Working Out the Date of Easter Day

Because the Church calendar follows the moon, Easter Day can be on any Sunday from March 22nd to April 25th!
Easter is the Christian celebration of the anniversary of the Death and Resurrection of Jesus Christ. This happened on a date representing the first Full Moon of Spring on the Jewish Calendar. Because of that, Easter Day is always the first Sunday after the first calculated Full Moon on or after March 21st. If the Full Moon is on a Sunday, Easter Day is on the next Sunday.

For the past 1500 years, March 21st has been used to represent the date of the March equinox (the real equinox might be a day or two different). There are two equinoxes a year, one in March and one in September. Equinox means 'equal night' and on the Equinoxes the day and night are of the same length. The March Equinox is also known as the Vernal Equinox.

Several methods have been used since early Christian times to work out the date of Easter Day. It was made more complicated in 1582 when Pope Gregory XIII replaced the old Roman 'Julian' calendar (started by Julius Caesar) with a new more accurate 'Gregorian' calendar, which most people still use today. In the UK, Easter was first calculated using the Gregorian calendar in 1753 when the country had changed calendars.
Catholic and western Christians now use the Gregorian calendar to find the date of Easter. However, some Orthodox churches celebrate Easter Day on a different day because they still use the old Julian Calendar (which is now 13 days behind the Gregorian calendar) and also a different moon to calculate from.
In the Gregorian Calendar, Easter can be on the dates from March 22nd to April 25th.

In 2008, Easter was on March 23rd, about as early as it can be. This is probably the earliest Easter anyone reading this page will see in the rest of their lives! You'll have only had an earlier Easter if you're over 95 years old (it happened in 1913)! And no one has ever, or will, see it any earlier!
The next time Easter will be as early as in 2008 will be in the year 2160!
The next time it will be on March 22nd (as early as it can be), will be in the year 2285. Easter last occurred on March 22nd in 1818! (However, in Orthodox churches in 2010 Easter will be on March 22nd. It will be on April 4th in the Gregorian calendar.)

Working out the date of Easter Day is extremely tricky and you need to be pretty good at Maths to do it! There are still several version of how to calculate the date. Below is a version with all the complicated maths already done (it works for the Gregorian calendar for the years 1900 to 2199), so all you have to do is:

1. Divide the year number by 19:
   2009/19=105.73
2. Multiple the number before the decimal point by 19 (105 for 2009):
   105x19=1995
3. Then subtract the result from Step 2 from the year number:
   2009-1995=14
4. Add 1: 14+1=15
5. Look up the 'Golden Number' in the following table (15 for 2009!).
   Easter is on the first Sunday after the date in the table.
   In 2009 Easter is on April 12th, so it works!

Golden Number	Date	Golden Number	Date	Golden Number	Date
0	March 27	7	April 8	14	March 22
1	April 14	8	March 28	15	April 10
2	April 3	9	April 16	16	March 30
3	March 23	10	April 5	17	April 17
4	April 11	11	March 25	18	April 7
5	March 31	12	April 13	19	March 27
6	April 18	13	April 2

The number 19 is used to find the 'Golden Number' because the dates of Full Moons repeat, almost exactly, every 19 years. The dates in the table are the dates of the 'Paschal Full Moon' (a 'representative' Full Moon used in the calculations!), which represents the real Full Moon quite closely.
If you'd like to know more about working out the date of Easter and things like Equninoxes, here are a some sites: