Talk:Enoch calendar

as accurate as the julian calendar?

adding 7 days every 7 years to a 364 day calendar does not make it as accurate as the julian calendar of 364.25 days. Em3ryguy (talk) 13:57, 19 March 2009 (UTC)

You're right, but it's all just idle speculation anyway -- nothing is said about intercalation in the ancient texts... AnonMoos (talk) 14:06, 19 March 2009 (UTC)

That's true, so I'm going to look at the article in the Monthly again. What's here probably doesn't accurately reflect what's there, since such a gross error would probably not have been published in such a place. Michael Hardy (talk) 18:08, 19 March 2009 (UTC)

OK, I've looked at the article. One extra week every seven years, except that there would be two extra weeks every fourth "Saturday year", i.e. every 28 years. Then it's as accurate as the Julian calendar. You see: makes every quarter start on the first day of the week while still being as accurate as the Julian Calendar. The he adds a bit more elaboration to make it more accurate than the Gregorian calendar. Michael Hardy (talk) 22:15, 19 March 2009 (UTC)

Does the beyond-Julian stuff have to be included at all? It's apparently just the personal speculations of one guy -- speculations which I regard as historically quite problematic, since the information necessary to go beyond the Julian calendar in accuracy was only known to a relatively small number of Greek or Babylonian astronomers, and was completely ignored by Julius Caesar in his calendar reform of ca. 45 B.C. Apocalyptic-minded Jews were not generally closely tied into to the latest Greek and Babylonian intellectual and scientific developments -- especially in this case, since Greek and Babylonian astronomy were heavily intertwined with astrology and astral mysticism, which were objectionable from a Jewish religious viewpoint. AnonMoos (talk) 02:40, 20 March 2009 (UTC)

Also, claims of being "more accurate than Gregorian" are often inaccurate because the calculations are being made on the basis of the mean tropical year, while the Gregorian calendar was actually meant to approximate the vernal equinox year (the Revised Julian Calendar is one example of a calendar which has been claimed to be more accurate than Gregorian, but isn't really, when the vernal equinox year is used as the basis). Anyway, once you get into corrections of one day in several thousand years, slight changes in day length mean that no fixed formula can be accurate over the long term... AnonMoos (talk) 12:29, 21 March 2009 (UTC)

further problem

I'm looking at Mapping Time: The Calendar and Its History by E. G. Richards, and there's no speculation about intercalation methods at all. AnonMoos (talk) 12:45, 21 March 2009 (UTC)

A better rational ratio for year length.

The mean tropical year on January 1, 2000 was 365.2421897 or 365 ephemeris days, 5 hours, 48 minutes, 45.19 seconds. This changes slowly; an expression suitable for calculating the length of a tropical year in ephemeris days, between 8000 BC and 12000 AD is

  365.2421896698 - 6.15359 x 10^-6 x T - 7.29 x 10^-10 x T^2 + 2.64 x 10^-10 x T^3

where T is in Julian centuries of 36,525 days of 86,400 SI seconds measured from noon January 1, 2000. (cf: <<https://en.wikipedia.org/wiki/Tropical_year#Mean_tropical_year_current_value>>)

So taking 365.2421897, and find the best rational ratio, we get 365 + 31/128 = 365.2421875. This leaves an error in the fractional part of just under 0.19 seconds.

So there is a residual error, using this ratio, of just under one second every five years.

Thus the residual error of one day would occur every 432,000 years, all other things being equal. — Preceding unsigned comment added by Daveat168 (talk • contribs) 17:30, 15 October 2019 (UTC)

The Julian year is 365.25 days, which is then 365 + 32/128 This then means that, to the exactness above, every 128 years, the Julian calendar is out by one day. That is, every 128 years, a leap-year-day needs to be skipped. In other words, every 32nd leap-year-day needs to be skipped.

So this would be the new method, which I would recommend:

Divide the year number by 4. If the remainder is zero, then it is a leap year, unless,

Divide the quotient by 32. If the remainder is zero, then it is not a leap year. — Preceding unsigned comment added by Daveat168 (talk • contribs) 17:58, 13 October 2019 (UTC)

The Enoch calendar, though, only intercalated weeks. So the double leap-year-week, which happened every 28 years, needs to be skipped once in every 32 28 year periods. So 32 x 28 = 896. So every 896 years, the double leap-year-week is replaced by a single leap-year-week.

Interestingly, 896 = 7 x 2^7, so this would be a highly significant number to a society deeply involved with the number 7. The calendar is attributed to Enoch. Enoch was the father of Methuselah, who lived for 969 years, we are told.

No, 896 is not equal to 969, but both are quite close to 900, which was the popular approximation, So is this the reason why the Enoch calendar is so attributed, and was the great cycle of 896 years referred to as a Methuselah?

Dave at 168 10:43, 7 October 2019 (UTC)

When the Book of Enoch was being written, knowledge of year-length approximations more accurate than 365.25 was basically confined to professional astronomers. At the time, astronomy was not clearly distinguished from astrology, and astrology had come close to displacing traditional Greek religion among many Greeks and persons influenced by Greek culture, so that apocalyptic Jews did not associate closely with astronomers/astrologers (in fact Jews had a special insulting term for pagans, "worshipper of stars and constellations"). Also, the concept of "mean tropical year" was then unknown... AnonMoos (talk) 07:13, 14 October 2019 (UTC)