Sunday, March 27, 2005

Happy Easter!

Easter, as we know, is celebrated as a moveable feast day. Before the Council of Nicaea in 325 A.D. the date of Easter varied from church to church. Some used a fixed date and others tied the date to the Jewish lunar calendar, depending on Jewish priests to determine the start of the month of Nisan.

In 325 a third solution was agreed on and Easter was determined to fall on the first Sunday after the first full moon after the spring equinox.

By connecting the date of Easter to both the lunar and the solar calendars (which requires fusing a 354-day lunar year with a roughly 365 1/2-day solar year) the bishops created an enormous problem. In addition to needing to correlate the phases of the moon with the orbit of the earth they forced even modern reckoners to confornt a complex and daunting astronomical problem, "one that must compensate for a complicated range of gravitational tugs and pulls from the sun, moon, and other celestial bodies; the slow degradation of the orbits of the earth and moon over time; the slightly elliptical orbits of the earth and moon; and the spin of the earth on its axis -- all factors that Christian time reckoners in the era of Nicaea had no inkling about when they devised their basic formula for Easter." *

Today Catholic astronomers use a 14-step algorithm to determine the true date of Easter, but even this complicated formula is never totally precise. For what it's worth, here is the algorithm (/=division neglecting the remainder, %=division keeping only the remainder, and *=multiply):

a=year%19 [maybe this should now be 20, since we've entered a new century]
b=year/100
c=year%100
d=b/4
e=b%4
f=(b+8)/25
g=b-f+1)/3
h=(19*a+b-d-g+15)%30
i=c/4
k=c%4
l=(32+2*e+2*i-h-k)%7
m=(a+11*h+22*l)/451
Easter month=(h+l-7*m+114)/31 [3=March, 4=April]
p=(h+l-7*m+114)%31
Easter date=p+1 (date in Easter month)

I believe I'll leave the calculations to others! Nevertheless, regardless of your faith or worldview, we wish everyone a happy and joyous day. Though cool and overcast on the island today we know that springtime weather is "just around the corner."

(*Information & quotation about the dating of Easter was taken from the fascinating book "Calendar" by David Ewing Duncan.)

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