Date of Easter

Introduction

The problem of finding the date of Easter is not an easy one. The date depends on both the Gregorian calendar (in which there is a leap year every four years, except for century years where only one in every four is a leap year) and the Jewish calendar (which follows a solar cycle for years and lunar cycle for months - it has a 19-year cycle in which the 3, 6, 8, 11, 14, 17 and 19 years have a thirteenth month).

In the Bible (St. Luke, Chapter 22) we have a description of how Jesus ate the Passover with his disciples before going to Gethsemane. The Last Supper, the Agony in the Garden and the Crucifixion were at the time of the full moon following March 21st (Spring Equinox). The hurry to remove the body from the cross before the beginning of the Jewish Sabbath (Saturday) fixes the Crucifixion on a Friday.

The Church has sought to preserve this sequence. In 1961, T O'Beirne published in the journal New Scientist an algorithm called TEN DIVISIONS to EASTER for finding the Easter date for any year.

Algorithm to find the date of Easter for any year.

To use the the algorithm below, simply select the year you want to find the date of Easter for and then carry through the calculations as shown in the algorithm. Note that where the answer to a division is needed, you only want the whole number part, not any decimals. The remainder is what is left over after a division once the number as been split into as many whole parts as possible.

StepNumberDivide byAnswerRemainder
1x  =  year  =  100b = c =
25b + c19 - a =
33(b + 25)4r = s =
48(b + 11)25t = -
519a + r - t30-h =
6a + 11h319g = -
760(5-s) + c4j = k =
82j - k - h + g7-m =
9h - g + m + 11030n = q =
10q + 5 - n32-p =
Easter is the pth day of the nth month in the year x

 

Exercises

Work out the answers to the questions below and fill in the boxes. Click on the Click this button to see if you are correct button to find out whether you have answered correctly. If you are right then will appear and you should move on to the next question. If appears then your answer is wrong. Click on to clear your original answer and have another go. If you can't work out the right answer then click on Click on this button to see the correct answer to see the answer.

 

Question 1
Use the algorithm in the table above to calculate the date of Easter in the years below.
Write your answers in the form 10th April, not 10 April or 10/4. Use a capital letter for the first letter of the month.

(a)  2009
(b)  2010 
(c)  2011

 

Question 2
Use the Easter date generator below to find the date of Easter for the next 20 years (2009 to 2028). Record all the dates.

Year =  

Using the data you have collected from the generator, answer the questions below.
Enter dates in the same way as in Question 1.

(a)  What is the earliest date of Easter over the next 20 years?    
(b)  What is the latest date of Easter over the next 20 years?
(c)  How many times is Easter in March over the next 20 years?
(d)  How many times is Easter on 4th April over the next 20 years?


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Updated by R.D.Geach January 2008