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Is there any objection if I set up automatic archiving of old discussions? Jc3s5h ( talk) 14:45, 22 March 2015 (UTC)
What citation format would people prefer for this article? If it were left to me, I would use the {{ Citation}} format since most sources are only mentioned once or twice, so there is no need to set up short citations plus a bibliography. The first citation used APA style and was just an general reference, not an inline citation. Jc3s5h ( talk) 14:45, 22 March 2015 (UTC)
The first edit I can find that contains a word spelled differently in British and American English is here; it is from 2006. Based on this, I think the spelling in this article should be British. Comments? Jc3s5h ( talk) 15:13, 22 August 2015 (UTC)
British English with "-ize" spellings is so-called Oxford spelling... AnonMoos ( talk) 14:23, 26 August 2015 (UTC)
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The International Union of Pure and Applied Chemistry and the International Union of Geological Sciences have jointly recommended using approximately 365.24219265 ephemeris daits (day and night) as the length of the tropical year (in the year 2000). Since 1 year period is 0.24219265 daits longer than a whole number of daits, it takes 4 years (4 * 0. 24219265 = 0.96877060) to gain nearly a full dait. thus the calendar adds a leap dait every 4 years. Therefore, a 4 year period is now 0.03122940 daits shorter than a whole number of daits, and it takes 32 * 4 years (32 * 0.03122940 = 0.99934080) to lose nearly a full dait, thus the calendar subtracts a leap dait every 128 years. Finally, a 128 year period is now 0.00065920 daits longer than a whole number of daits, and it takes 1516 * 128 years (1516 * 0.00065920 = 0.99934720) to gain nearly a full dait, but the calendar ignores a leap dait error every 194048 years.
if (year is not exactly divisible by 4) then (it is a common year) So much easier, how about it? 4wikin9 ( talk) 12:07, 22 January 2016 (UTC) |
It is surprising the article doesn't simply start by pointing out that the tropical or solar year is around 365.2422 days long currently, thus to keep the calendar year aligned with it (so the seasons don't drift, etc.), one needs to add about a day every four years. If you want to get fancy, since .25 isn't quite the same as .2422 (or thereabouts), you can improve the correction by observing or not observing leap years at the years divisible by 100 or 400 as needed. Starting with the length of the tropical year (365.2421... days) makes the explanation of leap years a lot easier than the rather vague statement that this article starts with: "Because seasons and astronomical events do not repeat in a whole number of days, calendars that have the same number of days in each year drift over time with respect to the event that the year is supposed to track." — Preceding unsigned comment added by 192.158.48.16 ( talk) 12:07, 29 February 2016 (UTC)
Wikipedia is not a database of code, and I do not see why there needs to be pseudocode to figure out if year X is a leap year. "Some exceptions to this basic rule are required since the duration of a tropical year is slightly less than 365.25 days ... The Gregorian calendar therefore removes three leap days every 400 years, which is the length of its leap cycle. This is done by removing February 29 in the three century years (multiples of 100) that cannot be exactly divided by 400." is clear enough. Perhaps move it to Wikibooks for some programming tutorial, but it was indiscriminately placed. Esquivalience t 21:33, 29 February 2016 (UTC)
In
this edit, I just added a statement about how Neil deGrasse Tyson described this algorithm in words. Source video is posted in the reference.
What NdT did not address is how the calendar is driven by cycles of the Sun & Moon with the Earth's rotation & revolution. It is a "cosmic coincidence" that the Sun & Moon have the same apparent size to us. This is because the size-distance ratio of the Sun & Moon is 400. The Sun is 400 times the diameter of the Moon, and the Sun is 400 times the distance of the Moon. Result: Same apparent size.
If NdT had wanted to present more intriguing facts, he would have pointed out this further "cosmic coincidence" in the similarity to the Leap Year rule: 4 x 100 = 400.
There is a similar pattern in the relationship between the Sun-Moon-Earth in space as well as time.--
Tdadamemd sioz (
talk) 22:55, 29 February 2016 (UTC)
...and to give one more layer of connection, NdT could also have explained the similarity in the rotation period of the Sun with the orbit period of the Moon: both are 27 days.-- Tdadamemd sioz ( talk) 00:10, 1 March 2016 (UTC)
A year is or was a leap year if it is divisible by 4, except if both of the following apply:
All years that are not leap years are common years. For example, 1900 was not a leap year because although it is divisible by 4, it is also divisible by 100 and not by 400. 2000 was a leap year because although it is divisible by 100, it is also divisible by 400. This fails the requirement that both of the above conditions must be true in order for a year divisible by 4 to be a common year. |
Imparts more information in about the same length as the current section. Esquivalience t 00:52, 1 March 2016 (UTC)
The following paragraph was recently added to the lead of this article:
The same type of problem happens in the relationship between the day and the number of seconds in the day: If you divide the larger measure of time by the smaller, you do not get a whole number. Instead, the result is an unending decimal. There is no way to perfectly fit a whole number of seconds into a day, nor is there a way to perfectly fit a whole number of days/months into a year. As leap years are used to correct calendar drift, the resulting drift in measuring the diurnal cycle is corrected by the use of leap seconds.
Since there is no language further describing the meaning of this paragraph, it must understood in the context of this article, which is various calendars that have existed for the last few millennia. Leap seconds are not really comparable to leap days. In the calendars that use them, including the Gregorian calendar which is the world-wide standard for international commerce, everybody observes the leap day on the required day. For leap seconds, on the other hand, only a minuscule proportion of time keeping devices are even capable of representing a leap second; most people don't even worry about it and just treat it as one more source of error that gets corrected the next time their time-keeping device is reset.
Among those who do care about each and every second are astronomers. They have a wide variety of time scales to choose from, such as Coordinated Universal Time (UTC), UT1, Terrestrial Time, and International Atomic Time. Of these, only UTC observes leap seconds.
What about the law? Although the "official" time broadcasts or other "official" sources of time in virtually every country contain leap seconds, this has not been recognized by the law in the US until 2007 (see America COMPETES Act). The UK and Canada have still not passed laws to switch from mean solar time to UTC. (See http://www.publications.parliament.uk/pa/ld199798/ldhansrd/vo970611/text/70611-10.htm ).
These complexities are too much to cover in this article, so leap seconds should not be covered in this article. Jc3s5h ( talk) 23:41, 29 February 2016 (UTC)
Jc3s5h, this statement of yours needs a specific rebuttal:
You may not care about 1 second. But computers care. Airplanes care. Self-driving cars care. Navigation these days happens via speed of light signals. That's 300,000 kilometers-per-1-second. The previous section here is a discussion about computer algorithms. Code is likewise written to implement leap seconds. So you say you don't care, but if the website you're trying to access crashes because of poorly written code, you might start to care. And that's to say nothing of an airplane or car that you're riding in.-- Tdadamemd sioz ( talk) 04:19, 1 March 2016 (UTC)
To try to move things along, I propose the following replacement for the last paragraph in the lead.
-- Elphion ( talk) 17:52, 2 March 2016 (UTC)
The " Accuracy" section of the " Gregorian calendar" article discusses how well the Gregorian calendar achieves this design goal, and how well it approximates the tropical year.
OK, here's a revised proposal:
-- Elphion ( talk) 21:49, 3 March 2016 (UTC)
@ Jc3s5h: Clarify, please. Do you think that the first paragraph of the suggested text (or any reference to leap-seconds) is inappropriate for the lead? This is the obvious place to point interested readers to Leap second, even if we omit direct reference to the Gregorian calendar. -- Elphion ( talk) 17:06, 11 March 2016 (UTC)
if ((year is divisible by 400) or ((year is divisible by 4) and (year is not divisible by 100))) then (leap year)
else (common year)
in C:
bool isLeapYear(int year)
{
return year % 400 == 0 || year % 4 == 0 && year % 100 != 0;
}
— Preceding unsigned comment added by 77.239.254.82 ( talk) 20:32, 3 September 2015
In the version in the article, surely if "year" is not exactly divisible by 100 it won't be divisible by 400 either, so the third "if" will never be satisfied? MarkGeater ( talk) 03:43, 30 October 2015 (UTC)
Then just move the 400 test to the end.
bool isLeapYear(int year)
{
return year % 4 == 0 && year % 100 != 0 || year % 400 == 0;
}
87.102.44.18 ( talk) 12:05, 6 March 2016 (UTC)
In C#:
// Gregorian.isLeapYear(year) will return TRUE for any year in the set { 0 < year < 3200 }
// Calculations: (year % 100) > 0 — if the year is not a century (year % 4) will equal 0 only for leap years
// otherwise: (year % 400) — evaluates to a non-zero value for all years not divisible by 400
// Derives a Boolean result using only one conditional/test, one comparison and two calculations.
public class Gregorian
{
public static bool isLeapYear(int year) { return (year % ((year % 100)>0 ? 4 : 400)) == 0; }
}
— 216.240.6.210 ( talk) 01:51, 20 March 2016 (EDT)
"Most efficient" leap year test:
This code is valid in C, C++, C#, Java, and many other C-like languages. This "most efficient" code below replaces costly modulo (division) operations with bit-wise logical AND operations, and terminates after only ONE operation for three-quarters of all cases. The costly division (modulo 25) for the 100th year test only executes for "4th year" cases:
// Most efficient leap year test
// See: http://stackoverflow.com/questions/3220163/how-to-find-leap-year-programatically-in-c/11595914#11595914
if ((year & 3) == 0 && ((year % 25) != 0 || (year & 15) == 0))
{
/* leap year */
}
— Kriceslo ( Kriceslo) 12:29, 23 November 2016 (UTC)
if (year is divisible by 400) then (it is a leap year) else if (year is divisible by 100) then (it is a common year) else if (year is divisible by 4) then (it is a leap year) else (it is a common year)
What both of the previous suggestions overlook is the arrangement of the tests to handle the most frequent cases first for efficiency. The second proposal is in fact just the reverse of the algorithm in the article, so hardly any more or less difficult to understand. -- Elphion ( talk) 04:00, 7 March 2016 (UTC)
Certainly there must be a traditional term for a common year's missing (or lack of) a Leap Year Eve.
Dlf1wayout ( talk) 07:56, 28 February 2017 (UTC) Dlf1wayout a.k.a. LSDexitOzAmericaDotOrg
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Pls include "List of leap years (till 3004)" article at "See also" section. Thanks 86.59.211.222 ( talk) 02:08, 20 June 2017 (UTC)
The leap algorithm only applies to 1752 and onwards.
This means 1700 has 366 days even though by definition it is not a leap year.
Check it for your self. I propose editing the main article to reflect this. — Preceding unsigned comment added by 110.174.28.45 ( talk) 01:59, 18 March 2018 (UTC)
This wiki article says "For example, the years 1700, 1800, and 1900 were not leap years, but the years 1600 and 2000 were." And if you check the year 1700 has 366 days (i.e. has Feb 29). So the algorithm fails for 1700. But from 1800 it is correct. Since 1752 was the year that Gregorian Calendar was adopted by the British Empire, this means the algorithm only applies to 1752 onwards. Hence this wiki article is not fully correct. If you look around the internet you will see the same "misinformation". I think we should try to make it a bit more correct. — Preceding unsigned comment added by 110.174.28.45 ( talk) 06:18, 18 March 2018 (UTC)
Okay, so after some more thoughts, here are my conclusions:
See the following example:
Year | Leap or Not Leap according to Algorithm | Number of days inferred from leap or not leap | Actual number of days in the year |
---|---|---|---|
1300 | Not Leap | 365 | 366 |
1400 | Not Leap | 365 | 366 |
1500 | Not Leap | 365 | 366 |
1600 | Leap | 366 | 366 |
1700 | Not Leap | 365 | 366 |
1800 | Not Leap | 365 | 365 |
1900 | Not Leap | 365 | 365 |
2000 | Leap | 366 | 366 |
From that perspective, we could say algorithm result for all years >1700 (not including 1700) can be used to infer number of days in the year.
-- 110.174.28.45 ( talk) 11:09, 18 March 2018 (UTC)
I'm not necessarily suggesting this should be added because it's not currently recognized as necessary (and it won't be necessary for over 1000 years), but in order to keep the progression of leap/common year accurate over time, the algorithm would have to be extended as follows:
if (year is not divisible by 4) then (it is a common year)
else
if (year is not divisible by 100) then (it is a leap year)
else
if (year is not divisible by 400) then (it is a common year)
else
if (year is not divisible by 3200) then (it is a leap year)
else (it is a common year)
In other words, even though the year 3200 is divisible by 400, it will have to be a common year to keep the calendar accurate. The next steps in this progression (obviously not necessary to worry about any time soon) would be the year 86,400 (a leap year even though divisible by 3200) and the year 13,478,400 (a common year even though divisible by 86,400). - Embram ( talk) 08:56, 8 December 2014 (UTC)
The algorithm as it is is a bit ugly to read. Being explicit on the logical condition might be quicker to understand. if ( year divisible by 4 and year not divisible by 100) or year divisible by 400) then leap year else normal year 191.115.28.196 ( talk) —Preceding undated comment added 21:27, 25 September 2015 (UTC)
function isLeapYear(year) {
return year is divisible by 4
&& (year is not divisible by 100 || year is divisible by 400)
}
Every leap year is every 4th year. To not overcomplicate things when using just the regular date and calendar, all you need to do is to check if the modulo 4 of year = 0, you can do this simply by checking:
C++ / Java: leapyear = year % 4; if (leapyear == 0) { // we got leapyear}
Visual Basic: leapyear = year mod 4: if (leapyear = 0) then ' we got leapyear
// isLeapYear will be TRUE if the value of "year" represents a leap year:
bool isLeapYear = (year % ((year % 100)>0 ? 4 : 400)) == 0;
// Perhaps, most succinct, but NOT most efficient because 100th year test is performed every time
bool isLeapYear = (year & (year % 25 != 0 ? 3 : 15)) == 0;
// Most efficient leap year test
// See: http://stackoverflow.com/questions/3220163/how-to-find-leap-year-programatically-in-c/11595914#11595914
bool isLeapYear = (year & 3) == 0 && (year % 25 != 0 || (year & 15) == 0);
— Preceding unsigned comment added by 37.196.158.254 ( talk) 01:14, 11 January 2016 (UTC)
This edit by [User:156.61.250.250]] asserts "Averaged over the long term, the vernal equinox year is equal to the mean tropical year, which is the same as the time between successive mean vernal equinoxes." But as our article Tropical year and the numerous sources cited in that article make clear, a mean tropical year is not the same as the time between successive mean vernal equinoxes (if indeed the term "mean vernal equinoxes" is even defined by the astronomical community. One highly authoritative source, the The Astronomical Almanac Online! (Glossary) does not define "mean tropical year" but defines "year, tropical" as
the period of time for the ecliptic longitude of the Sun to increase 360 degrees. Since the Sun's ecliptic longitude is measure with respect to the equinox, the tropical year comprises a complete cycle of seasons, and its length is approximated in the long term by the civil (Gregorian) calendar. The mean tropical year is approximately 365 days, 5 hours, 48 minutes, 45 seconds.
This is clearly different from "time between successive mean vernal equinoxes."
Even if some plausible explanation could be contrived to show the statement is true for some interpretation of "mean" and some interpretation of "averaged over the long term" it is not helpful to include a claim that is not supported by a reliable source and uses language differently from how it is used by the astronomical community. Jc3s5h ( talk) 14:47, 2 March 2015 (UTC)
mean equinox and equator: the celestial reference system determined by ignoring small variations of short period in the motions of the celestial equator and ecliptic. Thus the mean equinox and equator are affected only by precession. Positions in star catalogs are normally referred to the mean catalog equinox and equator of the beginning of a Besselian year.
The problem with terms like "vernal equinox year" and "(mean) time interval between two successive spring equinoxes" is that these terms are not defined. This is an encyclopaedia, and our mission is to define terms for the benefit of our readers. 156.61.250.250 ( talk) 11:44, 7 March 2015 (UTC)
P.S. See
File:CompareTropicalYears.png for a visual graph...
AnonMoos (
talk) 16:11, 19 July 2015 (UTC)
For a more thorough discussion of tropical, equinoctial and solstitial years see The Lengths of the Seasons (on Earth) by Dr. Irv Bromberg of the University of Toronto. He gives their lengths in terms of the number of mean solar days increasing in length at an average rate of 1.75 ms/century as well as atomic days of 86,400 SI seconds per day. He presents their sinusoids using many multicolored graphs up to ±100,000 years, some with the mean lengths of various calendars. He used numerical integration via SOLEX designed by Professor Aldo Vitagliano of the University of Naples, in contrast to the polynomials used by Jean Meeus valid for only a limited period of time. Although Meeus discusses the lengthening mean solar day, his tabulations and graph of the lengths of the various years use ephemeris days, identical to atomic days. — Joe Kress ( talk) 21:48, 2 January 2019 (UTC)
The following discussion is closed. Please do not modify it. Subsequent comments should be made on the appropriate discussion page. No further edits should be made to this discussion.
Should the phrase "peer-reviewed" be used in connection with stackoverflow in a way that suggests stackoverflow.com contributions are peer reviewed? In particular see this recent edit. Jc3s5h ( talk) 22:44, 9 December 2018 (UTC)
(Comment by author of edit in question: Not every contribution to Stack Overflow is purported to be "peer-reviewed". At issue, is Verifiability and Reliability: "Base articles on reliable, third-party, published sources with a reputation for fact-checking and accuracy." Stack Overflow CAN BE such a source. Over many years, heavily up-voted and moderator-scrunitized contributions to Stack Overflow certainly do gain legitimate peer-review. From Peer review: "Peer review requires a community of experts in a given (and often narrowly defined) field, who are qualified and able to perform reasonably impartial review." Stack Overflow is such a community of experts and its voting and moderation scheme ensures the highest-quality contributions are vetted. Rigorous Scholarly peer review should not be confused with or cited as a tool to detract from legitimate, "Verifiable" and "Reliable" peer-reviewed sources.) — Kriceslo ( talk) 10:04, 10 December 2018 (UTC)
There is no consensus to remove the pseudocode in the "Algorithm" section or replace it with code from a programming language. The consensus is that English is more broadly understood by readers than code and that code would require an explanation in English which would add unnecessary duplication to the article. Some editors recommended adding external links that contain code for the leap year algorithm.
Should Leap Year page include a computer programming example on how to calculate leap years? The Leap Year page is cited by numerous computer programmers [6] [7] and is used as a reference by programmers for information on how to calculate whether a given year is a Leap Year. Editors of the Leap Year page argue WP:NOTHOWTO (but nevertheless provide a textual algorithm). However, WP:BB argues that providing a real programming example in the very place that is turned to by many programmers makes the encyclopedia better ( WP:FATRAT). A single one-line programming example (in the vastly common C programming language) is proposed. — Kriceslo ( talk) 09:38, 10 December 2018 (UTC)
I have deleted the Hindu calendar section, mostly because it was unreferenced. Nachum Dershowitz and Edward Reingold in their book Calendrical Calculations 3rd ed. (Cambridge University Press, 2008) include two relevant chapters: chapter 9, "Old Hindu Calendars", and chapter 18, "Modern Hindu Calendars". The later chapter on p. 275 indicates there are over 30 variations of the Hindu calendar in active use.
This section should not be restored until a knowledgeable person with access to appropriate reliable sources to cite can create a version that accounts for all the different versions, discuss their relative popularity, and describe the leap month for one or more of the popular versions. -- 13:56, 9 May 2019 Jc3s5h
Wouldn't it be a good idea to somewhere in this article to give a list of the historical leap years in Julian Calendar?
As far as I know, the list goes something like this: 45 BC, 42 BC (*), 39 BC, 36 BC, 33 BC, 30 BC, 27 BC, 24 BC, 21 BC, 18 BC, 15 BC, 12 BC, 9 BC, AD 8 (**), AD 12, ...
(*) Julius Caesar decreed a leap year every 4 years but he was assassinated and the people who took over administration of the calendar screwed up and made a leap year every 3 years instead. When Augustus took over he declared no leap years between year 8 BC and 8 AD.
(**) I am unsure if year AD 8 was a leap year or not, but it is certain that year 12 and every 4 year after 12 was a leap year until Gregorian calendar took over. I am also certain that year 5 BC, 1 BC and AD 4 was all common years and not leap years. — Preceding unsigned comment added by AlfSalte ( talk • contribs) 07:25, 4 July 2020 (UTC)
In the conversation at the beginning talking about the reason for the leap day and the calculation for them, should there be a mention of why all of this is needed? There is a mention in the first section, Gregorian Calendar, showing the calculation of leap years resulting in 365.2425 days. I've read in several places (although do not have a definitive source) that the actual astronomical year is approximately 365.23 days. If someone can find a reference to this, should it be added to the header discussion to reinforce the reason for leap years? 19:27, 12 December 2019 (UTC) -- Preceding unsigned comment added by 198.70.201.220 ( talk)
User:John_Maynard_Friedman -- It's obvious from the structure of Kalends, Nones, and Ides etc, that a remote ancestor of the Roman Calendar as we know it must have been originally lunar. However, the immediately previous Roman calendar, which Julius Caesar changed in 45 B.C. was neither "Lunar" nor "Lunisolar". It was a rather odd entity where months no longer kept in phase with the moon, but the basic year length wasn't close to 365 days either. Every few years, a 13th month (sometimes called "Mercedonius") was inserted after February 23rd or 24th to keep the calendar in sync with the sun -- but the priests who were in charge of the intercalation were often incompetent and/or more concerned with shortening the terms in office of their enemies, or lengthening the terms in office of their friends, than in astronomy, so it had a tendency to drift out of sync with the tropical year. In 190 B.C. there was a solar eclipse which took place on July 11th of the Roman calendar as it then existed, but the date is March 14th according to modern calculations, so that the calendar was already pretty messed up (and probably no longer lunar) even back then... For more than you could possibly want to know about the pre-45 B.C. Roman calendar, see the book The Calendar of the Roman Republic by Agnes Kirsopp Michels... AnonMoos ( talk) 16:21, 8 December 2020 (UTC)
AnonMoos, when you wrote "(rather than one which was either strictly lunar or strictly solar)", did you intend to write "(rather than one which was neither strictly lunar or strictly solar)" ? -- John Maynard Friedman ( talk) 19:49, 8 December 2020 (UTC)
The intro section in #Julian calendar has been changed so often that it no longer reads sensibly. I don't have access to Cheney's A Handbook of Dates for students of British History but I suspect it is clearer than our current "The Romans treated leap day as a second sixth day before the Kalends (first day) of March, in Latin ante diem bis sextum Kalendas Martias." Should this read "The Romans treated leap day as a second sixth day in the week before the Kalends (first day) of March"? Even if it did, I can't see how that would have the effect of doubling 24 February. Would someone clarify, please? --
John Maynard Friedman (
talk) 07:49, 20 April 2021 (UTC)
Because the Romans used ' inclusive counting', "the sixth day before the Kalends of March" is reckoned by counting backwards from – and including – the first of March. February had an invariable 28 days (the leap day not being counted), so 28 February was the second day 'before' the Kalends and thus 24 February was the sixth day.
I find that the leap year algorithm can be clearer if rephrased as
if (year is
divisible by 400) then (it is a leap year)
else if (year is divisible by 100) then (it is a common year)
else if (year is divisible by 4) then (it is a leap year)
else (it is a common year)
instead of
if (year is not
divisible by 4) then (it is a common year)
else if (year is not divisible by 100) then (it is a leap year)
else if (year is not divisible by 400) then (it is a common year)
else (it is a leap year)
-- 201.229.5.234 ( talk) 12:35, 4 June 2021 (UTC)
An editor has identified a potential problem with the redirect List of leap years and has thus listed it for discussion. This discussion will occur at Wikipedia:Redirects for discussion/Log/2022 March 10#List of leap years until a consensus is reached, and readers of this page are welcome to contribute to the discussion. GeoffreyT2000 ( talk) 18:19, 10 March 2022 (UTC)
I am not particularly a fan of this graph:
I'm sure it's accurate enough, but it seems to have some presentation issues. Setting aside that it renders too wide and blows out the page width of the article, the (IMHO far greater) sin it commits is displaying a Y axis populated with dates like "June 20.5", "June 21.5", and "June 22.5". That's not a real thing.
The file is SVG, so in theory those issues could be corrected by hand-editing the graph. It isn't immediately obvious how one would go about actually regenerating the graph, though, since I've downloaded the software that purportedly supplied the data and I can't find any options for getting such a graph out of it. Unless perhaps the original uploader pulled the data points out of the source code, and graphed them some other way. FeRDNYC ( talk) 00:57, 18 October 2022 (UTC)
It is interesting that until the start of the year was moved from March 25 to January 1, no leap year actually contained a leap day. For example, the leap day for 1604 was Feb 29 1603. 2600:4040:5D30:4800:6416:83BB:F540:FFC9 ( talk) 14:53, 16 December 2022 (UTC)
References
The current text describes the 24 February bissextile day, then jumps to only the churches continuing to use it. We have nothing on when and where the practice changed? Anyone? 𝕁𝕄𝔽 ( talk) 16:42, 19 December 2022 (UTC)
Found it! (well, -ish).
Etymologically it is the double sixth day before the Calends of March, i.e. 24-25 February. But in spite of Edward I's ordinance and Seymour's meticulous observance thereof as late as 1552, it is clear that the bi-sextile day had in common use lost its etymological meaning. It might even seem that in fourteenth and fifteenth centuries, having cast loose from etymological moorings, it drifted up and down through February and even occasionally into January. As early as 1352 we find a chancery clerk dating an item on the close roll '29 February' yet exactly two centuries later Seymour adorns his Commons journal with precise repetition of the Roman style. In interval we find on the patent, close, or 'fine' rolls 29 February 1376, 1380, 1401, 1404, 1406, 1408, 1472 (thrice), 1481, a 1484 (twice); and it looks as though the bi-sextile day was settling down on its unetymological date of pridie Kal. Marti. But the fact that we find it in 1401 and 1406 as well as in 1404 and in 1481 as well as in 1484, not to mention Seymour's classical reaction, indicates a good deal of chronological hesitation. This is confirmed by still stranger aberrations: in 1393 we had '30 February', and again three times in 1484 (in addition to 29 February), and once in 1508 without a 29 February. Even more extraordinary are the '33 February' in 1493, the '32 January' in 1388, and the '33 January' in 1473." In 1512 we have a '29 February for leap year, but later in Henry VIII reign there is a distinct but natural tendency to take refuge in the ambiguous ultimo. How far Seymour's reaction was representative I do not know; but in the whole of the patent rolls, from Edward VI's accession down to the end (1560) of the latest published volume of the calendar, I have not found single 29 February. Many of the patents are undated and some omit either the day of the month or the month itself; but the only positive anomalies I have noted are the '31' November 1547 and a patent dated 25 December.
— A F Pollard "New Year's Day and Leap Year in English History" (p. 187) The English Historical Review Vol. 55, No. 218 (Apr., 1940), pp. 177-193 (17 pages) https://www.jstor.org/stable/553864
So, like a number of writers I found, I think we have to hide behind the vague "middle ages"? Although "about the fifteenth century" doesn't seem unreasonable if we cite Pollard? Comments? -- 𝕁𝕄𝔽 ( talk) 21:20, 20 December 2022 (UTC)
[I also recommend Google Lens I don't fancy my chances of transcribing those extracts correctly.] -- 𝕁𝕄𝔽 ( talk) 01:07, 22 December 2022 (UTC)However that may have been, the bi-sextile day was the sixth day, counted backwards according to the Roman system, from 1 March; it fell on 24 February, which was counted twice. But there were obvious disadvantages in having two days of the week on one day of the month, though no doubt it produced the well-known surname of Doubleday; and the Romans adopted the practice of differentiating the two by calling 24 February the 'posterior' bi-sextile day, and the 25th the 'prior' bi-sextile day, the 24th being behind, in their backward reckoning, the 25th day. This Roman practice was meticulously followed by John Seymour, the clerk of the commons in February 1552 when, after the heading Mercurii, 24° Februarii' in his journal, he has 'Jovis, quoque 24° pr' dies bisext."
POSTSCRIPT: Cheney (2000) [1945] (p. 8) is more explicit:
Christian festivals in a leap year
An anomaly arising from the Church’s adoption of the Roman calendar requires brief consideration. Using the Roman calendar, The Intercalary Day (bis VI Kal. Mart.) preceded the common VI Kal. Mart. When the simple numbering of days was adopted, the intercalary day appeared to be 29 February, but canonically it was 24 February, the exact equivalent of bis VI Kal. Mart. In leap years, therefore, St Mathias was commemorated on 25 February rather than 24 February, which was counted as Vigilia S. Matthei apostoli. This came to be regarded as a popish custom in England, and in the 1680s St Mathias came to be kept on 24 February, and the saints of the remaining days of February were not postponed; 29 February became de facto the intercalary day.
I will see how best to integrate that, since it is quite emphatic and Cheney is the RS (though I prefer Pollard's cockup theory and he cites his sources). -- 𝕁𝕄𝔽 ( talk) 16:58, 27 December 2022 (UTC)
The series of edits made by John Maynard Friedman on December 21, 2022, seems to conflate two potentially distinct changes. The first change was going from the idea of a double-day with a single date to two days with distinct dates. Before the change, in a leap year, February 24 lasted 48 hours and February contained 28 days. The second change, which might have occurred at the same time as the first change, or later, is to consider the intercalary day to be February 29 rather than February 24.
The mere fact that a calendar shows 29 days for February does not necessarily mean that February 29 was the intercalary day. As the movement of the [f]east of Saint Matthias shows, February 24 could still be considered the intercalary day even with a calendar that shows a February 29. If the drinking law recognized the first change but not the second, I suppose a US person born February 27, 2003 would have to wait until February 28, 2024 to buy a drink in a bar. Jc3s5h ( talk) 21:47, 21 December 2022 (UTC) Fixed typos pointed out by JMF at 01:23 December 22, 2021 UTC.
———
But in spite of Edward I's ordinance and Seymour's meticulous observance thereof as late as 1552, it is clear that the bi-sextile day had in common usage lost its etymological meaning. It might even seem that in the fourteenth and fifteenth centuries, having cast loose from its etymological moorings, it drifted up and down through February, and even occasionally into January.
In 1551/2 the new clerk of the lords also ignores the etymological bi-sextile day and has Tuesday 23, Wednesday 24, Thursday 25, Friday 26, and Saturday 27 February. He has then an adjournment to Thursday, 3 March. So, unlike his colleague in the Commons, he abstains from a bi-sextile 24 February, while an adjournment makes it doubtful whether he visualized a 29 February or a 'bi-sextile' 1 March like his predecessor in 1543/4.
The O.E.D. describes the word 'bis-sextile' as 'obsolete', and we may conclude that it became so during the latter half of the sixteenth century, the process having taken at least two hundred years since a chancery clerk dated a document '29 February' in 1351/2.
I have begun to rework the section to take into account this discussion. It will take a few days as I don't have a lot of free time just now. -- 𝕁𝕄𝔽 ( talk) 08:28, 27 December 2022 (UTC)
This is an archive of past discussions. Do not edit the contents of this page. If you wish to start a new discussion or revive an old one, please do so on the current talk page. |
Archive 1 | Archive 2 | Archive 3 |
Is there any objection if I set up automatic archiving of old discussions? Jc3s5h ( talk) 14:45, 22 March 2015 (UTC)
What citation format would people prefer for this article? If it were left to me, I would use the {{ Citation}} format since most sources are only mentioned once or twice, so there is no need to set up short citations plus a bibliography. The first citation used APA style and was just an general reference, not an inline citation. Jc3s5h ( talk) 14:45, 22 March 2015 (UTC)
The first edit I can find that contains a word spelled differently in British and American English is here; it is from 2006. Based on this, I think the spelling in this article should be British. Comments? Jc3s5h ( talk) 15:13, 22 August 2015 (UTC)
British English with "-ize" spellings is so-called Oxford spelling... AnonMoos ( talk) 14:23, 26 August 2015 (UTC)
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The International Union of Pure and Applied Chemistry and the International Union of Geological Sciences have jointly recommended using approximately 365.24219265 ephemeris daits (day and night) as the length of the tropical year (in the year 2000). Since 1 year period is 0.24219265 daits longer than a whole number of daits, it takes 4 years (4 * 0. 24219265 = 0.96877060) to gain nearly a full dait. thus the calendar adds a leap dait every 4 years. Therefore, a 4 year period is now 0.03122940 daits shorter than a whole number of daits, and it takes 32 * 4 years (32 * 0.03122940 = 0.99934080) to lose nearly a full dait, thus the calendar subtracts a leap dait every 128 years. Finally, a 128 year period is now 0.00065920 daits longer than a whole number of daits, and it takes 1516 * 128 years (1516 * 0.00065920 = 0.99934720) to gain nearly a full dait, but the calendar ignores a leap dait error every 194048 years.
if (year is not exactly divisible by 4) then (it is a common year) So much easier, how about it? 4wikin9 ( talk) 12:07, 22 January 2016 (UTC) |
It is surprising the article doesn't simply start by pointing out that the tropical or solar year is around 365.2422 days long currently, thus to keep the calendar year aligned with it (so the seasons don't drift, etc.), one needs to add about a day every four years. If you want to get fancy, since .25 isn't quite the same as .2422 (or thereabouts), you can improve the correction by observing or not observing leap years at the years divisible by 100 or 400 as needed. Starting with the length of the tropical year (365.2421... days) makes the explanation of leap years a lot easier than the rather vague statement that this article starts with: "Because seasons and astronomical events do not repeat in a whole number of days, calendars that have the same number of days in each year drift over time with respect to the event that the year is supposed to track." — Preceding unsigned comment added by 192.158.48.16 ( talk) 12:07, 29 February 2016 (UTC)
Wikipedia is not a database of code, and I do not see why there needs to be pseudocode to figure out if year X is a leap year. "Some exceptions to this basic rule are required since the duration of a tropical year is slightly less than 365.25 days ... The Gregorian calendar therefore removes three leap days every 400 years, which is the length of its leap cycle. This is done by removing February 29 in the three century years (multiples of 100) that cannot be exactly divided by 400." is clear enough. Perhaps move it to Wikibooks for some programming tutorial, but it was indiscriminately placed. Esquivalience t 21:33, 29 February 2016 (UTC)
In
this edit, I just added a statement about how Neil deGrasse Tyson described this algorithm in words. Source video is posted in the reference.
What NdT did not address is how the calendar is driven by cycles of the Sun & Moon with the Earth's rotation & revolution. It is a "cosmic coincidence" that the Sun & Moon have the same apparent size to us. This is because the size-distance ratio of the Sun & Moon is 400. The Sun is 400 times the diameter of the Moon, and the Sun is 400 times the distance of the Moon. Result: Same apparent size.
If NdT had wanted to present more intriguing facts, he would have pointed out this further "cosmic coincidence" in the similarity to the Leap Year rule: 4 x 100 = 400.
There is a similar pattern in the relationship between the Sun-Moon-Earth in space as well as time.--
Tdadamemd sioz (
talk) 22:55, 29 February 2016 (UTC)
...and to give one more layer of connection, NdT could also have explained the similarity in the rotation period of the Sun with the orbit period of the Moon: both are 27 days.-- Tdadamemd sioz ( talk) 00:10, 1 March 2016 (UTC)
A year is or was a leap year if it is divisible by 4, except if both of the following apply:
All years that are not leap years are common years. For example, 1900 was not a leap year because although it is divisible by 4, it is also divisible by 100 and not by 400. 2000 was a leap year because although it is divisible by 100, it is also divisible by 400. This fails the requirement that both of the above conditions must be true in order for a year divisible by 4 to be a common year. |
Imparts more information in about the same length as the current section. Esquivalience t 00:52, 1 March 2016 (UTC)
The following paragraph was recently added to the lead of this article:
The same type of problem happens in the relationship between the day and the number of seconds in the day: If you divide the larger measure of time by the smaller, you do not get a whole number. Instead, the result is an unending decimal. There is no way to perfectly fit a whole number of seconds into a day, nor is there a way to perfectly fit a whole number of days/months into a year. As leap years are used to correct calendar drift, the resulting drift in measuring the diurnal cycle is corrected by the use of leap seconds.
Since there is no language further describing the meaning of this paragraph, it must understood in the context of this article, which is various calendars that have existed for the last few millennia. Leap seconds are not really comparable to leap days. In the calendars that use them, including the Gregorian calendar which is the world-wide standard for international commerce, everybody observes the leap day on the required day. For leap seconds, on the other hand, only a minuscule proportion of time keeping devices are even capable of representing a leap second; most people don't even worry about it and just treat it as one more source of error that gets corrected the next time their time-keeping device is reset.
Among those who do care about each and every second are astronomers. They have a wide variety of time scales to choose from, such as Coordinated Universal Time (UTC), UT1, Terrestrial Time, and International Atomic Time. Of these, only UTC observes leap seconds.
What about the law? Although the "official" time broadcasts or other "official" sources of time in virtually every country contain leap seconds, this has not been recognized by the law in the US until 2007 (see America COMPETES Act). The UK and Canada have still not passed laws to switch from mean solar time to UTC. (See http://www.publications.parliament.uk/pa/ld199798/ldhansrd/vo970611/text/70611-10.htm ).
These complexities are too much to cover in this article, so leap seconds should not be covered in this article. Jc3s5h ( talk) 23:41, 29 February 2016 (UTC)
Jc3s5h, this statement of yours needs a specific rebuttal:
You may not care about 1 second. But computers care. Airplanes care. Self-driving cars care. Navigation these days happens via speed of light signals. That's 300,000 kilometers-per-1-second. The previous section here is a discussion about computer algorithms. Code is likewise written to implement leap seconds. So you say you don't care, but if the website you're trying to access crashes because of poorly written code, you might start to care. And that's to say nothing of an airplane or car that you're riding in.-- Tdadamemd sioz ( talk) 04:19, 1 March 2016 (UTC)
To try to move things along, I propose the following replacement for the last paragraph in the lead.
-- Elphion ( talk) 17:52, 2 March 2016 (UTC)
The " Accuracy" section of the " Gregorian calendar" article discusses how well the Gregorian calendar achieves this design goal, and how well it approximates the tropical year.
OK, here's a revised proposal:
-- Elphion ( talk) 21:49, 3 March 2016 (UTC)
@ Jc3s5h: Clarify, please. Do you think that the first paragraph of the suggested text (or any reference to leap-seconds) is inappropriate for the lead? This is the obvious place to point interested readers to Leap second, even if we omit direct reference to the Gregorian calendar. -- Elphion ( talk) 17:06, 11 March 2016 (UTC)
if ((year is divisible by 400) or ((year is divisible by 4) and (year is not divisible by 100))) then (leap year)
else (common year)
in C:
bool isLeapYear(int year)
{
return year % 400 == 0 || year % 4 == 0 && year % 100 != 0;
}
— Preceding unsigned comment added by 77.239.254.82 ( talk) 20:32, 3 September 2015
In the version in the article, surely if "year" is not exactly divisible by 100 it won't be divisible by 400 either, so the third "if" will never be satisfied? MarkGeater ( talk) 03:43, 30 October 2015 (UTC)
Then just move the 400 test to the end.
bool isLeapYear(int year)
{
return year % 4 == 0 && year % 100 != 0 || year % 400 == 0;
}
87.102.44.18 ( talk) 12:05, 6 March 2016 (UTC)
In C#:
// Gregorian.isLeapYear(year) will return TRUE for any year in the set { 0 < year < 3200 }
// Calculations: (year % 100) > 0 — if the year is not a century (year % 4) will equal 0 only for leap years
// otherwise: (year % 400) — evaluates to a non-zero value for all years not divisible by 400
// Derives a Boolean result using only one conditional/test, one comparison and two calculations.
public class Gregorian
{
public static bool isLeapYear(int year) { return (year % ((year % 100)>0 ? 4 : 400)) == 0; }
}
— 216.240.6.210 ( talk) 01:51, 20 March 2016 (EDT)
"Most efficient" leap year test:
This code is valid in C, C++, C#, Java, and many other C-like languages. This "most efficient" code below replaces costly modulo (division) operations with bit-wise logical AND operations, and terminates after only ONE operation for three-quarters of all cases. The costly division (modulo 25) for the 100th year test only executes for "4th year" cases:
// Most efficient leap year test
// See: http://stackoverflow.com/questions/3220163/how-to-find-leap-year-programatically-in-c/11595914#11595914
if ((year & 3) == 0 && ((year % 25) != 0 || (year & 15) == 0))
{
/* leap year */
}
— Kriceslo ( Kriceslo) 12:29, 23 November 2016 (UTC)
if (year is divisible by 400) then (it is a leap year) else if (year is divisible by 100) then (it is a common year) else if (year is divisible by 4) then (it is a leap year) else (it is a common year)
What both of the previous suggestions overlook is the arrangement of the tests to handle the most frequent cases first for efficiency. The second proposal is in fact just the reverse of the algorithm in the article, so hardly any more or less difficult to understand. -- Elphion ( talk) 04:00, 7 March 2016 (UTC)
Certainly there must be a traditional term for a common year's missing (or lack of) a Leap Year Eve.
Dlf1wayout ( talk) 07:56, 28 February 2017 (UTC) Dlf1wayout a.k.a. LSDexitOzAmericaDotOrg
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Pls include "List of leap years (till 3004)" article at "See also" section. Thanks 86.59.211.222 ( talk) 02:08, 20 June 2017 (UTC)
The leap algorithm only applies to 1752 and onwards.
This means 1700 has 366 days even though by definition it is not a leap year.
Check it for your self. I propose editing the main article to reflect this. — Preceding unsigned comment added by 110.174.28.45 ( talk) 01:59, 18 March 2018 (UTC)
This wiki article says "For example, the years 1700, 1800, and 1900 were not leap years, but the years 1600 and 2000 were." And if you check the year 1700 has 366 days (i.e. has Feb 29). So the algorithm fails for 1700. But from 1800 it is correct. Since 1752 was the year that Gregorian Calendar was adopted by the British Empire, this means the algorithm only applies to 1752 onwards. Hence this wiki article is not fully correct. If you look around the internet you will see the same "misinformation". I think we should try to make it a bit more correct. — Preceding unsigned comment added by 110.174.28.45 ( talk) 06:18, 18 March 2018 (UTC)
Okay, so after some more thoughts, here are my conclusions:
See the following example:
Year | Leap or Not Leap according to Algorithm | Number of days inferred from leap or not leap | Actual number of days in the year |
---|---|---|---|
1300 | Not Leap | 365 | 366 |
1400 | Not Leap | 365 | 366 |
1500 | Not Leap | 365 | 366 |
1600 | Leap | 366 | 366 |
1700 | Not Leap | 365 | 366 |
1800 | Not Leap | 365 | 365 |
1900 | Not Leap | 365 | 365 |
2000 | Leap | 366 | 366 |
From that perspective, we could say algorithm result for all years >1700 (not including 1700) can be used to infer number of days in the year.
-- 110.174.28.45 ( talk) 11:09, 18 March 2018 (UTC)
I'm not necessarily suggesting this should be added because it's not currently recognized as necessary (and it won't be necessary for over 1000 years), but in order to keep the progression of leap/common year accurate over time, the algorithm would have to be extended as follows:
if (year is not divisible by 4) then (it is a common year)
else
if (year is not divisible by 100) then (it is a leap year)
else
if (year is not divisible by 400) then (it is a common year)
else
if (year is not divisible by 3200) then (it is a leap year)
else (it is a common year)
In other words, even though the year 3200 is divisible by 400, it will have to be a common year to keep the calendar accurate. The next steps in this progression (obviously not necessary to worry about any time soon) would be the year 86,400 (a leap year even though divisible by 3200) and the year 13,478,400 (a common year even though divisible by 86,400). - Embram ( talk) 08:56, 8 December 2014 (UTC)
The algorithm as it is is a bit ugly to read. Being explicit on the logical condition might be quicker to understand. if ( year divisible by 4 and year not divisible by 100) or year divisible by 400) then leap year else normal year 191.115.28.196 ( talk) —Preceding undated comment added 21:27, 25 September 2015 (UTC)
function isLeapYear(year) {
return year is divisible by 4
&& (year is not divisible by 100 || year is divisible by 400)
}
Every leap year is every 4th year. To not overcomplicate things when using just the regular date and calendar, all you need to do is to check if the modulo 4 of year = 0, you can do this simply by checking:
C++ / Java: leapyear = year % 4; if (leapyear == 0) { // we got leapyear}
Visual Basic: leapyear = year mod 4: if (leapyear = 0) then ' we got leapyear
// isLeapYear will be TRUE if the value of "year" represents a leap year:
bool isLeapYear = (year % ((year % 100)>0 ? 4 : 400)) == 0;
// Perhaps, most succinct, but NOT most efficient because 100th year test is performed every time
bool isLeapYear = (year & (year % 25 != 0 ? 3 : 15)) == 0;
// Most efficient leap year test
// See: http://stackoverflow.com/questions/3220163/how-to-find-leap-year-programatically-in-c/11595914#11595914
bool isLeapYear = (year & 3) == 0 && (year % 25 != 0 || (year & 15) == 0);
— Preceding unsigned comment added by 37.196.158.254 ( talk) 01:14, 11 January 2016 (UTC)
This edit by [User:156.61.250.250]] asserts "Averaged over the long term, the vernal equinox year is equal to the mean tropical year, which is the same as the time between successive mean vernal equinoxes." But as our article Tropical year and the numerous sources cited in that article make clear, a mean tropical year is not the same as the time between successive mean vernal equinoxes (if indeed the term "mean vernal equinoxes" is even defined by the astronomical community. One highly authoritative source, the The Astronomical Almanac Online! (Glossary) does not define "mean tropical year" but defines "year, tropical" as
the period of time for the ecliptic longitude of the Sun to increase 360 degrees. Since the Sun's ecliptic longitude is measure with respect to the equinox, the tropical year comprises a complete cycle of seasons, and its length is approximated in the long term by the civil (Gregorian) calendar. The mean tropical year is approximately 365 days, 5 hours, 48 minutes, 45 seconds.
This is clearly different from "time between successive mean vernal equinoxes."
Even if some plausible explanation could be contrived to show the statement is true for some interpretation of "mean" and some interpretation of "averaged over the long term" it is not helpful to include a claim that is not supported by a reliable source and uses language differently from how it is used by the astronomical community. Jc3s5h ( talk) 14:47, 2 March 2015 (UTC)
mean equinox and equator: the celestial reference system determined by ignoring small variations of short period in the motions of the celestial equator and ecliptic. Thus the mean equinox and equator are affected only by precession. Positions in star catalogs are normally referred to the mean catalog equinox and equator of the beginning of a Besselian year.
The problem with terms like "vernal equinox year" and "(mean) time interval between two successive spring equinoxes" is that these terms are not defined. This is an encyclopaedia, and our mission is to define terms for the benefit of our readers. 156.61.250.250 ( talk) 11:44, 7 March 2015 (UTC)
P.S. See
File:CompareTropicalYears.png for a visual graph...
AnonMoos (
talk) 16:11, 19 July 2015 (UTC)
For a more thorough discussion of tropical, equinoctial and solstitial years see The Lengths of the Seasons (on Earth) by Dr. Irv Bromberg of the University of Toronto. He gives their lengths in terms of the number of mean solar days increasing in length at an average rate of 1.75 ms/century as well as atomic days of 86,400 SI seconds per day. He presents their sinusoids using many multicolored graphs up to ±100,000 years, some with the mean lengths of various calendars. He used numerical integration via SOLEX designed by Professor Aldo Vitagliano of the University of Naples, in contrast to the polynomials used by Jean Meeus valid for only a limited period of time. Although Meeus discusses the lengthening mean solar day, his tabulations and graph of the lengths of the various years use ephemeris days, identical to atomic days. — Joe Kress ( talk) 21:48, 2 January 2019 (UTC)
The following discussion is closed. Please do not modify it. Subsequent comments should be made on the appropriate discussion page. No further edits should be made to this discussion.
Should the phrase "peer-reviewed" be used in connection with stackoverflow in a way that suggests stackoverflow.com contributions are peer reviewed? In particular see this recent edit. Jc3s5h ( talk) 22:44, 9 December 2018 (UTC)
(Comment by author of edit in question: Not every contribution to Stack Overflow is purported to be "peer-reviewed". At issue, is Verifiability and Reliability: "Base articles on reliable, third-party, published sources with a reputation for fact-checking and accuracy." Stack Overflow CAN BE such a source. Over many years, heavily up-voted and moderator-scrunitized contributions to Stack Overflow certainly do gain legitimate peer-review. From Peer review: "Peer review requires a community of experts in a given (and often narrowly defined) field, who are qualified and able to perform reasonably impartial review." Stack Overflow is such a community of experts and its voting and moderation scheme ensures the highest-quality contributions are vetted. Rigorous Scholarly peer review should not be confused with or cited as a tool to detract from legitimate, "Verifiable" and "Reliable" peer-reviewed sources.) — Kriceslo ( talk) 10:04, 10 December 2018 (UTC)
There is no consensus to remove the pseudocode in the "Algorithm" section or replace it with code from a programming language. The consensus is that English is more broadly understood by readers than code and that code would require an explanation in English which would add unnecessary duplication to the article. Some editors recommended adding external links that contain code for the leap year algorithm.
Should Leap Year page include a computer programming example on how to calculate leap years? The Leap Year page is cited by numerous computer programmers [6] [7] and is used as a reference by programmers for information on how to calculate whether a given year is a Leap Year. Editors of the Leap Year page argue WP:NOTHOWTO (but nevertheless provide a textual algorithm). However, WP:BB argues that providing a real programming example in the very place that is turned to by many programmers makes the encyclopedia better ( WP:FATRAT). A single one-line programming example (in the vastly common C programming language) is proposed. — Kriceslo ( talk) 09:38, 10 December 2018 (UTC)
I have deleted the Hindu calendar section, mostly because it was unreferenced. Nachum Dershowitz and Edward Reingold in their book Calendrical Calculations 3rd ed. (Cambridge University Press, 2008) include two relevant chapters: chapter 9, "Old Hindu Calendars", and chapter 18, "Modern Hindu Calendars". The later chapter on p. 275 indicates there are over 30 variations of the Hindu calendar in active use.
This section should not be restored until a knowledgeable person with access to appropriate reliable sources to cite can create a version that accounts for all the different versions, discuss their relative popularity, and describe the leap month for one or more of the popular versions. -- 13:56, 9 May 2019 Jc3s5h
Wouldn't it be a good idea to somewhere in this article to give a list of the historical leap years in Julian Calendar?
As far as I know, the list goes something like this: 45 BC, 42 BC (*), 39 BC, 36 BC, 33 BC, 30 BC, 27 BC, 24 BC, 21 BC, 18 BC, 15 BC, 12 BC, 9 BC, AD 8 (**), AD 12, ...
(*) Julius Caesar decreed a leap year every 4 years but he was assassinated and the people who took over administration of the calendar screwed up and made a leap year every 3 years instead. When Augustus took over he declared no leap years between year 8 BC and 8 AD.
(**) I am unsure if year AD 8 was a leap year or not, but it is certain that year 12 and every 4 year after 12 was a leap year until Gregorian calendar took over. I am also certain that year 5 BC, 1 BC and AD 4 was all common years and not leap years. — Preceding unsigned comment added by AlfSalte ( talk • contribs) 07:25, 4 July 2020 (UTC)
In the conversation at the beginning talking about the reason for the leap day and the calculation for them, should there be a mention of why all of this is needed? There is a mention in the first section, Gregorian Calendar, showing the calculation of leap years resulting in 365.2425 days. I've read in several places (although do not have a definitive source) that the actual astronomical year is approximately 365.23 days. If someone can find a reference to this, should it be added to the header discussion to reinforce the reason for leap years? 19:27, 12 December 2019 (UTC) -- Preceding unsigned comment added by 198.70.201.220 ( talk)
User:John_Maynard_Friedman -- It's obvious from the structure of Kalends, Nones, and Ides etc, that a remote ancestor of the Roman Calendar as we know it must have been originally lunar. However, the immediately previous Roman calendar, which Julius Caesar changed in 45 B.C. was neither "Lunar" nor "Lunisolar". It was a rather odd entity where months no longer kept in phase with the moon, but the basic year length wasn't close to 365 days either. Every few years, a 13th month (sometimes called "Mercedonius") was inserted after February 23rd or 24th to keep the calendar in sync with the sun -- but the priests who were in charge of the intercalation were often incompetent and/or more concerned with shortening the terms in office of their enemies, or lengthening the terms in office of their friends, than in astronomy, so it had a tendency to drift out of sync with the tropical year. In 190 B.C. there was a solar eclipse which took place on July 11th of the Roman calendar as it then existed, but the date is March 14th according to modern calculations, so that the calendar was already pretty messed up (and probably no longer lunar) even back then... For more than you could possibly want to know about the pre-45 B.C. Roman calendar, see the book The Calendar of the Roman Republic by Agnes Kirsopp Michels... AnonMoos ( talk) 16:21, 8 December 2020 (UTC)
AnonMoos, when you wrote "(rather than one which was either strictly lunar or strictly solar)", did you intend to write "(rather than one which was neither strictly lunar or strictly solar)" ? -- John Maynard Friedman ( talk) 19:49, 8 December 2020 (UTC)
The intro section in #Julian calendar has been changed so often that it no longer reads sensibly. I don't have access to Cheney's A Handbook of Dates for students of British History but I suspect it is clearer than our current "The Romans treated leap day as a second sixth day before the Kalends (first day) of March, in Latin ante diem bis sextum Kalendas Martias." Should this read "The Romans treated leap day as a second sixth day in the week before the Kalends (first day) of March"? Even if it did, I can't see how that would have the effect of doubling 24 February. Would someone clarify, please? --
John Maynard Friedman (
talk) 07:49, 20 April 2021 (UTC)
Because the Romans used ' inclusive counting', "the sixth day before the Kalends of March" is reckoned by counting backwards from – and including – the first of March. February had an invariable 28 days (the leap day not being counted), so 28 February was the second day 'before' the Kalends and thus 24 February was the sixth day.
I find that the leap year algorithm can be clearer if rephrased as
if (year is
divisible by 400) then (it is a leap year)
else if (year is divisible by 100) then (it is a common year)
else if (year is divisible by 4) then (it is a leap year)
else (it is a common year)
instead of
if (year is not
divisible by 4) then (it is a common year)
else if (year is not divisible by 100) then (it is a leap year)
else if (year is not divisible by 400) then (it is a common year)
else (it is a leap year)
-- 201.229.5.234 ( talk) 12:35, 4 June 2021 (UTC)
An editor has identified a potential problem with the redirect List of leap years and has thus listed it for discussion. This discussion will occur at Wikipedia:Redirects for discussion/Log/2022 March 10#List of leap years until a consensus is reached, and readers of this page are welcome to contribute to the discussion. GeoffreyT2000 ( talk) 18:19, 10 March 2022 (UTC)
I am not particularly a fan of this graph:
I'm sure it's accurate enough, but it seems to have some presentation issues. Setting aside that it renders too wide and blows out the page width of the article, the (IMHO far greater) sin it commits is displaying a Y axis populated with dates like "June 20.5", "June 21.5", and "June 22.5". That's not a real thing.
The file is SVG, so in theory those issues could be corrected by hand-editing the graph. It isn't immediately obvious how one would go about actually regenerating the graph, though, since I've downloaded the software that purportedly supplied the data and I can't find any options for getting such a graph out of it. Unless perhaps the original uploader pulled the data points out of the source code, and graphed them some other way. FeRDNYC ( talk) 00:57, 18 October 2022 (UTC)
It is interesting that until the start of the year was moved from March 25 to January 1, no leap year actually contained a leap day. For example, the leap day for 1604 was Feb 29 1603. 2600:4040:5D30:4800:6416:83BB:F540:FFC9 ( talk) 14:53, 16 December 2022 (UTC)
References
The current text describes the 24 February bissextile day, then jumps to only the churches continuing to use it. We have nothing on when and where the practice changed? Anyone? 𝕁𝕄𝔽 ( talk) 16:42, 19 December 2022 (UTC)
Found it! (well, -ish).
Etymologically it is the double sixth day before the Calends of March, i.e. 24-25 February. But in spite of Edward I's ordinance and Seymour's meticulous observance thereof as late as 1552, it is clear that the bi-sextile day had in common use lost its etymological meaning. It might even seem that in fourteenth and fifteenth centuries, having cast loose from etymological moorings, it drifted up and down through February and even occasionally into January. As early as 1352 we find a chancery clerk dating an item on the close roll '29 February' yet exactly two centuries later Seymour adorns his Commons journal with precise repetition of the Roman style. In interval we find on the patent, close, or 'fine' rolls 29 February 1376, 1380, 1401, 1404, 1406, 1408, 1472 (thrice), 1481, a 1484 (twice); and it looks as though the bi-sextile day was settling down on its unetymological date of pridie Kal. Marti. But the fact that we find it in 1401 and 1406 as well as in 1404 and in 1481 as well as in 1484, not to mention Seymour's classical reaction, indicates a good deal of chronological hesitation. This is confirmed by still stranger aberrations: in 1393 we had '30 February', and again three times in 1484 (in addition to 29 February), and once in 1508 without a 29 February. Even more extraordinary are the '33 February' in 1493, the '32 January' in 1388, and the '33 January' in 1473." In 1512 we have a '29 February for leap year, but later in Henry VIII reign there is a distinct but natural tendency to take refuge in the ambiguous ultimo. How far Seymour's reaction was representative I do not know; but in the whole of the patent rolls, from Edward VI's accession down to the end (1560) of the latest published volume of the calendar, I have not found single 29 February. Many of the patents are undated and some omit either the day of the month or the month itself; but the only positive anomalies I have noted are the '31' November 1547 and a patent dated 25 December.
— A F Pollard "New Year's Day and Leap Year in English History" (p. 187) The English Historical Review Vol. 55, No. 218 (Apr., 1940), pp. 177-193 (17 pages) https://www.jstor.org/stable/553864
So, like a number of writers I found, I think we have to hide behind the vague "middle ages"? Although "about the fifteenth century" doesn't seem unreasonable if we cite Pollard? Comments? -- 𝕁𝕄𝔽 ( talk) 21:20, 20 December 2022 (UTC)
[I also recommend Google Lens I don't fancy my chances of transcribing those extracts correctly.] -- 𝕁𝕄𝔽 ( talk) 01:07, 22 December 2022 (UTC)However that may have been, the bi-sextile day was the sixth day, counted backwards according to the Roman system, from 1 March; it fell on 24 February, which was counted twice. But there were obvious disadvantages in having two days of the week on one day of the month, though no doubt it produced the well-known surname of Doubleday; and the Romans adopted the practice of differentiating the two by calling 24 February the 'posterior' bi-sextile day, and the 25th the 'prior' bi-sextile day, the 24th being behind, in their backward reckoning, the 25th day. This Roman practice was meticulously followed by John Seymour, the clerk of the commons in February 1552 when, after the heading Mercurii, 24° Februarii' in his journal, he has 'Jovis, quoque 24° pr' dies bisext."
POSTSCRIPT: Cheney (2000) [1945] (p. 8) is more explicit:
Christian festivals in a leap year
An anomaly arising from the Church’s adoption of the Roman calendar requires brief consideration. Using the Roman calendar, The Intercalary Day (bis VI Kal. Mart.) preceded the common VI Kal. Mart. When the simple numbering of days was adopted, the intercalary day appeared to be 29 February, but canonically it was 24 February, the exact equivalent of bis VI Kal. Mart. In leap years, therefore, St Mathias was commemorated on 25 February rather than 24 February, which was counted as Vigilia S. Matthei apostoli. This came to be regarded as a popish custom in England, and in the 1680s St Mathias came to be kept on 24 February, and the saints of the remaining days of February were not postponed; 29 February became de facto the intercalary day.
I will see how best to integrate that, since it is quite emphatic and Cheney is the RS (though I prefer Pollard's cockup theory and he cites his sources). -- 𝕁𝕄𝔽 ( talk) 16:58, 27 December 2022 (UTC)
The series of edits made by John Maynard Friedman on December 21, 2022, seems to conflate two potentially distinct changes. The first change was going from the idea of a double-day with a single date to two days with distinct dates. Before the change, in a leap year, February 24 lasted 48 hours and February contained 28 days. The second change, which might have occurred at the same time as the first change, or later, is to consider the intercalary day to be February 29 rather than February 24.
The mere fact that a calendar shows 29 days for February does not necessarily mean that February 29 was the intercalary day. As the movement of the [f]east of Saint Matthias shows, February 24 could still be considered the intercalary day even with a calendar that shows a February 29. If the drinking law recognized the first change but not the second, I suppose a US person born February 27, 2003 would have to wait until February 28, 2024 to buy a drink in a bar. Jc3s5h ( talk) 21:47, 21 December 2022 (UTC) Fixed typos pointed out by JMF at 01:23 December 22, 2021 UTC.
———
But in spite of Edward I's ordinance and Seymour's meticulous observance thereof as late as 1552, it is clear that the bi-sextile day had in common usage lost its etymological meaning. It might even seem that in the fourteenth and fifteenth centuries, having cast loose from its etymological moorings, it drifted up and down through February, and even occasionally into January.
In 1551/2 the new clerk of the lords also ignores the etymological bi-sextile day and has Tuesday 23, Wednesday 24, Thursday 25, Friday 26, and Saturday 27 February. He has then an adjournment to Thursday, 3 March. So, unlike his colleague in the Commons, he abstains from a bi-sextile 24 February, while an adjournment makes it doubtful whether he visualized a 29 February or a 'bi-sextile' 1 March like his predecessor in 1543/4.
The O.E.D. describes the word 'bis-sextile' as 'obsolete', and we may conclude that it became so during the latter half of the sixteenth century, the process having taken at least two hundred years since a chancery clerk dated a document '29 February' in 1351/2.
I have begun to rework the section to take into account this discussion. It will take a few days as I don't have a lot of free time just now. -- 𝕁𝕄𝔽 ( talk) 08:28, 27 December 2022 (UTC)