Dear Lent Lookers:
Easter is a little early this year. As you know from my sermon comments yesterday, I am strangely fascinated by the floating nature of this calendar date, tied as it is to the fluctuations between the solar and lunar calendars. The first Sunday after the first full moon after the first day of spring is the traditional statement of the calculation, but of course, that is somewhat confusing because the moon is not equally full across the globe at the same time. As a result, early church calendar calculators (and you think our denomination has too many staff) created what is called the Paschal full moon, a date which has little to do with the actual moon in the sky.
To summarize how that Paschal full moon is calculated, nineteen civil calendar years are divided into 235 lunar months of 30 and 29 days each (the so-called “ecclesiastical moon”). The period of 19 years (the metonic cycle) is used because it produces a set of civil calendar dates for the ecclesiastical moons that repeats every nineteen years while still providing a reasonable approximation to the astronomical facts. The first day of each of these lunar months is the ecclesiastical new moon. The fourteenth day is the ecclesiastical full moon. Exactly one ecclesiastical new moon in each year falls on a date between March 8 and April 5 inclusive. This begins the Paschal lunar month for that year, and thirteen days later is the Paschal full moon. Easter is the Sunday following the Paschal full moon. In other words, Easter falls from one to seven days after the Paschal full moon, so that if the Paschal full moon is on Sunday, Easter is the following Sunday.
Now Passover is a different matter, as the Jewish calendar is a delightfully complicated combination of the solar and lunar calendars, with leap months instead of leap days. It should come as no surprise that there are some subtleties to how the first day of Passover is determined. But worry no longer! This kind of thing can be encapsulated in a handy algorithm which you can find online in a paper titled “Gauss Formula for the Julian Date of Passover.”
While you can, of course, look at an online Hebrew calendar and find out when Passover begins, this paper provides a handy equation to calculate just one specific value: the first day of Passover. And in case you are wondering, since many of us use the Gregorian calendar rather than the Julian calendar, the paper helpfully has code at the end for both cases, adding a correction factor if for some reason you prefer the Gregorian date. I suggest you don’t attempt this formula with pencil and paper—there is a downloadable app.
More simply remembered by the ancients, the first day of Passover is the 15th of the Hebrew month Nisan, but because the lunar calendar does not exactly match the seasons, if the 15th of Nisan falls before the barley harvest, a leap month of Adar II was added to smooth out the difference between solar and lunar cycles.
Whew, aren’t you glad you can just look at a pre-printed calendar?
What makes this interesting to me is how and why this mattered so much to ancient Jewish and Christian fathers. There was something important to having the date mesh with the ebb and flow of nature. It is as if the moon, sun and stars all work in concert to point to the celebration of God’s deliverance. Our spirituality seems significantly more detached from the rhythms of the spheres—we just check our phones.
Suggesting we keep our heads up to see what God may be telling us, I remain,
Jonathan B. Krogh