Easter a movable feast Easter is a moveable feast
: its date varies from year to year because it is correlated with the lunar cycle. The
Passover and Easter Christian
follow different rules of calculation and therefore are almost never in the same date. Within Christianity, then there are two different rules depending on whether you use the Gregorian calendar (Catholic and Protestant), or the Julian (Orthodox). These two rules in a few years give the same date (and therefore all Christians celebrate Easter on the same day), different dates in other years.
2010
Christian Easter (Gregorian calendar): April 4
Passover : March 30
Easter to the Julian calendar: March 22
The First Council of Nicaea (325 years) established that the solemnity of Easter would be celebrated in Sunday following the first full moon (the fourteenth day of the ecclesiastical moon) that is after the spring equinox .
Over the centuries V-VII the method is said to complete tables of dates of Easter, based on the cycle of diciannovennale Methone, the fifth century BC Athenian astronomer
In practice, the date of Easter was the result an algorithm that combined cycle Methone, and therefore the number of gold , with the solar cycle, resulting in a cycle 19 x 28 = 532 years. Let's see how.
The number of gold
The rotation of the Moon is in a period of time equal to that of its revolution around the Earth, specifically in 27 days, 7 hours and 43 minutes. This period is called the sidereal month . However, as the Earth moves along its orbit around the Sun while the Moon completes its movement around our planet, it follows that the Moon does not return in conjunction with the Sun after a sidereal month, but with a lag . We speak therefore of the lunar month that is 29 days, 12 hours, 44 minutes and 3 seconds.
sidereal month: 27 days, 7 hours and 43 minutes
lunar month: 29 days, 12 hours, 44 minutes and 3 seconds
Methone discovered that 235 lunar months are almost exactly 19 solar years:
(29.5 x235): 369 = 18.99
For this reason, after a 19-year cycle (called Methone cycle) phases of the Moon return to the same day of the year.
In other words, after observing the days when they had which the different phases of the moon for 19 years, you will notice that the twentieth year they fall on the same days of the first year, the twenty-first year will fall on the same days of the second year, and so on.
is why the number of times, starting from the year 1 BC, was divided into periods of 19 years, and each year of each period was combined with a natural number from 1 to 19. The number of gold is thus the number of the year in the lunar cycle in progress. To find
then the number of gold relating to any year can be obtained by dividing the year to 19 and increasing by one the rest obtained.
EXAMPLES -To the year 1990, for example, the calculation is: 1990: 19 = 104 with the rest of 14, 14 + 1 = 15;
that the golden number for 1990 is 15 .
In 2010, 2010:19 = 105 is the rest 15, from which 15 +1 = 16
The golden number is an index of cyclicity: the same number is repeated every 19 years.
If the lunar month lasts 29.9 days, the lunar year lasts 354 days, compared with 365 in the calendar year (366 in leap years). L ' epact (from greek: epaktai hemèrai = added days) is the number of days in which the common solar year of 365 days exceeds the common lunar year of 354 giorni (29,5x12=354).
L'epatta è definita come l' età della Luna al 1 gennaio , vale a dire il numero di giorni trascorsi dall'ultima Luna nuova; questo numero può andare da 1 a 30. Per esempio, nel 2010 la luna nuova di gennaio è stata il 15. Dal calcolo 29-15=14 risalgo all’età della luna il primo gennaio. L’epatta è 14.
Un anno (solare) ha generalmente 365 giorni (366 negli anni bisestili). Un anno lunare ha ha 12 × 29,5 = 354 giorni. Pertanto l'anno solare dura 11 giorni in più dell'anno lunare.
Suppose a solar year and lunar year start on the same day. At the beginning of the next calendar year, have already passed 11 days of the Lunar New Year (ie, are phase shifted 11 days). After two years the difference has accumulated to 22 days: the beginning of the lunar month occurs 11 days earlier each year. These days in excess of the calendar year compared to the lunar year are called epacts. You must add a day in the calendar to know the day of the lunar year.
EXCEPTIONS IN CORRESPONDENCE OF 24 AND 25 epact
Since dell'epatta 30 possible values \u200b\u200b(0 to 29), should result in 30 different dates per il giorno del termine pasquale.
Tuttavia la Chiesa ha stabilito ormai da moltissimi secoli che la data di Pasqua debba cadere tra il 22 marzo e il 25 aprile, ossia che il termine pasquale possa verificarsi fra il 21 marzo e il 18 aprile, poiché in realtà il 19 aprile potrebbe già essere la data del plenilunio successivo al primo di primavera. I giorni possibili per il termine pasquale si riducono così a 29.
Per questo motivo tutti i metodi di calcolo della data di Pasqua prevedono due eccezioni : la prima per evitare che la data di Pasqua possa risultare il 26 aprile (in questo caso la correzione avviene nel senso di anticiparla alla domenica precedente, ossia il 19 April ) and the other, so that in the same cycle of Methone diciannovennale occur two terms Easter (Paschal full moon) with the same date (this because it is inconsistent with the logic of the cycle of Methone).
The following rule is used to calculate the epact a any Gregorian year (in brackets the calculation for 2010):
multiplies the number of gold for 11 (16x11 = 176) , you subtract 10 from the product (166), the result is divided by 30, and you get a rest (5 rest 16), denoted with a (16). Si sottrae 15 dal numero secolare dell'anno proposto (20-16=4) e si ha un numero b (4). Si divide b per 25 (4:25=0,16), si toglie il quoziente dal dividendo (4-0=4), si divide questa differenza per 3 (4:3=1 resto 1), e si ottiene un quoziente c (1). Si moltiplica b per 3 (4 x3=12) , si divide il prodotto per 4 ( 12:4=3 resto3), e si ottiene un quoziente d (3). Si sottrae c da d ( 3-1=2 ), e si divide il risultato per 30 ( 2:30= 0 resto 2); il resto di questa divisione sia chiamato e (2). Se infine si sottrae e da a ( 16-2=14) , One gets the epact. In the event that it is more of a, is subtracted from and to then subtract the result from 30, resulting in the epact. Of all the ratios is considered only the integer part, ignoring the decimal digits.
The scheme of operations to be performed is the following:
[(No gold x 11) - 10]: 30
(r) = rest = a;
No years old - 15 = b;
[b - (b: 25)]: 3 = c;
(b x 3) : 4 = d;
(d - c) : 30
(r) = resto = e;
a - e = epatta;
oppure:
30 - (e - a) = epatta.
Per il 2010 abbiamo trovato 14.