I know that there are 35 possible days which can be Easter Sunday, but over the millennia, has the distribution been consistent across all 35 dates? Is there a one in 35 chance that any Easter will be on 4/20? Or does the dance of the earth and the moon mean some dates are more likely than others?
I’m not sure about millennia, but this page shows the distribution from 1600 to 2099 (i.e., a sample size of 500 years), and no, it’s not been/will be evenly distributed.
Occurrence on the earliest possible dates (March 22-25) and latest possible dates (April 23-25) are much lower. Even among the other dates, there are a few (March 31, April 5, April 11, April 16), which have happened a bit more often.
Technically, my birthday (March 24) can be Easter, but as a kid, I was saddened to learn that the last time it happened was 1940, and would not happen again until 2391.
The date of Easter is set as “The first Sunday after the first full moon after March 21”. So you’ve got three different cycles (the yearly cycle, the lunar cycle, and the weekly cycle). These three cycles are unrelated to each other, with the ratio of any two of the periods being presumably irrational, so averaged over all of time, where you are in each cycle is essentially random with respect to each other.
So basically, every year has a March 21. Then, roll (approximately) 1d28 to determine where you are in the lunar cycle, and then roll 1d7 to determine where you are in the weekly cycle.
Wikipedia has some nice charts, in addition to what @kenobi_65 posted.
Here is one for the entire 5.7million year cycle: Date of Easter - Wikipedia
It is exceedingly complicated.
Surely, there are only four possible Sundays - or is it five?
Yes, but any of those sundays could be any date between March 21 and April Whatever.
That’s a great visual.
One of the fascinating things about that chart is that distribution of the occurrences from March 28th through April 20th is pretty consistent, at about 3.4%…except for April 19th, which is nearly 4%.
I was always told Easter was the first Sunday after the first full moon after the Vernal equinox which is not always on March 21.
My birthday is April 11 and Easter was on my birthday in 1971, 1982, 1993 and 2004. Then when I’m getting in the groove, it jumps to 2060 which is the 100th anniversary of my birth. I expect many presents and Peeps.
That was mine understanding as well. The date of the vernal equinox is kept approximately, but noncontinuously, constant with leap days. So that puts in another 400-year cycle.
That Dionysius Exiguus was a real card, wasn’t he? 
But it appears the actual computation uses a simplified lunar cycle and a simplified equinox rather than the actual astronomical phenomena. Cheaters! 
Oh, I had a nasty case of simplified equinox about 3AM this morning. I blame week old spaghetti for dinner. 
That was the reason for the Gregorian reform: the vernal equinox and the calendar days were getting out of synch over the centuries.
When everyone calls you Short Dennis to your face, you develop either a sense of humor or a scarcely-suppressed murderous rage. Or both.
Yes… like I said it’s extremely complicated because the math is based on historical comprises, changes in the calendar (Gregorian v. Julian) and various “cheats”.
Gauss had an interesting algorithm you can read about here: Date of Easter - Wikipedia
The key point there is the special cases at the bottom:
That second one is what makes April 19th overrepresented, and April 26 not appear at all.
I can’t actually follow most of it, but the key seems to be some agreement made a long time ago:
No, I don’t think that’s right. It is defined based on the “paschal full moon”, which is based on the “ecclesiastical equinox” which is fixed at March 21. And this “paschal full moon” doesn’t have to actually be a full moon - it’s just a computation.
It is always going to be a simplified computation unless the church decides its calendar is going to be fixed to the actual astronomical phases of the moon and Earth’s orbit. The same may be said for the Jewish computus.
My birthday ends up during Passover every few years. Flourless birthday cake is disappointing.
are all flours forbidden for you? I looked it up, and rice and corn flour are sometimes permitted. I’ve had some very good rice flour cakes.