Each year, Easter occurs on the first Sunday after the first full moon after the vernal equinox. The calculation for determining the date of Easter is called “Computus,” which is Latin for “computation.” It turns out that that 23.5’ tilt of the Earth’s axis that John mentioned that creates our seasons makes for some complicated holiday planning. Are there any fans of modular arithmetic in the house this morning? You’re in for a treat over the remainder of this sermon!
Reforming the Computus, the method of determining the date of Easter, was actually the major impetus behind the introduction of the Gregorian calendar in 1582. Easter Sunday is the first Sunday after the paschal full moon, which sounds simple enough. But German astrologer and mathematician Christopher Clavius’ tabular method for calculating that date started to be wrong after a couple hundred years, thanks mostly to the fact that a month is actually more like 29.5 days rather than exactly 30 days.
I greatly prefer the algorithmic method of the Computus, introduced by German mathematician Karl Friedrich Gauss, in the year 1800. Gauss’ method uses the number of the year mod 19, mod 7, and mod 4, as well as the floor function applied to the number of the year divided by 100. I will spare you the complete walk-through, but it turns out April 21st is in fact correct for this year, and you can see my work as an appendix to the printed version of this sermon, available in the lobby.
What all of these centuries of computation say to me, is that there really is something special about the first full moon after the vernal equinox! As long as humans have walked this planet and had chronological technology, we’ve been able to feel that specialness, and we have felt spiritually compelled to honor it. The etymology of the word “worship” comes from acknowledgement of that which is worthy, and in this sense, we have throughout our history worshipped the return of Spring.
In ancient Judaism, Passover coincided with the spring harvest and was a pilgrimage festival, and later it commemorated the Exodus from Egypt in the 13th century BC. The Teutonic goddess Ostara and the egg she carries are symbols of fertility, and a popular myth says that the children of her time presented eggs to the goddess as a gift in return for her bringing them the spring. The Celts often dyed the eggs red to symbolize the menstruation cycle and then buried the eggs alongside a seedling to sustain and feed the plant through its growing season. Indeed, we humans have always been able to feel something special about the return of the sun and its warmth to our lives.
That’s the return of the sun, s-u-n. The return of the son, s-o-n, the resurrection of Jesus, has long been a more complicated matter for Unitarian Universalists. William Ellery Channing, in his definitional 1819 sermon “Unitarian Christianity,” described that one of the ways Jesus worked “to rescue men from sin and its consequences (was)… the resurrection, which powerfully bore witness to his divine mission…” Barely 20 years later, however, Theodore Parker rejected the supernatural divinity of Jesus in his sermon “On the Transient and the Permanent in Christianity.” In it, he argued that if we took Jesus’ resurrection literally as a marker of his supernatural status, it became “but a show.” Parker’s rejection of the supernaturally miraculous Jesus later became a definitional aspect of Unitarianism itself.
Seeing Jesus not as a God, but as a human person, makes his achievements all the more special and remarkable. That was Parker’s point, as he emphasized “For if he were not a man, but a god, what are all these things; what his words, his life, his excellence of achievement?” It’s precisely the humanity of Jesus of Nazareth that makes his life such a worthy example. He was born a poor and disfavored human person, who peacefully opposed the Roman empire, giving all that he had to the struggle for liberation, including his life.
Losing Jesus was a terrible blow to his followers who had put so much hope, trust, and faith in him. The struggle for collective liberation is often a bitter one, and losing a leader whose message has broken through is heartbreaking. We can all think of leaders in our lives and in our world who, if we lost them in an untimely manner, much less to crucifixion, we would be racked with despair.
But the message of Easter (pause) is that no matter what happens to our leaders in the struggle for collective liberation, their spirits and their message live on in us. None of us know what really happened to the body of Jesus when his followers returned to his tomb to find the rock rolled away. But we can all identify with the feeling of transitioning from grief and despair to hopefulness and rejoicing. We celebrate the Exodus, and the Resurrection, and the rebirth of flora and fauna at this time of year because in astronomical terms, in the common experiences that unite us as human across time and across cultures, we can’t help but feel something special about that first full moon after the vernal equinox. It will perpetually inspire and energize us. And so we study it, we base our calendars around calculating it, we worship it, and today, we celebrate it. May the special feelings of today, Easter Sunday, carry us forward in doing what needs to be done.
May it be so, and may we be the ones to make it so.
Delivered at Northwest Unitarian Universalist Congregation
April 21, 2019
© Rev. Jonathan Rogers
Easter Date 2019 by Gauss’ Calculation:
(Gauss’ Calculation is that Gregorian Easter is 22 + d + e March or d + e − 9 April)
a= 2019 mod 19 = 5
b= 2019 mod 4 = 3
c= 2019 mod 7 = 3
k= ⌊year/100⌋ = 20
p= ⌊(13 + 8k)/25⌋ = 6
q= ⌊k/4⌋ = 5
M= (15 − p + k − q) mod 30 = 24
N= (4 + k − q) mod 7 = 5
d= (19a + M) mod 30 = 29
e= (2b + 4c + 6d + N) mod 7 = 1
d + e − 9 April = 21 April