts to colonize America, great stuff.

What's the meaning of Easter? (1)

OzPeter (195038) | about 6 years ago | (#22838266)

More East.

*Ta-da-boom*

I first saw this in a Tandberg [wikipedia.org] cartoon years and years ago. PIty I can't find the original.

Incompetent math (0)

Anonymous Coward | about 6 years ago | (#22838280)

> The days of the week are on a 400-year cycle,

The days of the week are on a 7 day cycle. Who told you different ?

There is a 400 year cycle of leap years, but this is an approximation that is usefull for the next few hundred years. It is not known yet whether a further adjustment will be done in the year 3200 or in 3600, that is for them to determine.

As it is not exactly 400 year then using this as a 'factor' of 300,000 is pointless and wrong.

> [T]he cycle of Easter dates repeat themselves every 5,700,000 years.

We have no idea what the cycles will be in that time scale. The Earth may not have 365.24.. days in each year at that time, nor the moon have the same orbit.

Why does easter change every year and... (1)

beaverbrother (586749) | about 6 years ago | (#22838472)

Why does Easter change date every year and Christmas does not. Were they set based on different calendars? Otherwise it would be indeed weird that the number of months between the two days switches all the time.

The Golden Ratio Egg (2, Funny)

bubezleeb (1222938) | about 6 years ago | (#22838476)

Of course, when these calculations consider the addition of the Easter Bunny, the Fibonacci sequence, represented as an infinite mathematical set, must be applied to the cycle result. In the end you'll find it's bunnies all the way down.
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