Went to church on Ash Wednesday to get my ashes and couldn't help but notice the diversity among the parishoners here in Plano. Our fair town has a very homogeneous image, but I saw people with all kinds of different hair colors. That's a start, isn't it?

Anyway, it isn't just that Lent

*seems*early this year, it actually

**is**early this year. Last year Ash Wednesday was on February 26th. You see, Ash Wednesday is 46 days before Easter, and Easter is the first Sunday after the first full moon that occurs on or after the vernal equinox. Except that we aren't really talking about the astronomical vernal equinox or the astronomical full moon, but the ecclesiastical ones. There is a table maintained by the Church that defines the ecclesiastical full moons, and the ecclesiastical vernal equinox is

**always**on March 21.

No, these aren't the same tables used by Astrologers.

What? You don't have access to the church lunar tables? Well, you're in luck. Some geek named Oudin had

*way*too much time on his hands back in 1940 and came up with the following set of equations to compute the month and day of Easter using only the year, y, as input.

Gene, put down your hand. Yes, Gene, I see the 19 times y divided by 19. No, that isn't the same as y. Why? Because these are allc = y / 100

n = y - 19 * ( y / 19 )

k = ( c - 17 ) / 25

i = c - c / 4 - ( c - k ) / 3 + 19 * n + 15

i = i - 30 * ( i / 30 )

i = i - ( i / 28 ) * ( 1 - ( i / 28 ) * ( 29 / ( i + 1 ) )

* ( ( 21 - n ) / 11 ) )

j = y + y / 4 + i + 2 - c + c / 4

j = j - 7 * ( j / 7 )

l = i - j

m = 3 + ( l + 40 ) / 44

d = l + 28 - 31 * ( m / 4 )

*integer*operations. That means that you throw away any fractional parts.

Let's work through a bit. This is 2005, so y = 2005. We immediately compute c to be 20.05, but since we're doing integer division we throw away the .05 and are left with c = 20. Still with me? Good. Plugging 2005 into the equation for n gives us

After doing the integer division shown inside the parentheses we getn = 2005 - 19 * ( 2005 / 19 )

And that is clearly 10.n = 2005 - 19 * 105

If you are determined you can finish the calculations (be careful with your precedence rules) and figure out that Easter will fall on March 27th this year. At least for the Roman Catholic Church and the Protestants. Yes, the Protestant churches, even the Suthren Babatists, follow the Pope's rules on this one.

Hope you've all recovered from the Mardi Gras celebrations. And speaking of Mardi Gras, you can figure it out from Easter as well. Once you know when Easter is you count backwards 47 days and you find yourself on Mardi Gras.Shallow Thought #1:Do I have to read phishing emails on Fridays in Lent?

No, they don't give you beads if you go to church on Mardi Gras.

## 1 comment:

love the "Shallow Thought #" item. well done, Obi Wan.

As to the Easter calculation, I always thought

The Calculuswas involved. You know .. integer xdx,yadda yadda yadda.Post a Comment