from The American Heritage® Dictionary of the English Language, 5th Edition.
- noun The period of time necessary to bring the solar calendar into harmony with the lunar calendar.
from The Century Dictionary.
- noun The excess of a solar over a lunar year or month. Hence, usually A number attached to a year by a rule of the calendar to show the age, in days completed and commenced, of the calendar moon at the beginning of the year—that is, on January 1st in the Gregorian, Victorian, and early Latin calendars, or March 22d in the Dionysian calendar, or old style.
from the GNU version of the Collaborative International Dictionary of English.
- noun (Chron.) The moon's age at the beginning of the calendar year, or the number of days by which the last new moon has preceded the beginning of the year.
- noun the excess of the solar year over the lunar year, -- being eleven days.
- noun the excess of a calendar month over a lunar.
from Wiktionary, Creative Commons Attribution/Share-Alike License.
- noun the time (number of days) by which a
solar yearexceeds twelve lunar months; it is used in the calculation of the date of Easter
from The American Heritage® Dictionary of the English Language, 4th Edition
When the epact of the year is known, the days on which the new moons occur throughout the whole year are shown by Table IV., which is called the
In consequence of the solar and lunar equations, it is evident that the epact or moon's age at the beginning of the year, must, in the course of centuries, have all different values from one to thirty inclusive, corresponding to the days in a full lunar month.
The epact of the year, therefore, or 19, must stand beside that day, whereas, according to the regular order, the epact corresponding to the
The 2nd of January is therefore the day [v. 04 p. 0996] of the new moon, which is indicated by the epact twenty-nine.
In the calendar this epact first occurs before the 2nd of December at the 26th of November.
The epact 19 '(also distinguished by an accent or different character) is placed in the same line with 20 at the 31st of December.
In Table III, under 9, and in the line C, we find the epact
Osiris, and winning from her the five days of the epact, which were added to complete the 365 days of the year.
When P = 2 the new moon falls on the ninth, and the epact is consequently twenty-two; and, in general, when P becomes 1 + x, E becomes 23 - x, therefore P + E = 1 + x + 23 - x = 24, and
On account of the solar equation S, the epact J must be diminished by unity every centesimal year, excepting always the fourth.