|
|
|
|
|
|
|
changes was made which mandated changes in epact at the end of seven successive 300-year periods and once at the end of a 400-year period. The most correct result was established by fixing the end of one of the 2,500-year periods at the end of the year A.D. 1800. The resulting correction tables were thus produced: |
|
|
|
|
Correction to Epact
for Intercalation | Correction to Epact
for the Lunar Cycle | | Year | Correction | Year | Correction | | 1700 | | | | | 1800 | | 1800 | | | 1900 | | | | | 2100 | | 2100 | | | 2200 | | | | | 2300 | | | | | | 2400 | | | 2500 | | | | | | 2700 | | | | 3000 | | | | 3300 | | | | 3600 | |
|
|
|
|
|
|
When the changes in the factors coincide in the same year, as in 1800 and 2100, no change is made. |
|
|
|
|
|
|
|
|
The value of epact can range over the number of days in a full lunar month, from one through 30. The moon's age in days is the epact of the following year. For example, if the last lunation ends on 2 December, then the last new moon starts on 3 December. The age of the moon on 31 December is 31 2 = 29 days, so the epact of the following year is 29. If the new year to which epact applies is one of the years in one of the tables, the value is altered accordingly. |
|
|
|
|
|
|
|
|
The principal use of epact is the determination of Easter date. Although the true vernal equinox can occur as much as two days early in the Gregorian calendar, the calendar equinox of 21 March is the determining factor. The complex system devised by Lilius ensures that the date of Easter can be determined without recourse to astronomical observation. Even the prohibition against coincidence with Jewish Passover was taken into consideration. |
|
|
|
|
|
|
|
|
9.1.4.4.3
Dominical Letter |
|
|
|
|
|
|
|
|
The omission of leap year in century years also altered the calculation of the dominical letter from its simpler Julian pattern, in which the pattern, of year structures was repeated with a period of 28 years. |
|
|
|
|
|