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Calculating the Date of Easter
Posted by
kdawson
on Sun Mar 23, 2008 01:31 PM
from the computus-giganticus dept.
from the computus-giganticus dept.
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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Metric School Terms (Score:5, Funny)
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 (Score:5, Interesting)
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Re: (Score:3, Funny)
Ah! The march of progress. Hasn't happened in the north-west yet, to my knowledge...
Only this year. (Score:5, Funny)
Next year it will be April again though.
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Re:Metric School Terms (Score:5, Informative)
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.)
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Re:Metric School Terms (Score:5, Funny)
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Re: (Score:3, Interesting)
The Council of Whitby resolved this, supposedly.
Re:Metric School Terms (Score:5, Informative)
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Spring equinox (Score:5, Interesting)
It sounds so much more Pagan my way.
Re:Spring equinox (Score:5, Informative)
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In Perl (Score:5, Informative)
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);
};
In PHP (Score:3, Interesting)
hmm (Score:3, Interesting)
Recommended Reading (Score:5, Interesting)
Stupid *nix Tricks (Score:5, Funny)
Calendars are funny things.
Catholic Easter != Orthodox Easter (Score:5, Interesting)
Here's a web site that is more, um, shall we say, enlightened: http://www.assa.org.au/edm.html [assa.org.au]
One of the main differences between the calculations for Roman Catholic Easter and Eastern Orthodox Easter is in which calendar (Gregorian or Julian) is used. Use Google. It's actually quite interesting because of all the history and politics involved. It's not just simple (eg, exactly when is the moon full? over which point on the earth?) as one might think.
Re:Why would (Score:4, Insightful)
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Re:Why would (Score:5, Insightful)
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Re:Why would (Score:5, Funny)
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Re: (Score:3, Informative)
Now of course you have to assume the bible is giving accurate measurements, which is doubtful, so this argument is fairly bunk (even to an atheist such as myself).
Re:Why would (Score:5, Interesting)
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Re:Why would (Score:4, Interesting)
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Re:Why would (Score:5, Funny)
Save the earth! It is the *only* planet with chocolate!
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Re:Why would (Score:4, Insightful)
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Re:how is it... (Score:5, Funny)
There, now it's an official Science article.
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Re: (Score:3, Funny)
Re:how is it... (Score:5, Insightful)
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Re:how is it... (Score:4, Funny)
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.
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Re:how is it... (Score:5, Interesting)
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.
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].
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Jewish, not Pagan, and especially not Druid (Score:5, Interesting)
If you want to say that Passover's date is set at spring pagan holiday time, you'll need to argue with your rabbi or maybe Lehrhaus Judaica about whether your druids are at all the same kinds of pagans as Caananites were. And if you want to say that the name "Easter" and the bunnies and and eggs and marshmallow chickens are ripped off from Germanic spring fertility goddess stuff, you'll have a tough time getting anybody to argue the other side except maybe some atheists who'll say that the Germanic fertility goddess folks ripped that off from nature, which provided the bunnies and eggs, or from the chemical industry who brought us marshmallow peeps.
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Re: (Score:3, Informative)
Re: (Score:3, Interesting)
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 m
Re:how is it... (Score:4, Interesting)
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Re:how is it... (Score:5, Informative)
Even worse... there are Christian women on /.
Seriously, do you assume that all Christians are no-brain idiots who think dinosaur skeletons are an atheist conspiracy? Donald Knuth is a Lutheran, Gregor Mendel was an Augustinian monk, Copernicus was a priest, as was Georges Lemaitre. Lord Kelvin and Max Planck were committed Christians, Arthur Stanley Eddington was a Quaker... There are more here: http://en.wikipedia.org/wiki/List_of_Christian_thinkers_in_science [wikipedia.org] (Not all of those in this list were Christians throughout their lives, but the ones I've named were/are.)
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Re: (Score:3, Funny)
Re: (Score:3, Informative)
Of course, the person in question probably has no idea where the term Fundamentalist comes from in modern Christian terms, so their Worldview on the issue is most likely to be entirely based in the media. Yes, the very media from which science should not be learned either.
Or, "Fundamentalism
Re:It's not even accurate ... (Score:4, Insightful)
> contrary to the ignorant ramblings preached from pulpits every weekend.
You fail Critical Thinking 101.
You can't get an "ought" from an "is". See http://en.wikipedia.org/wiki/Is-ought_problem [wikipedia.org]
The fact that certain behaviors among animals can be observed in nature doesn't imply any moral (or amoral) imperative among humans. There are lots of things animals do that no one would consider OK for humans to do.
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Re:Huh. (Score:4, Informative)
http://en.wikipedia.org/wiki/Easter [wikipedia.org]Wikipedia
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Re: (Score:3, Informative)
You'll find it all on Wikepedia.
Pope decides (Score:3, Insightful)
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
Re:So what day did Jesus die on? (Score:5, Interesting)
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.
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Annual celebrations are arbitrary anyway. (Score:5, Insightful)
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.
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Re: (Score:3, Funny)
Re: (Score:3, Interesting)
Re:666 !!! (Score:5, Interesting)
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.
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Re:666 !!! (Score:4, Informative)
Or, you know, a Jewish or Christian one. The penalty of death by stoning for adultery is straight out of the Old Testament.
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Re:It was a mistranslation. (Score:4, Informative)
Yes and no. In the Hebrew Bible, the word used by Isaiah is rightly translated as "young woman." In the Septuagint (the Greek translation of the Hebrew Bible produced nearly 200 years before Christ, and much older than the oldest extant Hebrew language Bible), however, the word is in fact "virgin."
Many Christians themselves, not to mention those who don't know much about the religion (no offense, but the majority of /.), are unaware of the fact that the Apostles themselves would most likely have used the Greek scriptures--indeed, it is apparent throughout the New Testament that the Hebrew scriptures being quoted nearly all are of Septuagintal origin.
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Okay, but... (Score:4, Interesting)
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Re: (Score:3, Informative)
Yes, the formula by Gauß does. That's one of the reasons the mathematics have to be so fancy.
Re:Birth and death (Score:4, Informative)
For the common man, an easier thing to watch is the moon. The phases of the moon are not only regular, but they're highly visible and uncomplicated. This means that if your calendar has something to do with the moon, then it's not only easy for your astronomers to track, but it's easy to explain to the unwashed masses: just tell them the festival is on the next new or full moon, and they'll know exactly what you mean. You can also track days for a very small number of days; 7, for instance. You can tell people "go out and work really hard for 6 days, and on the seventh, take a break," and most people can do that (and those that can't can just notice that those who can aren't working on some days). In the Jewish tradition, as you're probably aware, the seventh day is called the Sabbath, and is considered sacred.
A mix of the two was popular -- the accessibility of the lunar calendar was nice, but the agricultural significance of a sidereal calendar was needed as well. For the Liturgical year, the calendar starts with the first new moon after the spring equinox. This means that there's not even any pretense that the calendar is equivalent to a sidereal year; the orbital period of the moon just isn't any fraction of the orbital period of the earth.
Easter tries to mix the 3 logical units of measurement: the rules are complicated, but it essentially boils down to finding a date which 1) falls on a Sabbath, 2) comes quickly after an equinox and 3) ties into lunar phase. The way they chose was to set it at the first Sabbath following the first full moon following the spring equinox. But, approximations are applied to make it easier to plan: ancient astronomy was amazing for what they had at their disposal, but really very far from perfect. So, since the need to plan out a major annual festival was superior to the need for people to be able to look in the sky and see it get close, approximations were accepted over time. The "full moon" was assumed to occur 14 days after the new moon, which was in turn predicted from tables generated using an agreed-upon system of reckoning. The equinox was eventually taken to occur on March 21. The end result is that it no longer actually directly corresponds to an equinox or a lunar phase, and is instead based off of approximations that were chosen to make the date easier to work with. Nowadays, the approximation that most proponents of Easter date reform put forth is just to pick something like the first Sunday of April and use that. Others want to go back to a pure lunisolar basis and throw out the approximations. At this point, however, there's not much motivation to do either: we can compute Easter out arbitrarily far now, and it's printed on every c
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