Talk:Leap year

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[edit] Discussion

What does this mean? It requires more explanation I think.

"By occasionally adding an additional day (in the Gregorian Calendar this is February 24) to the year, making it 366 days long instead of the usual 365, this can be corrected. (It is commonly believed that Feb. 29 is the added day, but that is technically incorrect.)"

I just added a detailed explanation while you were writing... -- Tompeters

The term 'going forward' is an abomination which is unfortunately common in present day parlance. Could that be changed to 'in the future.'

—Preceding unsigned comment added by 150.135.161.161 (talk) 23:09, 24 February 2008 (UTC)

Which day is added doesn't matter for most purposes except for Saints days. Suppose we have some Saints St. A, St. B, St. C, etc. In a non-leap year their feast days are celebrated on: Feb 23, St. A; Feb 24, St. B; Feb 25, St. C; Feb 26, St. D; Feb 27, St. E; Feb 28, St. F. On a leap year, their feast days are celebrated on: Feb 23, St. A; Feb 24, nothing; Feb 25, St. B; Feb 26, St. C; Feb 27, St. D; Feb 28, St. E; Feb 29, St. F. If the leap year was insertered on Feb. 29, it would be instead: Feb 23, St. A; Feb 24, St. B; Feb 25, St. C; Feb 26, St. D; Feb 27, St. E; Feb 28, St. F; Feb 29, nothing.

Or at least thats how things where celebrated for centuries... maybe in more recent years they've modernised the system a bit. But traditionally at least, Feb. 24 was the extra day, not Feb. 29. -- SJK

How do we find out if this is still the practice? Anyone?

"This one day behind" is only the average over all the seasons. The Southern solstice is moving later in the tropical year, so fast that the Gregorian calendar is running ahead it by almost one day per 4000 years."

How is the solstice moving? As far as I can tell this would require days to be different length than described in the text of the article. So which is correct?

The solstice is moving, with the equinox, due to precession. My text on the tropical year explains why and how this effects the duration of the year, as measured from any of these points. Of course you have to use a stable clock, i.e. ephemeris time, not universal time which we use in civil life but is linked to the erratic rotation of the Earth. -- Tompeters.
The movement of the solstice is big enough to show up in Universal Time, but would change from 1 day per 4000 years more rapidly and less predictably than for ephemeris time. For calendrical considerations, Universal time or some other measure of the real day must be used. -- Karl Palmen

So you are saying that a new day is inserted after February 23rd, and all the days after the 24th are renumbered, so that the days go up to 29 instead of 28. However, I would recommend rewriting it a bit to make that a little more clear. That being said, I don't celebrate Saints days myself, and intuitively and logically I would say that February 29 is the leap day. I am curious if the idea that it is the 24th is simply a religious rather than a calendar definition, a way of dealing with leap years that religious people came up with to deal with it. Is there an "official", secular definition of the leap day that states that it is February 24?

Ah, I see that a more detailed explanation has been written as I was commenting on it. Never mind.
I don't celebrate Saints Days myself either. You have to remember that centuries ago, when the Feb 24th rule was adopted, the secular/religious distinction didn't really exist like it does today. It might be a Christian development, it might be of Roman origin (related to the Ides and Nones and Kalends and so forth), I don't really know. I don't think there is any "official secular definition" today of which day gets added, in the sense that traditionally the day was Feb 24th. -- SJK

The odd bit about February 24th is mainly seen in the pre-Vatican II Catholic calendar now, where saints from the 24th to the 28th get bumped one day later, but it makes perfect sense if you use the Roman calendar. March 1, to a Roman, was the Kalends of March, and the 24th would be "sexto Kalendas Martii", "the sixth day before the Kalends of March", and the 23rd was "septimo Kalendas". In leap year, the 23rd stays as "septimo", the leap day is the 24th ("bis sexto", "again the sixth", hence the word "bissextile"), and the 25th is "sexto Kalendas". Now that we number the days from 1-31, the 29th is the additional number, but to a Roman, that extra sexto Kalendas was the leap day, and that's the one that stuck with us. PaulGS 01:43, 22 June 2006 (UTC)

Could someone elaborate on the comment that the 4000-year rule doesn't gain any accuracy? EB claims that it is part of the calendar rules. --AxelBoldt

Not the standard Gregorian calendar rules. I think though when some Orthodox churches adopted the Gregorian calendar, they adopted something like the 4000-year rule as well; but it will be centuries yet before there is any difference between the standard Gregorian and the Orthodox Gregorian calendars. -- SJK
This is the first time I hear of the "4000 year rule". I do know that the Orthodox churches adopted a rule of dropping the leap day in century years divisible by (some list of numbers here), but I do not have the details. IIRC the first difference with the Gregorian scheme would be in the year 2800 or thereabouts. Also, as the text on the page implies, it is pointless to try to refine the approximation by dropping another day after thousands of years, because the length of the year itself will have changed considerably by then. -- Tompeters

Shouldn't this page be called "leap day", because we talk about adding a whole day, not a whole year? cf. "intercalary month" or "leap month", for adding a month to a year in a luni-solar calendar to keep it roughly in sync with the tropical year. Anybody? -- Tompeters

To a trained scientist, saying "is 365.2422 days" might be understood to mean "365.2422 days, accurate to four decimals". But to ordinary English speakers such as the intended audience here, it means "exactly 365.2422 days", and since that's not true, I've restored the "about". If you can think of a better way to reword it so that it does not imply that the figure is exact, that would be fine too. --LDC

Someone has changed the article from speaking of the mean tropical year to the vernal equinox year. What is the difference? And while certaintly the vernal equinox year was what concerned Pope Gregory -- keeping Easter in the right season -- does the same hold true for modern use of the calendar? Modern astronomers appear to prefer to use the mean tropical year to the vernal equinox year. -- SJK

If you read tropical year you should see that the exact length of the tropical year depends on the start of the tropical year. The mean tropical is the average for all start points. The difference is presently almost 0.0002 days (1 day per 5000 years) and is increasing.
It is a common error to define the tropical year length as the vernal equinox year length and then use the value of the mean tropical year. -- Karl Palmen
The cause of the differences in the length of the various tropical years is due to the eccentricity of the Earth's orbit. The equinoxes and solstices drift by a certain angle in relation to the background stars, and the length of time it takes the Earth to pass through this angle differs due to the eccentricity of the orbit, as described by Kepler's second law of planetary motion. --B.d.mills 02:44, 8 Mar 2005 (UTC)
I have recently researched the March equinox tropical year versus mean tropical year debate online, and the conclusion I drew from this is that astronomers are uncertain as to whether the year is supposed to track the March equinox tropical year or the mean tropical year. I would guess that the year was supposed to follow the March equinox because in 1582 when the Papal Bull was decreed, Kepler's laws of planetary motion had not yet been discovered, and the Pope was concerned over the timing of Easter which occurs near the March equinox. However, it would not be reasonable to expect the March equinox to remain the sole determinant of the length of the year, because over tens of thousands of years its length will vary considerably more than the length of the mean tropical year, and the March equinox is no more special than any other equinox or solstice, astronomically speaking. --B.d.mills 02:44, 8 Mar 2005 (UTC)

Hi, I've heard it's already decided that year 4840 will NOT be a leap year. Anyone knows details please? See this czech article (sorry folks, I know there's just few of us who understand the funny language). Cheers, --MarSes 12:36, 11 Mar 2005 (UTC)

It's not true. In case the gregorian calendar will still be used in that year it will be leap year, in case any other calendar is adopted - who will know what calendar will be adopted with what leap year rule. What is true - at around that time the calendar has about one day difference with the astronomical spring, so a fix of the calendar may take place then. andy 12:57, 11 Mar 2005 (UTC)

The article states that the next leap year is 2010 (apparently the page was edited while I typed this; it no longer contains this). The next leap year is 2008, not 2010.

In any case, stating when the next leap year is seems pointless. If it is going to be in the article, at least make it accurate. MWBL 20:40, 6 January 2007 (UTC)

It was pure vandalism, which I nuked as soon as I was aware of it... AnonMoos 19:12, 7 January 2007 (UTC)
Ah, that makes sense. I just don't see how someone enjoys putting a false leap year in... MWBL 12:04, 16 March 2007 (UTC)

[edit] Reason for "leap"

I removed this entry added by Jadedaemon:

Why is it called a `Leap Year'?
The Leap Year Day once had no recognition in English Law. The day was `leapt over' and ignored.

This may just be poorly worded. Consider the Statute of Henry III "de Anno et die Bissextili" (On the year and the bissextile day, 1236 or 1256) which specified that the "bissextile day" and "the day next going before" are to be counted as one day. This shows that the day was recognized in law and that it was not called a leap day at that time. But if both days were counted as one day, then any period which included it would have the same number of days in both common years and in leap years, so the leap day would seem to be ignored. Nevertheless this appears to be speculation. The first usage of "leap year" cited by the OED may be instructive. I have also thought that "leap" was derived from the dominical letters used to determine which days were Sundays in any year. When a leap year occurs, all dates after the first two months jump over a weekday compared to the previous year, so a dominical letter from a common year to a leap year appears to be missing (it actually exists during the first two months only). — Joe Kress 07:26, 27 September 2005 (UTC)

Actually a leap year has two dominical letters. The first is for the first two months and the second for the remaining ten months. — Karl Palmen 12:45, 27 September 2005 (UTC)

[edit] Patrick and Bridget anecdote

The St. Patrick and St. Bridget thing as quoted here is an obvious jocularity... AnonMoos 17:47, 24 September 2006 (UTC)

It not a jocularity—it is a tradition as stated. Whether it is true would require substantial research. I don't doubt it because at the time women were regarded as property with virtually no rights. The citations required by Wikipedia are provided for these quotes. — Joe Kress 19:58, 25 September 2006 (UTC)
No, it's not a "tradition" -- it's an intentionally facetious contrived anecdote. AnonMoos 03:14, 26 September 2006 (UTC)
P.S. I can guarantee you with 100% certainty that it's not true based on common sense and very basic chronological considerations.AnonMoos 03:16, 26 September 2006 (UTC)
Duh, and I am 100% sure that St.Patrick did not expell any snakes from Ireland. But it is a traditional story with a moral, just like the one with St.Bridget: they are still worth to be told, despite being fabulations dating from whenever: if only because they tell us something about mentality of that time and give a rationale for certain customs. Tom Peters 10:44, 26 September 2006 (UTC)
What time? The mid-nineteenth century? AnonMoos 15:26, 27 September 2006 (UTC)
Maybe. That is history too. At least it invents a justification for the custom both of proposing by a woman in a leap year, and buying it off by a gown and a kiss. If it bothers you that it is not genuine historical fact, then removing it is not the way to go because then you'll have to delete 99% of saint lives'. Rather, specify that the story dates from the 19th century, but do provide a reliable reference to prove that assertion. "common sense and chronology" are not sufficient. Tom Peters 08:22, 28 September 2006 (UTC)
Whatever -- however apocryphal and miracle-mongering the traditional Saints' lives may have been, they were generally written 500 or more years ago (while I rather strongly doubt that this Patrick-Bridget anecdote was written before the late 18th century, and the second half of the nineteenth century seems rather more probable). Traditional lives of saints rarely included deliberate contrived jocularities, either. And I wonder whether it was even written by an Irish person at all -- it seems to display signs of straining overhard to include stereotypical "local colour" (see Irish bull etc.). I only wonder that the author of the piece managed to refrain from including "colleen" and "blarney" in the anecdote! (With much effort, no doubt...)
The upshot is that the presentation of this anecdote in the article is very misleading by implication, and it is given much more prominence in the article than its real importance would seem to demand. If someone doesn't fix these problems fairly soon, then I'll be doing it myself. AnonMoos 23:13, 28 September 2006 (UTC)

[edit] Oppose

I don't think this article should be merged into Leap Year because its good to have different articles. If the articles are merged then the info will be harder to find.

[edit] further explaination needed

The explaination of a leap year in the gregorian calendar does not make sense. It does not mention that a leap year occurs in years divisable by 4 with the exception to the rule of years divisable by 100 but not by 400. I hope what I wrote makes sense. the every 4 years part should be added Phooph 15:45, 30 January 2007 (UTC)

[edit] Source needed for "so that the date of Easter remains correct"

I believe a source is needed for the claim that the reason it was introduced was "so that the date of Easter remains correct." The sources in the article give only the Vernal equinox as the reason (the first part of the sentence in question). I see some talkers a few years ago said their research found this to be true, but the current references do not contain this information. - Davandron | Talk 20:45, 12 February 2007 (UTC)

That's pretty much what it says in Chapter 19 of Mapping Time: The Calendar and its History by E.G. Richards (ISBN 0-19-282065-7). The astronomically sophisticated were bothered by both types of discrepancies, but most Christians who were not astronomers were probably much more worried by the possibility of celebrating Easter on the "wrong" day than they were by a discrepancy in the calendar date of the equinoxes, so that Richards considers it unlikely that a reform would have occurred if the equinox calendar date had been the only problem:
  • Much more serious for the medieval Church was the observation that the dates of Easter were starting to fall on inappropriate days. It was this that was the spur to the whole reform movement. The drift of the vernal equinox was, in itself, of relatively minor importance. -- p. 240.
AnonMoos 23:19, 12 February 2007 (UTC)

[edit] Bisextile day

Bisextile day redirects here, but is not explained. Christoph Päper 12:44, 18 February 2007 (UTC)

In the old Roman calendar, the leap day was inserted as a second Feb 23rd (rather than a new Feb. 29th at the end of the month), and Feb 23rd. (like all the days of every month after the "ides" of the month) was numbered by counting backwards from the 1st. day of the next month -- it was the sixth day (using Roman "inclusive counting") before March 1st. Bissextilis meant "For the second time, Six" (i.e. the second day considered sixth back from March 1st.). AnonMoos 16:16, 18 February 2007 (UTC)
It's explained under the heading Leap day. I've changed the redirect to that heading. — Joe Kress 20:54, 18 February 2007 (UTC).

[edit] List of leap years

Somebody should put a list of past and future leap years (http://kalender-365.de/leap-years.php), I would've myself but I wasn't sure where...--Sunny910910 23:00, 23 May 2007 (UTC)

That's almost as pointless as a list of numbers that end with 4. You too can calculate leap years given the info in this article. +mt 01:35, 4 July 2007 (UTC)

I agree with the first guy. Most people will just want a list of the next few leap years, and maybe the last few. At least put the algorithm into plain English. The current computer program-style explanation is ridiculously obscure. —The preceding unsigned comment was added by 90.200.14.205 (talk) 17:21, August 21, 2007 (UTC)

Between 1901 and 2099, if the number of the year is evenly divisible by 4 (without remainder), then it's a leap year (and otherwise not). Since I doubt that you were born before 1901 or will live past 2099, that rule of thumb would seem to be adequate for all immediate proactical use. AnonMoos 08:41, 22 August 2007 (UTC)

It would just be easier to look at a list that have to get the calculator out. —Preceding unsigned comment added by 70.248.232.32 (talk) 02:31, 16 October 2007 (UTC)

[edit] So....when was the last leap year?!?! ( before 2007 )

WHEN was the last leap year?!?!

Between 1904 and 2096 inclusive, every fourth year is a leap year in the Gregorian calendar, including 1996, 2000, 2004, 2008, 2012, etc. So the last leap year was 2004. In the United States, leap years coincide with Presidential election years between 1904 and 2096. — Joe Kress 06:46, 29 June 2007 (UTC)

[edit] A compliment on your graphic

The graphic [1] is one of the most clear consice examples of communicating the error between the Tropical year and Calendar year I have ever seen. Artoftransformation 23:28, 24 July 2007 (UTC)

Great diagram. Sagittarian Milky Way (talk) 02:39, 3 February 2008 (UTC)

[edit] Birthdates

Do any countries legally use the "bissextile" system (i.e. 24 and 25 february in a leap year = 24 february in a non-leap year, 26-feb for leap year = 25-feb for non-leap year, etc?) for these purposes? —Random832 17:56, 21 September 2007 (UTC)

Don't know, but traditionally Catholic saint's days were observed in this manner. AnonMoos 10:49, 14 November 2007 (UTC)

[edit] February 30

Most of us believe that February never has 30 days. Well, that's not exactly true. In 1712 in Sweden and Finland they had a double leap year because a leap day around 1700 got dropped, and the Swedish calendar didn't get synchronized, so that second added day in 1712 put them back on the Julian calendar. 24.180.186.24 (talk) 03:33, 10 January 2008 (UTC)Unknown

[edit] 1.wow!

there is nothing on here about leap year who even likes it any ways?? it makes no sense and i dont think that it has anything to do with daily life!!! so who cares about it!! so what if it throws off a little!! it would make everything else so much easier!! —Preceding unsigned comment added by 164.58.165.165 (talk) 20:02, 27 February 2008 (UTC) happens every other year

[edit] Algorithm

Is this really necessary? i have seen no precedent for explanation via algorithm, and I feel like the prior explanations do a better job than the code.The freddinator (talk) 04:52, 29 February 2008 (UTC)

Yes, it is really necessary. I know of at least two people who went here looking for it and were happy to have found it. Ysth (talk) 10:06, 3 March 2008 (UTC)

[edit] Mathemtical pickiness

The opening paragraph reads...

In the Gregorian calendar, the current standard calendar in most of the world, most years whose division by 4 equals an integer are leap years.

It should be "equals a natural number" not an integer.

I don't have an account, but my name is Steven Oliver for further reference. --70.90.250.13 (talk) 13:13, 29 February 2008 (UTC)

Apparentley, wikipedia is not at all reliable because everyone can edit it.

So most people write absoloute rubbish. It is not reliable, as i have proved by deleting everything that previous people have writen. aren't i clever. so guess what? i'm clever. i repeat : wikipedia is nopt reliable. do not use it. especially for coursework. My A level History paper counted for nothing because one of my sources was wikipedia, and the examiner discualified me. I'm just trying to help is all.

):):):):):):):P —Preceding unsigned comment added by 80.177.228.194 (talk) 14:28, 29 February 2008 (UTC)
So if you are trying to help, why do so on an out of the way discussion page? With your paper, you must always use additional sources, and it is clearly stated in Wikipedia policies that Wikipedia is not accepted under most exam boards as a reliable source. Therefore, it is your own fault. microchip08 (talk) 21:02, 29 February 2008 (UTC)

[edit] 4000 AD

"4000 AD" should be "AD 4000" —Preceding unsigned comment added by 165.200.127.254 (talk) 15:29, 29 February 2008 (UTC)

[edit] Happy Leap Day

Zginder (talk) (Contrib) 15:47, 29 February 2008 (UTC)

[edit] Leaplings? Leapers? What are Leap Year Babies called? LEAPLE!!!

I have never heard of either term for Leap Year Babies until this week.

The term Leaplings appears to come from a mid-1990s children's book. http://www.wordspy.com/words/leapling.asp It's really cute until you are old enough to vote.

I read an article this week that said adult Leap Year babies were called Leapers. Oh Really?? Only since 1996...

I am VERY interested in the term for a Leap Year Baby because I am one. Leaplings is insulting if you are grown. Leapers is mediocre. I prefer Leaple.

Juniorgoddess (talk) 04:23, 1 March 2008 (UTC)

[edit] Removed NYT article link

Removed link to New York Times article [2] because it adds no real relevant facts beyond what was already contained in this Wikipedia article, but does contain some inaccuracies (such as implying that the Roman calendar was lunar before 45 B.C., and repeating some long-debunked historical nonsense about alleged "11 days" riots in England in 1752). AnonMoos (talk) 12:48, 1 March 2008 (UTC)

[edit] Easter

"The Gregorian calendar was designed to keep the vernal equinox on or close to March 21, so that the date of Easter (celebrated on the Sunday after the 14th day of the Moon that falls on or after 21 March) remains correct with respect to the vernal equinox.[3] The vernal equinox year is about 365.242374 days long (and increasing), whereas the average year length of the Gregorian calendar is 365.2425."

I think this is wrong. Easter date is based on the Ecclesiastical equinox which does not accurately track the astronomical equinox. This paragraph seems to imply that easter is chosen based on the true astronomical equinox. Gigs (talk) 17:21, 14 March 2008 (UTC)

Yes, but the Gregorian calendar was devised so that the ecclesiastical vernal equinox would track the astronomical vernal equinox as closely as is possible using very simple leap-year rules ("4 EXCEPT 100 EXCEPT 400"). The vernal equinox year was also more relevant for the devisers of the Gregorian calendar than the mean tropical year. A lot of articles on calendars complain about the discrepancy between the mean tropical year of 365.2422 days and the Gregorian year of 365.2425 days (the Revised Julian Calendar was even an attempt to "fix" this), even though the Gregorian calendar was actually more intended to approximate the vernal equinox yearof 365.2424 days... AnonMoos (talk) 18:42, 14 March 2008 (UTC)
The papal bull Inter gravissimas does state that its intent was to return the vernal equinox to March 21, and its rules were intended to prevent it from again receding from March 21, so its rules should have approximated the vernal equinox year. However, as of 1582 the vernal equinox year could not be measured with sufficient precision separately from other kinds of tropical years. Even though the Gregorian rules may seem to approximate the vernal equinox year, it just so happens that those rules result in a year (365.2425 days (decimally) or 365;14,33 days (sexagesimally)) which exactly equals the year given in astronomical tables available to the Gregorian reformers. Specifically, the years given in the Prutenic Tables and in its predecessor, the Alfonsine Tables, when rounded to two sexagesimal places are equal to the mean Gregorian year (see Gregorian reform of the calendar cited in Gregorian calendar#References). But the year of those tables was supposed to be the mean tropical year, not the vernal equinox year. So it is a fortunate accident that the Gregorian year is nearer the vernal equinox year than it is to the mean tropical year. — Joe Kress (talk) 10:15, 16 March 2008 (UTC)
Rounding to 365;14,33 is mentioned on page 99 of Gregorian reform of the calendar, where J.D. North refers to a note by Noel Swerdlow, The origin of the Gregorian civil calendar, Journal for the History of Astronomy 5 (1974) 48-49. Although North used rounded, a better term would be truncated since all three years listed were greater than 365;14,33. Specifically, these (tropical?) years were
365;14,33,9,57,... Alphonsine tables
365;14,33,11,12,... De revolutionibus (Copernicus)
365;14,33,9,24,... Prutenic tables
Their average value (disregarding the unstated terms beyond the fourth sexagesimal place) is
365;14,33,10,11 or 365.2425471 days
which differs considerably from the modern mean tropical year, 365.242190 days.
Gregorian reform of the calendar also mentions on page 103 that in 1583 John Dee explained how the vernal equinox year differed from the autumnal equinox year, using Copernicus's De revolutionibus and the Prutenic tables, although his values no doubt differed quite a bit from modern values. — Joe Kress (talk) 03:39, 24 March 2008 (UTC)

[edit] 128 Year rule.

Can anybody explain this nonsense?

A system of 128-year-based leap years has been proposed,[7] and it can be adopted directly without any modification to current leap year calculations until the year 2048 because no year between now and 2048 is divisable by 128. This rule gives a mean year of 365 + 1/4 − 1/128 = 365.2578125 days, which is 365 days, 6 hours, 11 minutes, and 15 seconds.

I don't think a missing leap year every 128 years means you subtract 1/128. Secondly, whoever did the calculation evidently missed the obvious, ie that the resulting year is far too long (over an hour a year), since the aimed-for result has to be closer to 365.2422, not larger than 365.25!!

Silas Maxfield (talk) 14:13, 1 April 2008 (UTC) I see where the error is now. I will make the calculations and modify it accordingly. Silas Maxfield (talk) 14:41, 1 April 2008 (UTC)