Talk:Epact

message: In the Preface in the Book of Common Prayer of the Church of England, in a section decreed by the Calendar Act, there is a page listing the Moveable Feasts for about 40-50 years.  Its third column contains Epacts.  The Act and Book do not seem to have any definition of the Epact.  Just what formal definition does the Church use?
Note that such a table is in Statutes at Large 1765, but not in the database which represents the Act as amended to date.
I suggest that the Article should contain a short section explicitly answering this point.
82.163.24.100 (talk) 10:01, 3 May 2008 (UTC)
thread_title:  Epacts in Book of Common Prayer 

message: The current article text under "Lilian (Gregorian) epacts" 
*(a) seems to get it just right where it comes to the actual rules of the solar equation and lunar equation; but 
*(b) it also contains a quantity of material that seems completely unsupported, and at best dubious, where it comes to the 'Metonic relation', 'pure' or otherwise, and to the unit called the 'tithi'.
I suggest that the relevant sources here are those that refer to the actual work that culminated in the Gregorian reform of 1582, especially the papers given in the 1983 commemorative conference.  These sources (primarily the papers by O Pedersen, J D North, G Moyer and A Ziggelaar) appear to show that the lunar equation in the Lilian system of epacts was a systematic empirical adjustment, intended to reflect the fact that the Moon's mean rate of motion had turned out to be just a little faster than the expectation embodied in the traditional form of 19-year cycle. In the second half of the sixteenth century, full moons were occurring much sooner than the dates indicated on the traditional tabular basis (which by then had been in use for over a thousand years). According to the text of "Inter gravissimas" the paschal full moons needed to be "put back in place" from a deviation of something more than 4 days ("et XIV paschalem suo in loco, a quo quatuor et eo amplius dies hoc tempore distat, reponendam".)  Lilius' periodical adjustment was intended as a correction to bring the tabular epact value closer to the real age of the Moon, and prevent any repeat of the long-term divergence which had been seen with the traditional tables.  
A temporary 'patch' had been applied in the 1568 edition of the Breviary, namely, to move the Golden Numbers up four places and to warn that they would need to be reviewed again and moved every 300 years or so.  But the text of "Inter gravissimas" complains that previously-proposed solutions were not long-term ("neque perennes erant"), and it praises Lilio's effort for providing in principle a perpetual arrangement to restore "all the things in the calendar that had got into disarray" so that there would be no future "mutation" ("omnia quæ in calendario collapsa sunt, constanti ratione et sæculis omnibus duratura, sic restitui posse ostendit ut calendarium ipsum nulli umquam mutationi in posterum expositum esse videatur.").  
In all of this there seems to be no reference to Metonic relations or tithis.  It seems appropriate to take out the material about these factors, unless good sources are given for their relevance to the 16th-century work. Terry0051 (talk) 01:01, 4 December 2009 (UTC)
replies: text: Terry, I notice your edit a bit late.  I think you misunderstand.  Your text does not explain why the reformers bothered to have both a solar equation and a lunar equation, instead of just 43 epact adjustments evenly spread over 10000 years.  The only explanation I can think of is that they tried to undo the effect of the skipped Gregorian leap days, and then adjust the ratio of the synodic month to the (Julian) calendar year.  But as explained, if this was their intention, then it is mistaken.  It is a mathematical fact, as explained in my text in 2 different ways, that Lilian epact corrections are 1/30th of a synodic month, and not full days on average.  Unfortunately, both in the Canons and in his explicatio, Clavius explains the use of the epacts but is vague on the reasons and background of the construction.  Likewise the commemorative conferences spent much attention to the tropical year and the solar calendar and the history of the computus, but lacks a thorough analysis of the lunar calendar.
Tom Peters (talk) 10:22, 20 February 2010 (UTC)
thread_title:  Lilian (Gregorian) epacts 

message: The word 'computistical is used a number of times in this article.  Does anyone out there know what this word means?Duncan.france (talk) 00:58, 19 October 2018 (UTC)
thread_title: 'Computistical' - What does this mean?

message: At present, the section Solar and lunar years begins:
Is the reference to a single leap day every three years correct? It certainly would not bring the lunar year back into synchronisation with the solar year. Later in the section, there is a much more convincing statement:
 
and at the Intercalation article, the section on lunisolar calendars says
In a nutshell, I really can't make sense of the statement that a single leap day is added every three years. What am I missing? --John Maynard Friedman (talk) 16:41, 4 October 2021 (UTC)
thread_title:  Leap day or leap month? 

message: In this article and at Gregorian calendar, the decision to change the base to 1 January is either uncited or inadequately cited. The info needed is almost certainly somewhere in the Canons that accompanied Inter gravissimas, specifically this one:
*  
So all we need is a medievalist who can find out exactly where. 
If it helps to show that the work is likely to be fruitful, the preceding Canon has the gem
(which, after I corrected the mistranscription of  as  and a few other obvious typos, Google translate made an astonishingly good job of converting into credible English). But to transcribe and google-translate the whole chapter would take more time that I am willing to give. 𝕁𝕄𝔽 (talk) 10:20, 23 April 2023 (UTC)
replies: text: On further consideration, I decided to remove discussion of the epact from the Gregorian Calendar article as being too detailed and arguably off-topic. So I have no further interest in this translation but decided to leave the citation here in case anyone has other reasons to investigate further. --𝕁𝕄𝔽 (talk) 10:54, 23 April 2023 (UTC)
thread_title:  Does anyone here speak medieval Latin?