2 articles for "Epact"

**Epact**[Astro*Index]

(Greek)

The age of the Moon, diminished by one day, on January 01 in the Gregorian Ecclesiastical Lunar Calendar. This value is not always the same as the tabular age on December 31 of the preceding year; a discrepancy of two days is possible. In tables issued by Pope Gregory XIII, the date of Easter is determined using the Epact, rather than the Golden Number.

See also:

♦ Lunar ♦ Gregorian Calendar ♦ Ecclesiastical Calendar ♦ Easter

**Epact**[DeVore]

A word of Greek origin, applied to a number that indicates the Moon's age on the first day of the year. As the common solar year is 365 d., and the lunar year 354 d., the difference of 11 indicates that if a new moon falls on January 1st in any year, it will be 11 days old on the first day of the next year, and 22 days old on the first of the third year. Hence the epacts of those years are numbers 11 and 22. In a leap year, however, the remainder is lo, which introduces such complexities that the chief and almost sole use of the epact is in determining the date of Easter. A number which represents the number of days of excess of the Solar year over 12 lunar months is the annual epact. The number which represents the number of days of excess of a calendar month over a lunar month is the monthly epact. The epacts differ from the Golden Numbers, from which they are derived, in that they provide for the adjustment of (1) the solar equation, a correction of the Julian Calendar, and (2) the lunar equation, a correction of the error in the lunar cycle. In its use in determining the date of Easter, apparently more concern was paid to the consideration that it must not coincide with the Passover than to astronomical exactness, for the Tables of Epacts are frequently in error by as much as two days earlier or later. For Tables of Easter dates v. Easter.

See also:

♦ Lunar ♦ Gregorian Calendar ♦ Ecclesiastical Calendar ♦ Easter

Astro*Index Copyright © 1997 Michael Erlewine