On the first page of this section on calendars, which shows a perpetual calendar on which the day of the week might be found, I mentioned the Dominical Letter, which is used as one way of naming the day of the week on which a year starts. And, on a later page, in discussing the three cycles, the solar cycle of the Julian calendar, the Metonic cycle, and the cycle of the Indictions, which formed the basis for the Julian era on which Julian Day Numbers were based, I noted that the version of the Metonic cycle used was that which corresponded to the Golden Number.
Well, if I have discussed Dominical Letters and Golden Numbers, it seems reasonable that I should also discuss the calculation of the date of Easter, in which these things are used.
The table for the Dominical Letter is similar to that used for the perpetual calendar on the first page:
00 01 02 03 04 05
06 07 08 09 10 11
12 13 14 15 16
17 18 19 20 21 22
23 24 25 26 27
28 29 30 31 32 33
34 35 36 37 38 39
40 41 42 43 44
45 46 47 48 49 50
51 52 53 54 55
56 57 58 59 60 61
62 63 64 65 66 67
68 69 70 71 72
73 74 75 76 77 78
79 80 81 82 83
84 85 86 87 88 89
90 91 92 93 94 95
96 97 98 99
Gregorian
G F E D C B A 1600 2000 2400 2800 3200
B A G F E D C 1700 2100 2500 2900 3300
D C B A G F E 1800 2200 2600 3000 3400
F E D C B A G 1500 1900 2300 2700 3100 3500
Julian
F E D C B A G 400 1100
G F E D C B A 500 1200
A G F E D C B 600 1300
B A G F E D C 0 700 1400
C B A G F E D 100 800 1500
D C B A G F E 200 900 1600
E D C B A G F 300 1000 1700
In the case of a leap year, look under the space preceding the number for the year for the Dominical Letter applicable to the months of January and February. These letters apply to calendar years from January to December, rather than to a year beginning in March, as used for the perpetual calendar on the first page.
Easter, of course, falls on a Sunday.
March 21st of the Gregorian calendar is taken as the approximation to the vernal equinox to use.
The Metonic cycle of 19 years is corrected by a Lunar Equation and a Solar Equation to indicate the age of the Moon (given by the Epact) more accurately.
This table gives the Epact from the Golden Number and the displacement resulting from the Lunar and Solar equations:
Golden Number: 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19
Displacement:
1 1 12 23 4 15 26 7 18 29 10 21 2 13 24 5 16 27 8 19
0 * 11 22 3 14 25 6 17 28 9 20 1 12 23 4 15 26 7 18
-1 29 10 21 2 13 24 5 16 27 8 19 * 11 22 3 14 25 6 17
-2 28 9 20 1 12 23 4 15 26 7 18 29 10 21 2 13 24 5 16
-3 27 8 19 * 11 22 3 14 25 6 17 28 9 20 1 12 23 4 15
-4 26 7 18 29 10 21 2 13 24 5 16 27 8 19 * 11 22 3 14
and the changes in the displacement in years ending with two zeroes and the resulting displacement is shown in the table below:
Year Lunar Solar Displacement 1700 -1 0 1800 +1 -1 0 1900 -1 -1 2000 -1 2100 +1 -1 -1 2200 -1 -2 2300 -1 -3 2400 +1 -2 2500 -1 -3 2600 -1 -4 2700 +1 -1 -4 2800 -4
the shifts to the displacement repeating in the 1200 year cycle shown.
Based on the Dominical Letter, the Sundays following March 21st are:
March April A 26 2 9 16 23 B 27 3 10 17 C 28 4 11 18 D 22 29 5 12 19 E 23 30 6 13 20 F 24 31 7 14 21 G 25 1 8 15 22
and based on the Epact, the day on which the approximated Full Moon falls is:
Epact Date Epact Date Epact Date 22 March 22 12 April 1 2 April 11 21 March 23 11 April 2 1 April 12 20 March 24 10 April 3 * April 13 19 March 25 9 April 4 29 April 14 18 March 26 8 April 5 28 April 15 17 March 27 7 April 6 27 April 16 16 March 28 6 April 7 26,25 April 17 15 March 29 5 April 8 14 March 30 4 April 9 13 March 31 3 April 10
Epacts 26 or 25 give a Full Moon date of April 17 because the lunar month is about 29 and a half days long, not 30 days long, and so the year is taken as being composed of 30 day lunar months alternating with 29 day lunar months, and Easter is affected by that in this case.
Thus, starting with the date found from the Epact in the table above, in the row given by the year's Dominical Letter, look for the earliest date that agrees with it or is after it, and that will be the date of Easter.
As previously noted, the current cycle in which the Golden Number goes from 1 through 19 consists of the years from 1995 to 2013.
then you're probably using the wrong calendar.
Since this unlucky day is held to fall on a Friday, it is quite reasonable to suspect that this superstition has some connection with Good Friday, on which the Crucifixion is commemorated.
The number 13 may be considered unlucky as a number for a number of reasons.
When one considers those odd, strange, and peculiar numbers known as prime numbers, one might think of them this way:
Or, it is also held that, given Jesus and the 12 Apostles, Judas was the 13th person at the table at the Last Supper.
However, there is another association between the number 13 and the Crucifixion which is more definitely calendrical in nature.
Before the Gregorian calendar was adopted, the calculation of Easter for the Julian calendar was accomplished in a manner similar to the one above, but somewhat simpler.
But this practice was one instituted by the Roman Church. The preceding practice of the early Christian church was to celebrate Easter on Nisan 14th each year, regardless of the day of the week on which it fell. Since the Jewish months begin on the New Moon, the 14th of the month would be a representation of the Full Moon.
And, when Nisan 14th, Passover, falls on the Sabbath, and by this I mean Saturday, the Jewish Sabbath, not Sunday, the Day of the Lord as followed in Christian worship, as it is recorded by the Gospels as having taken place subsequent to the Crucifixion, then Nisan 13th would be a Friday.
However, if this is the case, it is based on a popular misconception. The Biblical account of the Crucifixion notes that the Last Supper took place on Passover. Christ was arrested the day after that, and handed over to Pontius Pilate one day later. This was the day of the Crucifixion, and the Bible also notes that Christ lay dead for three days and three nights. And then it notes that Christ was found to be risen early on Sunday morning.
This would seem to mean that Christ appeared before Pontius Pilate on Wednesday, so that while He was placed on the Cross on Wednesday, His death took place at some time on the night between Wednesday and Thursday, and then, three days later, His resurrection took place on the night between Saturday and Sunday. In that case, the arrest of Jesus took place on Tuesday, and Passover was on Monday.
This is not entirely certain; the arrest of Jesus could have taken place in the evening following Passover, on what we would regard as the same day. And many Christian denominations take the position that the statement concerning Christ being in the grave for three days and three nights is not to be taken literally.
Thus, the Crucifixion may have taken place on Wednesday or Thursday, and Passover of that year, the day of the Last Supper, would have been either Monday, Tuesday, or Wednesday.