Easter Sunday Calculation

Easter Sunday

Easy and hard ways to calculate Easter Sunday's date.

• Date Calculation
• Easter Date Trivia
• Easter Bonnets and Easter Parades
• Funny Easter Eggs

When is Easter Day?  Dates for Easter Sunday

• 2010 April 4th
• 2011 April 24th

Easter Sunday Calculation

Easter Sunday celebrates the day when Jesus Christ was resurrected.  On Good Friday, Christ was crucified and then buried.  But on the third day, he rose from the dead.  Thus Easter Sunday is the most important date in the Christian calendar, far more important than even Christmas day - Jesus' birth.

Fewer than one person in a thousand could tell you how the date for Easter Sunday is determined and thus explain precisely why Easter falls on a different date each year.  While many people will tell you the moon was a factor, few realize that the vernal equinox plays a crucial role in the calculation.

This simplistic calculation for 'When is Easter' works for most years:

1) Start your calculation from the Vernal Equinox, which is usually on March 21st.

2) Consult a diary to determine the next full moon.  Easter falls on the following Sunday.

See the full complex calculation for when Easter falls.

Easter Date Trivia

As mentioned earlier, Easter Sunday is set by the 1st full moon after the Spring Equinox (which is March 20).  Here's the interesting info. This year 2008 is the earliest Easter any of us will ever see the rest of our lives! And only the most elderly of our population have ever seen it this early (95 years old or above!). And none of us have ever, or will ever, see it a day earlier! Here's the facts:

1) The next time Easter will be as early as March 23 will be the year 2228 (200+ years from now). The last time it was this early was 1913 (so if you're 95 or older, you are the only ones that were around for that!).

2) The next time it will be a day earlier, March 22, will be in the year 2285 (275+ years from now). The last time it was on March 22 was 1818. So, no one alive today has or will ever see it any earlier than this year!

Days derived from Easter

Palm Sunday is always on the Sunday before Easter

Mothering Sunday (UK) 3 weeks before Easter

Ash Wednesday, which marks the start of lent is 46 days before Easter.  The calculation of 40 days for lent discounts Sundays, thus explaining the discrepancy between 46 and 40.  There is also 'Shrove Tuesday' otherwise known as 'Pancake Day'.

Easter Bonnets and Easter Parades

In times gone by, Easter bonnets [spring bonnets] were commonplace.  People liked to dress up in their finest clothes for the festival.  Women would consider it a matter of pride to buy a new bonnet for Easter, the frillier and more luxurious the better.

This appears to be in many ways a reaction to the ending of the Christian period of Lent.  During Lent, many Christians deny themselves luxuries.  So when Lent ended, going out and buying an Easter bonnet was an enjoyable way to greet Easter.  Spring time in general represents an end of the deprivations and restrictions of winter.

Easter bonnets were also worn in the Easter parades that used to be more common than they are today.

The heyday of bonnet wearing in the US was probably the 1930s. In his song "Easter Parade," Irving Berlin includes the following lines:

'In your Easter bonnet, with all the frills upon it,
You'll be the grandest lady in the Easter Parade.
I'll be all in clover and when they look you over,
I'll be the proudest fellow in the Easter Parade.
On the avenue, Fifth Avenue, the photographers will snap us,
And you'll find that you're in the rotogravure*.
Oh, I could write a sonnet about your Easter bonnet,
And of the girl I'm taking to the Easter Parade.'

The song also went on to be featured in the 1948 movie "Easter Parade". In recent years the custom of wearing Easter bonnets has rather declined.

* A printing process in which letters and pictures are transferred from an etched copper cylinder to a web of paper, plastic, or similar material in a rotary press. Printed material, such as a newspaper section, produced by this process

The Full, Complex Calculation for 'When is Easter'

Fortunately these extra nuances only come into play every 20 years or so.

For 2000 years it is the Church that calculates when Easter falls.  They are the sole arbiters of this date. Their calculations fix the Vernal Equinox at March 21st, even if astronomically, it falls on March 20th.  Moreover, the ecclesiastical full moon is always 14 days from the ecclesiastical new moon.  This may vary by one day from the astronomical full moon.

There are two more variables.  The international date line may potentially cause the full moon to fall on different days in different parts of the world.  Finally some Eastern Churches use the Julian calendar instead of the more modern Julian calendar, this factor produces the biggest practical difference in the determination of Easter.

Formula to Calculate Easter

This formula calculates the date of Easter Sunday.  The algorithm uses the y for year, m for month and d for the day of Easter.  Note * means multiply and when you divide, discard any remainder, thus 11 / 5 = integer 2

c = y / 100
n = y - 19 * ( y / 19 )
k = ( c - 17 ) / 25
i = c - c / 4 - ( c - k ) / 3 + 19 * n + 15
i = i - 30 * ( i / 30 )
i = i - ( i / 28 ) * ( 1 - ( i / 28 ) * ( 29 / ( i + 1 ) ) * ( ( 21 - n ) / 11 ) )
j = y + y / 4 + i + 2 - c + c / 4
j = j - 7 * ( j / 7 )
l = i - j
m = 3 + ( l + 40 ) / 44
d = l + 28 - 31 * ( m / 4 )

For example, using the year 2009
y = 2009
c = 2009/100 = 20
n = (2009 - ((19  * (2009/19)) = 14
k = 79
i = 2009 - (2009/4 - (2009-79) /3 + 19 * 14 + 15

....

m = 4

d = 12

See more funny Easter bunny pictures and rabbit jokes

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