Talk:Epact

The section on the age of the moon is not aparently NPOV. So I have moved it here.

It asserts that the age of the moon equals the day of the lunation. Also the concluding paragraph contradicts the Catholic encyclopeadia article referenced and the end of the article.

I observe that an epact of "*" (0 or 30 or nulla) for a year, implies a 1st day of the lunar month on the 1st day of the year. If the epact is an age, this would mean that the age is 0 on day 1. Hardly consistent. All this involves the usual confusion between ordinal counting and cardinal (or real) numbers - people used to be "in their first year", nowadays your age is 1 year *after completing* your 1st year. So what is the age of the Moon on the 1st day of the month, traditionally? For that matter, what is the age of J.C. today? This is related to the milennium controversy (was 1 Jan 2000 or 1 Jan 2001 the start of "the" new milennium?).

And incidentally, the Catholic Encyclopedia can have it wrong too... -- Tom Peters 13:07, 15 Aug 2003 (UTC)

age of the Moon

The epact is often defined as the age of the Moon at the begin of the (solar) year. Now when a new lunar month begins on 1 January, the epact is 0. However we count the days of the lunar calendar as ordinal numbers, i.e. in this case the 1st day of January is also the 1st day of the lunar year and the 1st day of the lunar month. We can accordingly assign an age of 1 day to the Moon, if we follow the ancient convention that the lunar month starts when the New Moon is first visible. This is actually some time after the astronomical conjunction of Sun and Moon (also called Dark Moon), when the "astronomical age of the Moon" is 0. Indeed the lunar calendar used for Calculating the date of Easter in the Gregorian calendar has its months starting systematically a day after the astronomical New Moon. In this reckoning the astronomical opposition of Sun and Moon indeed usually falls on the 14th day of the lunar month, which is consistent with the tradition of having the Paschal Full Moon on the 14th day of the spring month.

The epact can then be defined as the age of the Moon on the day before the begin of the (solar) year. This is not the same as the age of the Moon on the last day of the previous year, because the epact may be corrected by 1 at the start of the new year.

Karl August 15 10h UT