Part 10 (1/2)
After having found the paschal full moons for one lunar cycle, a period of nineteen years, then the paschal moons again occur in the same order, on the same days of the month, as they did nineteen years before. Now, as has also been shown in the preceding chapter, this cycle might have been continued indefinitely had the Julian intercalation been followed without correction, and the cycle been perfectly exact; but neither of these being true, two equations or corrections must be made, one depending on the error of the Julian calendar, which is called the solar-equation; the other on the error of the lunar cycle, which is called the lunar equation.
Every omission of the intercalary day, which occurs three times in 400 years, will cause the full moons to fall one day later; for example, on the 13th of the month instead of the 12th. On the other hand, as has also been shown in the preceding chapter, the error of the lunar cycle is one day in 300 years; so that at the end of every 300 years the full moons will fall one day earlier, for example, on the 11th of the month instead of the 12th. Now, when both equations occur together, they compensate each other; that is, while the solar equation would cause the full moon to fall on the 13th, the lunar equation would make it fall on the 11th; therefore, no correction is to be made--there is nothing to correct. Had they occurred singly, the full moon, at the beginning of the cycle, would have fallen either on the 13th or the 11th; but as they occur together, no change is made; and the full moons of the calendar will remain as they are for the next one hundred years.
Hence, the date of Easter may very easily be determined, as indicated in the following tables (q. v.). It is known by actual calculation that the paschal full moon fell on the 12th of April in the year 1596, which moon was the first of a cycle after the reformation of the calendar by Gregory.
Now, by taking the epact of the following years of the cycle, which are 11, 22, 3, 14, 25, etc., from 12, the date of the first paschal moon, and you will have all the moons of the cycle. Of course, the epacts 22, 25, etc., cannot be taken from 12, but being carried back from the 12th of April, they will show on what day in March the full moons fall. When the epacts are greater than 12, it would be more convenient to take them from 43, as the number of days in March being 31, so 12 + 31 = 43.
To find the paschal moons of the cycle, we have then this rule: If the epact is less than 12, take it from 12; if greater, take it from 43, and the remainder will be the date of the paschal moon; unless the full moon fall before the 21st of March, in which case the following moon will be the paschal moon, which happens thirty days later. But when the solar equation occurs in 1710, causing the cycle to commence with the 13th of April, then the epacts must be taken from 13, or 13 + 31 = 44. And again in 1900, the correction makes the cycle commence on the 14th of April; so the number from which the epacts are taken is 14, or 14 + 31 = 45, and so on. Whenever there is a change of date of the paschal moon in the beginning of the cycle, as there is again in 2204, 2318 and 2413, etc., as may be seen in the following tables, then the epacts must be taken from that date, or that date plus 31, the number of days in March.
Or the date of the paschal moons may very easily be determined by taking eleven successively from the date of every preceding full moon, and that will give the date of the paschal moons; only it should be borne in mind that, whenever the full moon falls before the 21st of March, the following moon is the paschal moon, which happens thirty days later.
As Easter Sunday is the first Sunday after the paschal full moon, so all that remains to be done in fixing the date of Easter, is to find the day of the month on which that Sunday falls; and as this can easily be done by the use of the dominical letter, which letter and its use in fixing dates having been fully explained in Part Second, Chapters IV and V, (q. v.), a repet.i.tion seems to be unnecessary here.
-----------+-------+----------+---------+--------+--------- _Dominical_
_Year._
_Paschal_
_Easter._
_Epact._
_Golden_ _Letter._
_Full_
_Number._
_Moon._
-----------+-------+----------+---------+--------+--------- gf
1596
April 12
14
0
1 e
1597
” 1
6
11
2 d
1598
March 21
22
22
3 c
1599
April 9
11
3
4 ba
1600
March 29
2
14
5 g
1601
April 17
22
25
6 f
1602
” 6
7
6
7 e
1603
March 26
30
17
8 dc
1604
April 14
18
28
9 b
1605
” 3
10
9
10 a
1606
March 23
26
20
11 g
1607
April 11
15
1
12 fe
1608
March 31
6
12
13 d
1609
April 19
26
23
14 c
1610
” 8
11
4
15 b
1611
March 28
3
15
16 ag
1612
April 16
22
26
17 f
1613
” 5
7
7
18 e
1614
March 25
30
18
19 d
1615
April 12
19
0
1 cb
1616
” 1
3
11
2 a
1617
March 21
26
22
3 g
1618
April 9
15
3
4 f
1619
March 29
31
14
5 ed
1620
April 17
19
25
6 c
1621
” 6
11
6
7 b
1622
March 26
27
17
8 a
1623
April 14
16
28
9 gf
1624
” 3
7
9
10 e
1625
March 23
30
20
11 d
1626
April 11
12
1
12 c
1627
March 31
4
12
13 ba
1628
April 19
23
23
14 g
1629
” 8
15
4
15 f
1630
March 28
31
15
16 e
1631
April 16
20
26
17 dc
1632
” 5
11
7
18 b
1633
March 25
27
18
19 -----------+-------+----------+---------+--------+---------
By close examination of the above tables, it will be seen that there is just eleven days difference in the date of these paschal moons, from year to year, through the whole lunar cycle, and through all lunar cycles. In determining the date of Easter, it will also be seen, that whenever the full moon falls before the 21st of March, then the following moon, which happens thirty days later, is the paschal moon, as the 21st of March is its earliest possible date. Also when the cycle is
-----------+-------+----------+---------+--------+--------- _Dominical_
_Year._
_Paschal_
_Easter._
_Epact._
_Golden_ _Letter._
_Full_
_Number._
_Moon._
-----------+-------+----------+---------+--------+--------- a
1634
April 12
16
0
1 g
1635
” 1
8
11
2 fe
1636
March 21
23
22
3 d
1637
April 9
12
3
4 c
1638
March 29
4
14
5 b
1639
April 17
24
25
6 ag
1640
” 6
8
6
7 f
1641
March 26
31
17
8 e
1642
April 24
20
28
9 d
1643
” 3
5
9
10 cb
1644
March 23
27
20
11 a
1645
April 11
16
1
12 g
1646
March 31
1
12
13 f
1647
April 19
21
23
14 ed
1648
” 8
12
4
15 c
1649
March 28
4
15
16 b
1650
April 16
17
26
17 a
1651
” 5
9
7
18 gf
1652
March 25
31
18
19 e
1653
April 12
13
0
1 d
1654
” 1
5
11
2 c
1655
March 21
28
22
3 ba
1656
April 9
16
3
4 g
1657
March 29
1
14
5 f
1658
April 17
21
25
6 e
1659
” 6
13
6
7 dc
1660
March 26
28
17
8 b
1661
April 14
17
28
9 a
1662
” 3
9
9
10 g
1663
March 23
25
20
11 fe
1664
April 11
13
1
12 d
1665
March 31
5
12
13 c
1666
April 19
25
23
14 b
1667
” 8
10
4
15 ag
1668
March 28
1
15
16 f
1669
April 16
21
26
17 e
1670
” 5
6
7
18 d
1671
March 25
29
18
19 -----------+-------+----------+---------+--------+---------
completed, then the paschal moons again occur in the same order, on the same day of the month as they did nineteen years before. Now this cycle is six times repeated in a period of 114 years, when the intercalary day being suppressed in 1700, causes the first paschal moon of the cycle to fall on the 13th of April instead of the 12th, and all the moons of the cycle to fall one day later than they would had the correction not been made. The cycle is now repeated ten times without
-----------+-------+----------+---------+--------+--------- _Dominical_
_Year._
_Paschal_
_Easter._
_Epact._
_Golden_ _Letter._
_Full_
_Number._
_Moon._
-----------+-------+----------+---------+--------+--------- cb
1672
April 12
17
0
1 a
1673
” 1
2
11
2 g
1674
March 21
25
22
3 f
1675
April 9
14
3
4 ed
1676
March 29
5
14
5 c
1677
April 17
18
25
6 b
1678
” 6
10
6
7 a
1679
March 26
2
17
8 gf
1680
April 24
21
28
9 e
1681
” 3
6
9
10 d
1682
March 23
29
20
11 c
1683
April 11
18
1
12 ba
1684
March 31
2
12
13 g
1685
April 19
22
23
14 f
1686
” 8
14
4
15 e
1687
March 28
30
15
16 dc
1688
April 16
18
26
17 b
1689
” 5
10
7
18 a
1690
March 25
26
18
19 g
1691
April 12
15
0
1 fe
1692
” 1
6
11
2 d
1693
March 21
22
22
3 c
1694
April 9
11
3
4 b
1695
March 29
3
14
5 ag
1696
April 17
22
25
6 f
1697
” 6
7
6
7 e
1698
March 26
30
17
8 d
1699
April 14
19
28
9 c
1700
” 3
4
9
10 b
1701
March 23
27
20
11 a
1702
April 11
16
1
12 g
1703
March 31
1
12
13 fe
1704
April 19
20
23
14 d
1705
” 8
12
4
15 c
1706
March 28
4
15
16 b
1707
April 16
17
26
17 ag
1708
” 5
8
7
18 f
1709
March 25
31
18
19 -----------+-------+----------+---------+--------+---------
correction, that is, till the year 1900, a period of 190 years, when the intercalation being again suppressed, causes the first paschal moon of the cycle to fall on the 14th of April, and, of course, all the other moons of the cycle to fall one day later. The reason the correction is not made the first year of the century is, the lunar cycle must first be completed, and that did not occur until 1710. As 100 is not a multiple of 19, the number of years in the cycle, and, as the corrections
-----------+-------+----------+---------+--------+--------- _Dominical_
_Year._
_Paschal_
_Easter._
_Epact._
_Golden_ _Letter._
_Full_
_Number._
_Moon._
-----------+-------+----------+---------+--------+--------- e
1710
April 13
20
0
1 d
1711
” 2
5
11
2 cb
1712
March 22
27
22
3 a
1713
April 10
16
3
4 g
1714
March 30
1
14
5 f
1715
April 18
21
25
6 ed
1716
” 7
12
6
7 c
1717
March 27
28
17
8 b
1718
April 15
17
28
9 a
1719
” 4
9
9
10 gf
1720
March 24
31
20
11 e
1721
April 12
13
1
12 d
1722
” 1
5
12
13 c
1723
March 21
28
23
14 ba
1724
April 9
16
4
15 g
1725
March 29
1
15
16 f
1726
April 17
21
26
17 e
1727
” 6
13
7
18 dc
1728
March 26
28
18
19 b
1729
April 13
17
0
1 a
1730
” 2
9
11
2 g
1731
March 22
25
22
3 fe
1732
April 10
13
3
4 d
1733
March 30
5
14
5 c
1734
April 18
25
25
6 b
1735
” 7
10
6
7 ag
1736
March 27
1
17
8 f
1737
April 15
21
28
9 e
1738
” 4
6
9
10 d
1739
March 24
29
20
11 cb
1740
April 12
17
1
12 a
1741
” 1
2
12
13 g
1742
March 21
25
23
14 f
1743
April 9
14
4
15 ed
1744
March 29
5
15
16 c
1745
April 17
18
26
17 b
1746
” 6
10
7
18 a
1747
March 26
2
18
19 -----------+-------+----------+---------+--------+---------
cannot be made only at the beginning of the cycle, so they cannot be made the first year of the century only once in 1900 years. It may be seen from one of the above tables that the correction is made in the year 1900, for the reason that that is the first century which is a multiple of 19. The next centurial year that is exactly divisible by 19, is 3800. Therefore, none of the corrections for the next 1900 years, will occur on the first year of the century. It may also be seen from
-----------+-------+----------+---------+--------+--------- _Dominical_
_Year._
_Paschal_
_Easter._
_Epact._
_Golden_ _Letter._
_Full_
_Number._
_Moon._
-----------+-------+----------+---------+--------+--------- gf
1748
April 13
14
0
1 e
1749
” 2
6
11
2 d
1750
March 22
29
22
3 c
1751
April 10
11
3
4 ba
1752
March 30
2
14
5 g
1753
April 18
22
25
6 f
1754
” 7
14
6
7 e
1755
March 27
30
17
8 dc
1756
April 15
18
28
9 b
1757
” 4
10
9
10 a
1758
March 24
26
20
11 g
1759
April 12
15
1
12 fe
1760
” 1
6
12
13 d
1761
March 21
22
23
14 c
1762
April 9
11
4
15 b
1763
March 29
3
15
16 ag
1764
April 17
22
26
17 f
1765
” 6
7
7
18 e
1766
March 26
30
18
19 d
1767
April 13
19
0
1 cb
1768
” 2
3
11
2 a
1769
March 22
26
22
3 g
1770
April 10
15
3
4 f
1771
March 30
31
14
5 ed
1772
April 18
19
25
6 c
1773
” 7
11
6
7 b
1774
March 27
3
17
8 a
1775
April 15
16
28
9 gf
1776
” 4
7
9
10 e
1777
March 24
30
20
11 d
1778
April 12
19
1
12 c
1779
” 1
4
12
13 ba
1780
March 21
26
23
14 g
1781
April 9
15
4
15 f
1782
March 29
31
15
16 e
1783
April 17
20
26
17 dc
1784
” 6
11
7
18 b
1785
March 26
27
18
19 ----------+-------+----------+---------+--------+----------
the above tables, that, though the intercalary day was suppressed in the year 1800, no change is made in the date of the paschal moon. The reason is, the lunar equation also occurred; while the former correction would cause the paschal moon to fall one day later, that is on the 14th day of April, the latter would make it fall one day earlier, that is on the 12th; so they compensate each other, and there is no correction to be made until the year 1900, when the solar equation
-----------+-------+----------+---------+--------+--------- _Dominical_
_Year._
_Paschal_
_Easter._
_Epact._
_Golden_ _Letter._
_Full_
_Number._
_Moon._
-----------+-------+----------+---------+--------+--------- a
1786
April 13
16
0
1 g
1787
” 2
8
11
2 fe
1788
March 22
23
22
3 d
1789
April 10
12
3
4 c
1790
March 30
4
14
5 b
1791
April 18
24
25
6 ag
1792
” 7
8
6
7 f
1793
March 27
31
17
8 e
1794
April 15
20
28
9 d
1795
” 4
5
9
10 cb
1796
March 24
27
20
11 a
1797
April 12
16
1
12 g
1798
” 1
8
12
13 f
1799
March 21
24
23
14 e
1800
April 9
13
4
15 d
1801
March 29
5
15
16 c
1802
April 17
18
26
17 b
1803
” 6
10
7
18 ag
1804
March 26
1
18
19 f
1805
April 13
14
0
1 e
1806
” 2
6
11
2 d
1807
March 22
29
22
3 cb
1808
April 10
17
3
4 a
1809
March 30
2
14
5 g
1810
April 18
22
25
6 f
1811
” 7
14
6
7 ed
1812
March 27
29
17
8 c
1813
April 15
18
28
9 b
1814
” 4
10
9
10 a
1815
March 24
26
20
11 gf
1816
April 12
14
1
12 e
1817
” 1
6
12
13 d
1818
March 21
22
23
14 c
1819
April 9
11
4
15 ba
1820
March 29
2
15
16 g
1821
April 17
22
26
17 f
1822
” 6
7
7
18 e
1823
March 26
30
18
19 ----------+-------+----------+---------+--------+----------
again occurs, and the first paschal moon of the cycle falls on the 14th; which cycle is repeated sixteen times in a period of 304 years, after which, in 2204, the date of the first paschal moon is the 15th of April.
The reason there is no correction to make in this long period is, first, the year 2000 is a common year in the Gregorian calendar; second, in the year 2100 both the solar and the lunar equations again occur, and occurring together, they compensate each other; consequently
-----------+-------+----------+---------+--------+--------- _Dominical_
_Year._
_Paschal_
_Easter._
_Epact._
_Golden_ _Letter._
_Full_
_Number._
_Moon._
-----------+-------+----------+---------+--------+--------- dc
1824
April 13
17
0
1 b
1825
” 2
2
11
2 a
1826
March 22
25
22
3 g
1827
April 10
14
3
4 fe
1828
March 30
5
14
5 d
1829
April 18
18
25
6 c
1830
” 7
10
6
7 b
1831
March 27
2
17
8 ag
1832
April 15
21
28
9 f
1833
” 4
6
9
10 e
1834
March 24
29
20
11 d
1835
April 12
18
1
12 cb
1836
” 1
2
12
13 a
1837
March 21
22
23
14 g
1838
” 9
14
4
15 f
1839
March 29
30
15
16 ed
1840
April 17
18
26
17 c
1841
” 6
10
7
18 b
1842
March 26
26
18
19 a
1843
April 13
15
0
1 gf
1844
” 2
6
11
2 e
1845
March 22
22
22
3 d
1846
April 10
11
3
4 c
1847
March 30
3
14
5 ba
1848
April 18
22
25
6 g
1849
” 7
7
6
7 f
1850
March 27
30
17
8 e
1851
April 15
19
28
9 dc
1852
” 4
4
9
10 b
1853
March 24
27
20
11 a
1854
April 12
16
1
12 g
1855
” 1
1
12
13 fe
1856
March 21
20
23
14 d
1857
” 9
12
4
15 c
1858
March 29
4
15
16 b
1859
April 17
17
26
17 ag
1860
” 6
8
7
18 f
1861
March 26
31
18
19 ----------+-------+----------+---------+--------+----------
the cycle is continued until 2204, after which, as has already been stated, the date of the first paschal moon is the 15th of April. This cycle is repeated six times in a period of 114 years, when in 2318, for reasons already given, the date of the first paschal moon of the next cycle falls on the 16th, and is repeated five times in a period of 95 years, when, in 2413, the lunar equation occurs alone, and the date of the first paschal moon for the next 95 years, that is till the year 2508,
-----------+-------+----------+---------+--------+--------- _Dominical_
_Year._
_Paschal_
_Easter._
_Epact._
_Golden_ _Letter._
_Full_
_Number._
_Moon._
-----------+-------+----------+---------+--------+--------- e
1862
April 13
20
0
1 d
1863
” 2
5
11
2 cb
1864
March 22
27
22
3 a
1865
April 10
16
3
4 g
1866
March 30
1
14
5 f
1867
April 18
21
25
6 ed
1868
” 7
12
6
7 c
1869
March 27
28
17
8 b
1870
April 15
17
28
9 a
1871
” 4
9
9
10 gf
1872
March 24
31
20
11 e
1873
April 12
13
1
12 d
1874
” 1
5
12
13 c
1875
March 21
28
23
14 ba
1876
April 9
16
4
15 g
1877
March 29
1
15
16 f
1878
April 17
21
26
17 e
1879
” 6
13
7
18 dc
1880
March 26
28