Good morning, HappyEaster, and welcome to the earliest Easter Sunday that you will ever experience. And here, very simply, is why it's so early. Easter is the first Sunday after the first full moon after the spring equinox. This year, 2008, everything in this list has happened really really fast...
Equinox: Friday 21st March Full Moon: Saturday 22nd March Easter Sunday: Sunday 23rd March
Bang, bang, bang. You can't beat that.
Golden
Number
Day of
Month
Sunday
Letter
March 21
C
XIV
March 22
D
III
March 23
E
March 24
F
XI
March 25
G
March 26
A
XIX
March 27
B
VIII
March 28
C
March 29
D
XVI
March 30
E
V
March 31
F
April 1
G
XIII
April 2
A
II
April 3
B
April 4
C
X
April 5
D
April 6
E
XVIII
April 7
F
VII
April 8
G
April 9
A
XV
April 10
B
IV
April 11
C
April 12
D
XII
April 13
E
I
April 14
F
April 15
G
IX
April 16
A
XVII
April 17
B
VI
April 18
C
April 19
D
April 20
E
April 21
F
April 22
G
April 23
A
April 24
B
April 25
C
As I mentioned on Friday, we have a full moon on 22nd March once every 19 years. It's a common event. The reason that 2008 is so special is that 22nd March is a Saturday, allowing 23rd March to be a Sunday. There are seven possible days of the week on which the 23rd can fall, and only when it's a Sunday does the ultimate Easter occur. A one in 19 chance, multiplied by a 1 in 7 chance, that's an event of 1 in 133 year rarity.
OK, so once you know the date of the first spring full moon in any year, how do you find the date of the next Sunday? Ah, well, that's where the Sunday Letter comes in. Know the Sunday Letter and you can work out which of the next seven days is a Sunday. Every year is assigned its own Sunday Letter (one of the letters from A to G), roughly corresponding to the seven different days of the week on which January 1st can fall. This Easter the Sunday Letter is E. Next year it's D, then C, then B, and then for 2012 (a leap year) it skips A and flips back round to G. There's a ready-made list of Sunday Letters for the 20th and 21st centuries here.
You can then use today's big long table, reproduced from the Book of Common Prayer, to work out the date of Easter. For any particular year you need to know only two things - the Golden Number (see Friday's post) and the Sunday Letter. Start in the first column with the Golden Number. Then move down the table until you find the next row with the correct Sunday Letter. That's the date of Easter Sunday. Simple?
• For example, in 2008 the Golden Number is 14 (XIV), so start on the March 22nd row. The Sunday letter is E so move down to the next E, which is March 23rd. And so Easter is March 23rd.
• For example, last year the Golden Number was 13 (XIII), so start on the April 2nd row. The Sunday letter was G so move down to the next G, which is April 8th. And so Easter was April 8th.
• Oh, and if the full moon is on a Sunday, then Easter jumps to the following Sunday. That's to make sure it's never celebrated on the same day as the Jewish Passover.
Whichever date is associated with the Golden Number, Easter can fall on any of the seven dates below it. So not every year with a Golden Number of 14 has a really early Easter. In 2027, for example, Easter will fall on March 28th (Sunday Letter C) and in 1970 Easter was as late as March 29th (Sunday Letter D). Easter 2008 is only fabulously early because the Golden Number is 14 and the Sunday Letter is E.
Meanwhile down at the bottom of the table, Easter can sometimes run very late. This tends to happen when the Golden Number is 6 (as in 2000), 9 (as in 2003) or 17 (as in 2011). The latest Easter of all (April 25th) can only happen in a year with Golden Number 6 and Sunday Letter C - years such as 1943 and 2038. But we've got a close contender coming up very soon. In 2011 everything in the Easter calculation list is going to run really really slowly...
Equinox: Monday 21st March Full Moon: Sunday 17th April Easter Sunday: Sunday 24th April
So, calendar freaks, do come back in three years time. In 2011 we've got an extremely late Easter on our hands. And you just wouldn't believe how rare it is to have an extreme late Easter so close to an extreme early Easter...
• The cycle of Easter dates repeats every 5,700,000years. During this period, Easter falls on March 23rd only 54,150 times (less than 1% of the total).
• Today, March 22nd, is the least likely date for Easter to fall - this happens in less than ½% of years. April 19th is the most likely, at nearly 4%.
• Easter falls on March 28th in both 2027 and 2032, a gap of five years. No shorter interval is possible.
• Almost exactly half of our Easters occur on the same date 11 years later (but never more than four in a row). For example, Easter falls on March 31st in 1991, 2002, 2013 and 2024, but not in 2035.
• Consecutive Easters are always separated by 350, 357, 378, or 385 days (that's 50, 51, 54, or 55 weeks). For example, Easter 2008 is 350 days after Easter 2007, but 385 days before Easter 2009. So we've just had the shortest possible gap between Easters, and we're about to enter the longest.
• In 1926 the League of Nations proposed that Easter Sunday be observed on the first Sunday after the second Saturday of April (i.e. the Sunday nearest April 12th). However world religions failed to agree on this simplification, and so the movable lunar feast continues.
• The last time Easter fell before the clocks went forward was in 1959 (back when the clocks changed to British Summer Time in mid-April, not March).
• The coldest recent UK Easter was in 1964. Over the weekend 27-29 March temperatures barely reached 6°C in southern and central parts of the country, and were accompanied by a raw easterly wind.
• The snowiest recent UK Easter was in 1983. Over the weekend 1-3 April there was up to 10cm of snowfall in Scotland, the Midlands and Kent. The following Easters were all snowy: 1958, 1965, 1970, 1973, 1975, 1977, 1978, 1982, 1983, 1986, 1994 and 1998.
Here's a table showing the date of Easter from 1900-2099
If there's a digit in the table then Easter is in March, and that's the last digit of the date (22nd-31st).
If there's a letter in the table then Easter is in April, and the letter follows the code a=1, b=2, c=3 etc.
» For example, the symbol in the table for 2008 is a digit, so Easter is in March. That digit is a 3, so Easter is on March 23rd. » For example, the symbol in the table for 2009 is a letter, so Easter is in April. That letter is L, which is the 12th letter of the alphabet, so Easter is on April 12th.
Here's a list of really earlyEasters, so you can see how rare they really are:
• Easter on 22nd March: last happened 1818, next happens 2285
• Easter on 23rd March: last happened 1913, next happens 2160
• Easter on 24th March: last happened 1940, next happens 2391
• Easter on 25th March: last happened 1951, next happens 2035
• Easter on 26th March: last happened 1989, next happens 2062
• Easter on 27th March: last happened 2005, next happens 2016 (but then not again until 2157)
Extreme
Early
Easter (full moon 18:50 GMT, 21/03/07)
The Easter story, according to the Bible, is intrinsically linked to the Jewish festival of Passover. And Passover is a lunar festival, linked to the date of the full moon. So Easter has to be linked to the date of the full moon too. Here's how the date of Easter is determined...
Easter Day is the first Sunday after the first full moon after the spring equinox.
To get an early Easter you need an early full moon. Like we have this year. This year the spring equinox was yesterday, the next full moon is today, and so Easter is on Sunday. It's not very often that there's a full moon almost immediately after the equinox and then a Sunday very soon afterwards. And that's why Easter is bloody early this year. Happy with that? Good, please stop reading now.
OK, now for the real, rather more complicated explanation. You knew it wouldn't be that simple, didn't you? One reason for this is because the church's method of determining Easter doesn't use the real spring equinox, it always uses March 21st. You can thank the Council of Nicæa in 325AD for that one. And Easter calculations don't use the date of the real full moon either, they use something called the Paschal Full Moon instead. These form an artificial list of full moon dates, applicable globally, almost but not quite linked to the real ones. So the actual rule for determining the date of Easter is this...
Easter Day is the first Sunday after the Paschal Full Moon on or after March 21st.
Let's take a more detailed look at these mysterious Paschal Full Moons. The ancient church didn't want to have to mess around with actual astronomical data, because that was quite difficult to predict accurately in those days, and leap years kept getting in the way. So they took advantage of a convenient lunar coincidence called the Metonic Cycle and used this to help. The phases of the Moon may not repeat on the same day every year, but they do repeat (give or take 2 hours) on the same day every 19 years. So if you know the dates of the spring full moons over a 19 year period, you can repeat that list every 19 years afterwards. Simple?
Table to find the date of
the Easter Full Moon
Golden
Number
Years
Full Moon
I
1976 1995 2014
April 14
II
1977 1996 2015
April 3
III
1978 1997 2016
March 23
IV
1979 1998 2017
April 11
V
1980 1999 2018
March 31
VI
1981 2000 2019
April 18
VII
1982 2001 2020
April 8
VIII
1983 2002 2021
March 28
IX
1984 2003 2022
April 16
X
1985 2004 2023
April 5
XI
1986 2005 2024
March 25
XII
1987 2006 2025
April 13
XIII
1988 2007 2026
April 2
XIV
1989 2008 2027
March 22
XV
1990 2009 2028
April 10
XVI
1991 2010 2029
March 30
XVII
1992 2011 2030
April 17
XVIII
1993 2012 2031
April 7
XIX
1994 2013 2032
March 27
Here's a table showing the 19 possible Paschal Full Moons. I've listed all the years from 1976 to 2032, but you can trawl back as far as 1900 and forward as far as 2199 should you want to. Remember, these are all artificial full moons for calculation purposes only.
Every year on the same line has the same full moon date. For example, the Paschal Full Moon in 1995 fell on April 14th, the same as 19 years earlier in 1976 and 19 years later in 2014. These years are described as having a Golden Number of 1 (which is the remainder when dividing the year by 19, plus 1). Don't worry about that. All you need to know is that every year with the same Golden Number has the same Paschal Full Moon. Every year with a Golden Number of 1 (including 1900 and 2185, for what it's worth) has its post-equinox full moon on April 14th.
Scanning down the table you'll see that the first post-equinox full moon in the year 2000 was on April 18th, and that's the latest date possible. It's years with a Golden Number of 6 that have the very latest Easters. And the Paschal full moon this year is on March 22nd, which is the earliest date possible. It's years with a Golden Number of 14 that have the very earliest Easters. Well, near enough, but I'll come back to the extra complications on Sunday.
And one more thing. During the 20th, 21st and 22nd centuries the Paschal Full Moon never falls on March 21st itself, which means that Easter Day can never fall as early as March 22nd. But in other centuries the table of Paschal Full Moons is different. Throughout the 19th century, for example, March 21st was linked to a Golden Number of 14 (that's because 1900 wasn't a leap year, so the pattern skipped a day). And hey presto, in 1818 there actually was an Easter Day on March 22nd. Similarly there'll be another March 22nd Easter in the 23rd century, in 2285. But between 1900 and 2199, March 23rd is the earliest Easter we can possibly get. It really is an utterly extreme Easter this year. Sorry, is anybody still reading? I did warn you to stop earlier, didn't I?
Extreme
Early
Easter (vernal equinox 05:48 GMT, 20/03/07)
It can't have escaped your notice that there's an early Easter this year. Like, very very early. March 23rd is a ridiculously early date for Easter to fall, but that's the way the calendar works out this year. Oh yes, this is most definitely an Extreme Early Easter.
This year's Easter isn't quite record-breakingly early, but it nearly is. There's not been an Easter this early since 1913, which is nearly a century ago and you won't remember that. There won't be an Easter this early again until 2160, which is more than a century and half away and you definitely won't be around for that. And there won't be an earlier Easter than this until 2285, which is so far into the future that we'll probably have drowned the planet by then. Oh yes, this is most definitely an Extreme Early Easter.
Thanks to to some verycomplicatedecclesiasticalrules involving equinoxes and full moons (which I'll go into tomorrow), Easter Day can fall on any Sunday between March 22nd and April 25th. The period between March 28th and April 20th is the most common, and any Easters outside that range are rather less frequent. This year we're right up at the start of the possible range, on March 23rd, because a couple of unlikely events have combined to create a freak rarity. An Extreme Early Easter.
As a movable feast, Easter feels very wrong when it moves too early. It may be nearly three months since we last had a bank holiday, but somehow mid-March is too early to be having a double bank holiday break. School holidays are also all over the place this year because of the early Easter. Some schools are breaking up today and having the next couple of weeks off, whereas others are waiting until mid-April, when Easter "normally" is, and having their break then. Hell, we've not even put the clocks forward yet. And look at the weather, it's more like winter than spring out there. Actually, maybe there's a reason for that. An Extreme Early Equinox.
Today is the first day of spring* - the vernal equinox. The overhead Sun crossed the equator at 05:48 this morning, and we're now entering into the warm half of the year. Yes really, March 20th, not March 21st, is the first day of spring. Spring used to start on March 21st, certainly a century ago it did, but the shifting equinox means that it'll now always be on March 20th. Well, every year from 2008 until 2044 anyway. I explained all this last year, were you not paying attention?
* yes yes yes, I know, northern hemisphere only
It takes the Earth approximately 365 days, 5 hours and 49 minutes to orbit the Sun, so every year the spring equinox shifts almost 6 hours later than the year before. That's approximately 24 hours later every 4 years, which is then cancelled out by the presence of a February 29th a few weeks before the next spring equinox occurs. But this still leaves the calendar 11 minutes short of reality every year, and this tiny difference shifts the spring equinox approximately three-quarters of an hour earlier every 4 years.
So it's not just Easter that's early this year, it's spring too. An equinox before sunrise on March 20th - it's unheard of. In fact the spring equinox hasn't taken place before 6am on March 20th since 1896. Spring hasn't begun this early since the 19th century! But don't get too excited. The phrase "spring hasn't begun this early since the 19th century" has been true every leap year since 1900, and will continue to be true every leap year until 2024. So our premature spring isn't the reason why Easter is early this year. Our early Easter is a result of something that's happening tomorrow. Come back then and I'll tell you more.
Extreme
