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Epact
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{{short description|Age of a phase of the moon in days, and method}} {{more citations needed|date=May 2018}} [[File:Lier Zimmertoren Clock detail 06.JPG|thumb|Face on the [[Zimmer tower]] in [[Lier, Belgium]]: On the outer ring, the hand points to the [[golden number (time)|golden number]], or the number of the current year in the [[metonic cycle]]. The inner ring shows the epact, which is the age of the moon on the first of January of the current year.]] The '''epact''' ({{langx|la|epactae}}, from {{langx|grc|ἐπακται ἡμεραι}} ({{Transliteration|grc|epaktai hēmerai}}) = added days) used to be described by medieval [[Computus|computists]] as the age of a [[Lunar phase|phase of the Moon]] in days on 22 March;<ref>{{ Citation | author = Bede the Venerable | author-link = Bede | translator-last = Wallis | translator-first = Faith | title = The Reckoning of Time | chapter = Lunar Epacts | series = Translated Texts for Historians | volume = 29 | publisher = Liverpool University Press | place = Liverpool | date = 1999 | orig-date = 725 | page = 131 | isbn = 0-85323-693-3 | quote = The epacts noted in the 19-year cycle specifically stand for the age of the moon on the 11th kalends of April [22 March], the beginning of the Paschal feast.}}</ref> in the newer [[Gregorian calendar]], however, the epact is reckoned as the age of the [[Ecclesiastical new moon|ecclesiastical moon]] on 1 January.<ref>{{Citation | last = Richards | first = E. G. | editor-last = Urban | editor-first = S. E. | editor2-last = Seidelman | editor2-first = P. K. | date = 2012 | title = Explanatory Supplement to the Astronomical Almanac | chapter = Calendars | publisher = University Science Books | place = Mill Valley, CA | pages = 599–601 | isbn = 978-1-891389-85-6 | chapter-url = http://aa.usno.navy.mil/publications/docs/c15_usb_online.pdf | quote = The Epact of a year … is the age in days (0 to 29) of the ecclesiastical moon on the first day of the year (January 1). | access-date = 2017-01-24 | archive-date = 2019-04-30 | archive-url = https://web.archive.org/web/20190430134555/http://aa.usno.navy.mil/publications/docs/c15_usb_online.pdf }}</ref> Its principal use is in determining the [[date of Easter]] by computistical methods. It varies (usually by 11 days) from year to year, because of the difference between the solar year of 365{{ndash}}366 days and the lunar year of 354{{ndash}}355 days.<ref>[http://henk-reints.nl/cal/audette/canon2.html Latin text and French translation of the Second Canon of the Gregorian calendar]</ref>
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