Determining the date of Pascha

[Jason H.]

I was curious as to how Orthodox decide the date for Pascha. It was recently brought up at an OCF meeting about how the heterodox use their predicitions for "Easter" but then I realized that I ahd no clue as to how we use it; and i've been Orthodox since 2006!

Could someone please enlighten me on this.

With humility,

Jason H.

[Herman Blaydoe]

As good an explanation as any can be found here: Paschal Date Calculation (http://www.covert.org/paschaldate.html)

[Dimitris]

Let's take for example the year 2012: spring starts on 20th March, first full moon of spring is on 6th April, the following Sunday is 8th April. Considering Christian Pascha has to be after Jewish Passover, which happens to fall on 7th April, Easter Sunday should be 8th April. Nevertheless we celebrate it one week later, on 15th April. Why is that? Shouldn't it be fixed?

[Jason H.]

Herman,

Now ith extreme humility I still quite don't understand how it works. *place dunce cap on head*

[Father David Moser]

Easter Sunday should be 8th April. Nevertheless we celebrate it one week later, on 15th April. Why is that? Shouldn't it be fixed?

At the time when the typicon was established the whole Church used the Julian (Old) Calendar. The dates of the spring equinox and full moon were found to repeat in a certain repeating order. This order was codified in a written table so that one did not need to be able to have astronomical expertise to determine the date of Pascha, rather it was calculated according to the pattern codified in the table. Since that time the astronomical calendar has varied sufficiently from those observations such that the sun and moon no longer determine the date of Pascha directly, but the dates are "fixed" by the table of dates given in the typicon. (and so in one sense Pascha is fixed already - its just that the dates of its variation is fixed rather than fixing it to a single date)

Fr David Moser

[Michael Stickles]

Let's take for example the year 2012: spring starts on 20th March, first full moon of spring is on 6th April, the following Sunday is 8th April. Considering Christian Pascha has to be after Jewish Passover, which happens to fall on 7th April, Easter Sunday should be 8th April. Nevertheless we celebrate it one week later, on 15th April. Why is that? Shouldn't it be fixed?

To expand on Father David's post, the current Orthodox calculation uses a 19-year repeating cycle (http://www.assa.org.au/edm.html#OrthCalculator) of what is called the "Paschal full moon". This is used instead of the observed full moon after the observed vernal equinox. In 2012, the Paschal full moon occurs on March 29 of the Julian calendar, which is April 11 on the civil calendar. The next Sunday is April 15.

There is a reason why this is done instead of using the actual astronomical events. Take 2001, for example. The vernal equinox occured on March 20; the first full moon after this occured on Sunday, April 8. So, using direct observation, Pascha would have been on April 15, the following Sunday. However, since the full moon occurred at 03:24 GMT, it actually occurred late on April 7 in the U.S., meaning over here we would have celebrated Pascha on April 8. A formula avoids those kinds of discrepancies (just "picking a place" for dating the equinox and full moon would do that too, but then you'd have "political" considerations over the choice of place - Greenwich? Constantinople? - and those are best avoided as well).

There is a discussion of the early history of Paschal calculations (http://www.ccel.org/ccel/schaff/npnf214.vii.xi.html) in Schaff's The Seven Ecumenical Councils. It's a little shorter on details than I'd like, but still interesting.

In Christ,
Michael

P.S. - Jason, check out my link above to the 19-year cycle discussion - I think it might be easier to follow, since they use tables instead of math, making the patterns easier to see.

[P.Tsiros]

these are the calculations

b = year % 4; calculate the remainder of year/4 , excel has the function mod(dividend,divisor) for this
c = year % 7;
d = year % 19;
e = 19 * d + 16;
f = e % 30;
g = 2 * b + 4 * c + 6 * f;
b = g % 7;

days_after_31_mars = f + b + 3 ;

orthodoxs must know mathematics !

[Jason H.]

these are the calculations

b = year % 4; calculate the remainder of year/4 , excel has the function mod(dividend,divisor) for this
c = year % 7;
d = year % 19;
e = 19 * d + 16;
f = e % 30;
g = 2 * b + 4 * c + 6 * f;
b = g % 7;

days_after_31_mars = f + b + 3 ;

orthodoxs must know mathematics !

My math professor would be impressed with this. I would share it with him but I couldn't even begin to understand how to speak it.

[Demetrios Galanidis]

these are the calculations

b = year % 4; calculate the remainder of year/4 , excel has the function mod(dividend,divisor) for this
c = year % 7;
d = year % 19;
e = 19 * d + 16;
f = e % 30;
g = 2 * b + 4 * c + 6 * f;
b = g % 7;

days_after_31_mars = f + b + 3 ;

orthodoxs must know mathematics !

Very impressive first post.

[Dimitris]

There is a reason why this is done instead of using the actual astronomical events. Take 2001, for example. The vernal equinox occured on March 20; the first full moon after this occured on Sunday, April 8. So, using direct observation, Pascha would have been on April 15, the following Sunday. However, since the full moon occurred at 03:24 GMT, it actually occurred late on April 7 in the U.S., meaning over here we would have celebrated Pascha on April 8. A formula avoids those kinds of discrepancies (just "picking a place" for dating the equinox and full moon would do that too, but then you'd have "political" considerations over the choice of place - Greenwich? Constantinople? - and those are best avoided as well).
Well, if that sould be the only reason, then I can't imagine anyone would not agree to take Jerusalem as reference place.

[Michael Stickles]

I can't imagine anyone would not agree to take Jerusalem as reference place.

I wish I could say the same, but unfortunately, I can imagine it quite easily.

[Fr Raphael Vereshack]

I had never realized the importance of having a notional dating for Pascha was until I read of it in this thread. It seems a very important point. Perhaps this also was in the mind of the Church in the centuries when the Church stretched from Britain & Ireland in the west to present day Iraq & Iran in the east. Although the day itself of course slowly shifts in time as you go east and west. But how else could you have a basic unity of date for Pascha except by using a notional dating for it?

In Christ- Fr Raphael