Yes, I know it’s not my usual posting time of early Monday (or late Sunday for those in the US / Canada), but I just HAD to share this nerdy Easter fun with you. And we can all use a little exercise to work off those choco-calories. (I can, certainly!)
You’ve probably noticed that the date of Easter is a little tricky to predict. It’s not like Christmas or Valentine’s, on the same date each year, nor is it like American Thanksgiving, always the fourth Thursday of November. Instead, it leaps around like a kangaroo on Red Bull.
You may know that Easter is celebrated on the first Sunday after the Paschal full moon, which is the first full moon on or after the Spring equinox (fixed, for convenience, on 21st March).
With me so far? Good. But since the moon will appear different from different parts of the world, the ‘new moon’ was standardised as well, which explains why Passover and Easter are not always the same date. All this resulted in some very lengthy calculations. And, of course, not everyone used the same method, hence the Synod of Whitby to decide whether the English would used the Celtic calculation or the Roman one.
Honestly, maths causes so much trouble!
To simplify matters, they made tables of Easter dates, starting with Hippolytus of Rome in 222. His were based on eight-year cycles, which weren’t very good at keeping pace with the moon. They switched to 84-year tables later that century, and there was even a 532-year cycle at one point, but finally, in the late 4th century, we got the 19-year cycle which we know and love today. (19 years is how long it takes for the solar year and lunar year to get back into step.)
In 1800, mathematician Carl Friedrich Gauss produced an algorithm for calculating the date of Easter in the Julian or Gregorian reckoning. Yes, we changed calendars as well, if it were not already complicated enough.
However a (fairly) simple algorithm was published anonymously in the journal Nature in 1876 and J M Oudin worked out similar one in 1940 using lots of letters to keep track of the numbers. You can find details of it by clicking here. If you prefer a version without the algebra, Michael Hartley has a printable worksheet, a video and even an auto-date-calculator for you. Some service books have instructions for calculating Easter but, although I’m a mathematician, I find these about as clear as the back window of a land rover. Not recommended.
My version (illustrated) is based on Oudin’s method and is similar to Hartley’s, but fits on a sheet of A4.
Click here or on the picture to download the PDF, and exercise your brain to work off all those chocolate calories. You need nothing more than adding, subtracting, multiplying and dividing (the simple version, with remainders).
You put the year in at the top and do the sums, copying the numbers along the arrows where shown, and the month and day of Easter drop out of the bottom like magic.
Oh yes, and …
Christ is Risen!
He is Risen Indeed, Halleluah!
Just a reminder: in a long calculations, multiplies and divides take precedence over adds and subtracts.
Eg, 1 + 2 x 3 = 7, not 9. You’ll only need this once, but I thought I’d remind you. Have fun!
The Reflectionary 