Talk:Leap week calendar

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Leap year rule[edit]

The rule determining whether a year has 53 weeks, will be more complicated than a leap year rule, especially if the variation of the equinox and solstice dates is less than two weeks.

Incorrect. Gregorian-level accuracy can be achieved with this simple rule: Leap weeks are added in multiples of 5 except for multiples of 40 not divisible by 400.

Yes, but this rule gives rise to a variation in excess of two weeks see [[1]]. That is why I added the especially clause. It is also a slightly more complicated than the Gregorian rule, from using a 40 rather than 100 year period for the exceptions. Karl (talk) 13:11, 25 January 2013 (UTC)
Inherently a leap week calendar has greater equinox or solstice wobble than a leap day calendar, but that can be minimized by using a leap rule that distributes the leap years as smoothly as possible, which is simpler to do anyway. Furthermore, there are astronomical advantages in distributing the leap years symmetrically within each leap cycle, which is also no more complex to accomplish, see Symmetrical Leap Cycles. If you are really determined to use a 400-year leap cycle, and I don't recommend it because it yields a calendar mean year that is slightly too long relative to the mean northward equinoctial year that is typically taken as the target, then there must be 71 leap weeks per cycle. It can't be a perfectly symmetrical cycle because 400 is an even number, but it can be made almost perfectly symmetrical and leap years smoothly distributed by the simple single-step leap rule: Year y is leap only if the remainder of (71 y + 200) / 400 < 71. Kalendis (talk) 21:18, 1 April 2011 (UTC)
That is, year y is a leap year only if "mod(71y+200,400)<71" is true. Cup o' Java (talkcontribs) 21:25, 24 January 2013 (UTC)

Equal complexity to the Gregorian calendar's leap day rule.

I was just about to make the same coment. Let's remove this line, shall we? By the way, I do wonder what the equinoxes and solstices have to do with it. Jimp 7Sep05
Normally a calendar mean year is designed to approximate an equinoctial or solstitial mean year to minimize long-term drift of the calendar relative to the target equinox or solstice. In the present era the only sensible choices for a simple fixed arithmetic leap cycle are the mean northward equinoctial year or the mean north solstitial year, as they are currently stable. By contrast, the mean southward equinoctial year and south solstitial year are currently getting progressively shorter, see: The Lengths of the Seasons (on Earth). Kalendis (talk) 21:22, 1 April 2011 (UTC)
The whole concept of leap week has a problem that equinoxes and solstices are not on the same day every year. Depending on which calendar to use, they can vary from 3 days up to 19 days. It can be a significant problem in computing Easter as March equinox has to be on March 21. --Quest for Truth (talk) 14:48, 22 March 2009 (UTC)
False. The equinox does not, in fact, have to be March 21, and, in fact, it is not always March 21 in the Gregorian calendar. Victor Engel (talk) 15:42, 30 March 2011 (UTC)
True, there is greater variation in the dates of equinoxes and solstices (but, as noted above, variation exists in the Gregorian calendar) but how big a problem is this? Easter is unimportant to two-thirds of the World's population and, as for the rest, I'm sure they won't be too fussed if it were moved from the first Sabbath day once the Moon hath waxen full since the equinox of March to, say, the eighth of April (if they even notice). JIMp talk·cont 07:49, 22 January 2013 (UTC)

External links: ISO leap years link wrong[edit]

The lnk goes to the CCC&T site, and lists leap weeks according to that calendar. This is wrong because different leap year rules were used to derive the list (CCC&T uses unspecified astronomical data - ISO 8601 is derived from the underlying gregorian year) and because the CCC&T calendar begins on Sunday rather than Monday, meaning that start dates cannot be matched.

Renaming Leap Week Calendar to Week Calendar[edit]

What is the reason for renaming the article? I note that related links in the newly renamed article still refer to "Leap Week Calendar" rather than "Week Calendar". I see no compelling reason to have changed the name, but maybe I'm missing something. Victor Engel (talk) 14:26, 31 March 2011 (UTC)

I agree. A calendar that uses a leap week is a leap week calendar, a calendar that uses a leap day is a leap day calendar, and a calendar that uses a leap month is a leap month calendar. One can equally well use a skip week, skip day, or skip month calendar with the same duration leap cycles, it doesn't change how many years are long vs. short. Leaps per Cycle = Years per Cycle minus Skips per Cycle. Kalendis (talk) 21:09, 1 April 2011 (UTC)

There is no adequate week calendar article yet. Leap week calendars are a special kind of week calendars, i.e. all leap week calendars are week calendars, but not all week calendars have a leap week. Instead of writing a new article from scratch it made sense to me to extend this one (and therefore first rename, i.e. move it).
WP:PRECISION quoted in the revert of the move doesn’t apply, because the change is not about a controversial title or something like that, but founded in changing the scope.
It's not controversial to you because you dreamed it up. Can you even cite any references that use the term "week calendar"? Victor Engel (talk) 04:14, 2 April 2011 (UTC)
Lastly, although I do use the term some people object to “leap week”, “leap week year” and “leap week calendar”, since they only consider “leap” valid in combination with 29 February. See the version history of ISO week date that resulted in “long year”.
That, of course, presumes the calendar under consideration even has such a date as 29 February. It may not. I'm not sure what relevance a discussion on ISO week date has. As mentioned in that article, that is a special case of a leap week calendar, so there may be things specific to it. On the flip side, I don't think it's a given, either, that a leap week calendar must have weeks consisting of 7 days. Suppose a calendar was made up of 6 day weeks. A short year then might have 60 weeks, and a long year 61 weeks. In such a calendar, week 53 really has no special meaning at all. Victor Engel (talk) 04:30, 2 April 2011 (UTC)
Anyhow, I actually have more important things to care about at the moment. — Christoph Päper 23:31, 1 April 2011 (UTC)
Yeah, you said something like that before, and then proceeded to amend the article. Victor Engel (talk) 04:14, 2 April 2011 (UTC)
FWIW, “week calendar” is better established than “leap week calendar”: “week calendar” wins Google battle, over two magnitudes.Christoph Päper 13:00, 2 April 2011 (UTC)


One of the advantages is apparently "For leap week calendars without months, each date of the year can be completely specified with three data (week, weekday, year), instead of four (weekday, month, ordinal day, year)." Call me old fashioned, but I only need 3 pieces of data NOW to reference any day in any year. Day of month, month, and year. MrZoolook (talk) 00:28, 14 January 2013 (UTC)

I agree. This should be changed. Feel free to go a head and be bold! –Cup o' Java (talkcontribs) 01:27, 15 January 2013 (UTC)
That's what I was thinking. Jimp 10:38, 19 March 2014 (UTC)
Agreed. I remove the sentence, as there is no advantage (three data for both). Kiwipidae (talk) 10:29, 21 October 2017 (UTC)

Complicated leap-year rules[edit]

Says the article "Leap-year rules are usually more complicated than the Gregorian rule—except for the ISO Week Date, which follows the Gregorian calendar, having no leap-year rule of its own.".

What kind of exception is this? You have to figure out what day the Gregorian year starts on. To do that you have to use the Gregorian rule to figure out leap years but your not finished, you then have to figure out what day the Gregorian year would start on. It is a rule of its own, a very complicated rule.

There is, however, a simple rule which gives average years of a reasonable length (I don't know whether any notable proposal suggests it, though). We could switch the 4, 100 & 400 of the Gregorian with 5, 40 & 400. This rule is just as simple and gives a year just as long. Jimp 10:38, 19 March 2014 (UTC)

Notice that 1/4-1/100+1/400 = 97/400, while 1/5-1/40+1/400 = 71/400. Kiwipidae (talk) 23:22, 20 November 2017 (UTC)
Yes, there are 97 leap days or 71 leap weeks per 400-year cycle. 400 * 365 + 97 = 400 * 52*7 + 71*7
5:40:400 was proposed (at least) by Rick McCarty for his Weekdate calendar design. — Christoph Päper 08:59, 21 November 2017 (UTC)
5:40:400 is not used in Rick McCarty's Weekdate calendar. One criticism of 5:40:400 is that it varies 17 days against the Gregorian calendar rather than 7 days as the ISO week date does. The Weekdate calendar has this variation reduced somewhat by having a more complicated rule in which the exceptions (to a leap year once every 5 years) occur in intervals of 40, 45 or 50 years. - Karl (talk) 12:45, 21 November 2017 (UTC)
Karl is correct, although Weekdate uses a 400-year leap cycle with a regular leap week every 5 years, its exceptions are more smoothly distributed. James Reich uses 5:40:400 for the New Earth Calendar. Robert McClennon also used it or his Common-Civil-Calendar-and-Time Calendar and this was a (or even the) major difference to the Hanke-Henry Permanent Calendar, which Dick Henry explicitly based upon CCC&T. I may have confused the Scottish names. — Christoph Päper 02:35, 22 November 2017 (UTC)
Apples are being compared with oranges here. One leap day in five years is eighty in 400, less ten for the 40 - year exception makes seventy, and plus one for the 400 - year exception makes 71. In terms of the mean calendar year that's 365 + (71/400) = 365.1775 days. Compare that to the mean tropical year and this calendar will slip back by one day every fifteen years. At Wikipedia:Reference desk/Archives/Miscellaneous/2017 October 31#Which is the correct Potrzebie date? there's mention of a "Revised Gregorian calendar" which doesn't have a leap - year cycle so cannot go wrong. The article was in user space but has been deleted "G6:Housekeeping and routine (non-controversial) cleanup". It seems a suitable subject for inclusion in mainspace. Maybe one of the administrators who have edited this article @Michael Hardy: @Bryan Derksen: @Patrick: @Waldir: @Smjg: could do this? 2A00:23C0:8601:9701:8104:2131:4710:21B2 (talk) 14:48, 23 November 2017 (UTC)
You are mixing up your apples and oranges. 5:40:400 is a rule for leap weeks, not days. 364 + (71*7/400) = 365.2425 days. — Christoph Päper 15:07, 23 November 2017 (UTC)
  • Regarding the undeletion of User:Megalibrarygirl/Jacinto Quirarte: that's an interesting question. I see nothing in Wikipedia:Deletion policy or Wikipedia:Viewing and restoring deleted pages that would prevent another administrator to undelete a user subpage deleted by the user themselves. The former says: "Any user with a genuine reason to view a copy of a deleted page may request a temporary review (or simply ask an administrator to supply a copy of the page), and goes to further say that "these requests are likely to be denied if the content has been deleted on legal grounds (such as defamation or copyright violation), or if no good reason is given for the request" (emphasis mine), which doesn't seem to be the case here. The latter says "Only administrators, checkusers, and oversighters can view the content of deleted pages. This is considered necessary because deleted pages may contain copyright violations, personal information, libel, and so forth, and making such material publicly available could be problematic" − which, again, doesn't seem to be the case here.
    Having said that, I think the right thing to do, in the spirit of WP:IAR and WP:UCS, would be to obtain the permission from (or at the vert least give reasonable advance notice to) User:Megalibrarygirl before undeleting the page, even if just as a courtesy. --Waldir talk 15:56, 23 November 2017 (UTC)
@Waldir: I've been trying to clear out my subpages for a while. However, in this case, I got some strange information pasted into the article draft (which I no longer needed as Jacinto Quirarte is in the mainspace now), so I felt that I was being spammed. Deleting the page caused the spamming to stop. If you need to retrieve info from there, please undelete for now, but know that I will eventually be cleaning it out (eventually will take a long time), so it may be good to move it to another space. However, to address another issue involved, I'm flummoxed that anyone would need to retrieve my user draft about an art historian specializing in Chicano work in relation to leap years. It's confusing, but I don't want to obstruct anyone's work, either if it was accidentally pasted in my userspace. I hope that helps! Megalibrarygirl (talk) 15:13, 25 November 2017 (UTC)
Yeah, I found it odd as well :) Ok, given your consent, I'll restore the page, with the caveat to those looking into recovering information from it that it might get deleted soon. Ideally, the anonymous editor above can navigate the history and copy the relevant content here, so that your userspace can be unburdened of that subpage. --Waldir talk 17:45, 25 November 2017 (UTC)
No problem, Waldir! I hope they can get what they need out of there. :) Megalibrarygirl (talk) 18:25, 25 November 2017 (UTC)
Not sure what I'm supposed to do here, but the following section is the text of the article. If someone can transfer it into mainspace then the section can be reverted. 2A00:23C0:8601:9701:3066:7135:A200:564F (talk) 13:33, 30 November 2017 (UTC)
The below text on a "Revised Gregorian calendar" appears to be complete OR, originating from the banned user on [talk page]. Indeed, the text's placement in Megalibrarygirl's userspace could be an attempt to circumvent proper processes after Draft:Revised Gregorian calendar was deleted twice. If so, there is no point in keeping the page, nor is there any reason to move the text into mainspace. Arcorann (talk) 04:35, 22 January 2018 (UTC)
You haven't edited any talk page for a year and a half. The article has been cleared for transfer to mainspace by two administrators (one of whom said that he would have done the job himself if his native language had been English). Apart from the scrutiny it has received, the fact that the draft has six references is an indication that your claim that it "appears to be complete O[riginal] R[esearch]" is wholly misconceived. 2A00:23C0:8601:9701:15C7:C14B:DFF5:4509 (talk) 16:34, 24 January 2018 (UTC)

Revised Gregorian calendar[edit]

Because of tracking errors the frequency of centennial leap years will have to be reduced if the dates of the equinoxes and solstices are to be maintained. Tidal friction causes a progressive increase in the length of the day, the retardation in clock time compared to about 1820 being known as delta T.

If the present Gregorian calendar is left unaltered the dates of the equinoxes and solstices will continue to move backwards as they have done since it was first introduced in 1582. The calendar could be reconfigured so that the mean vernal equinox[1] never falls later than 1 PM Greenwich Mean Time on 19 March. The significance of this is that the astronomical equinox in turn falls no later than noon GMT on 21 March. This prevents Easter Sunday falling on the same day as the astronomical equinox anywhere in the world.

The trigger for the introduction of the Revised Gregorian calendar would be when the mean vernal equinox in a year giving remainder three on division by 400 was calculated to fall for the first time earlier than 1 PM (GMT) on 18 March. The preceding leap year would be cancelled. Thereafter all centennial years would normally be common, until the third year following was calculated to have a mean vernal equinox later than 1 PM (GMT) on 19 March, in which case the preceding leap year would be reinstated.

Extrapolating delta T forward, based on the average rate of increase over the past 27 centuries,[2][3][4] the tipping point will be reached in the year 8403, when the mean vernal equinox is calculated to fall at 3 AM (GMT) on 18 March,[5] conveniently very close to the year (AD 8599) when the Easter table in the Book of Common Prayer of the Church of England expires.[6] AD 8400 would be common, with the next two centennial leap years in AD 8800 and AD 9700. These dates are only provisional, since the future rate of increase of delta T cannot be predicted with complete certainty. Looking further ahead, when the mean tropical year drops below 365.24 days the minimum four-year interval between leap years will have to be extended.

Looking ahead millions of years, if there are still people around then, when the mean tropical year falls below 365 days, August would lose a day. Below 364 days, December would lose a day. Below 363 days, January would lose a day. Below 362 days, August would lose another day. Below 361 days, December would lose another day. Below 360 days, June would lose a day. Below 359 days, April would lose a day. Below 358 days, September would lose a day. Below 357 days, November would lose a day. Below 356 days, January would lose another day, thus restoring the lengths of the months to those of the Roman Republican calendar, which was replaced by the Julian, itself replaced by the Gregorian.


  1. ^ Olson, Donald W; Fienberg, Richard Tresch; Sinnott, Roger (27 July 2006). "What Is A Blue Moon?". Sky and Telescope. Retrieved 1 November 2017. 
  2. ^ Morrison, L V; Stephenson, F R (2004). "Historical Values of the Earth's Clock Error Delta T and the Calculation of Eclipses". Journal for the History of Astronomy. 35: 327–36. 
  3. ^ Stephenson, F R (2008). Historical eclipses and earth's rotation. Cambridge. 
  4. ^ Stephenson, F R (April 2003). "Historical eclipses and earth's rotation" (PDF). Astronomy and Geophysics. 44: 2.22–2.27. 
  5. ^ The calculations were made using SOLEX-11.
  6. ^ Church of England (1952). Book of Common Prayer:General tables for finding the Dominical or Sunday Letter, and the places of the Golden Numbers in the Calendar (PDF). Oxford. p. 38. 

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