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This article is written in British English, which has its own spelling conventions (colour, travelled, centre, defence, artefact, analyse) and some terms that are used in it may be different or absent from other varieties of English. According to the relevant style guide, this should not be changed without broad consensus.

centuries have only one date for beginning and ending.

all centuries begin on January 1st on a year that ends with '01 and ends on December 31st with a year that ends with '00. Any other way is totally 100% wrong. Thus the 20th century began with January 1, 1901, and ended on December 31, 2000. That is why it was the 20th century. because it end with 20(00). This is the 21st century, because it started on January 1, 2001 and not on January 1, 2000, because that was the beginning of the last year of the last century. This is this century and it did start on January 1, 2001 and not before. And this century will end on December 31, 2100, because it ends the year with 21(00), not with December 31, 2099. This is the 21st century and that means it ends with the year 2100. It has nothing to do with leap years of anything else. The celebration that celebrated around the world at the beginning of this century was actually a whole year way to early. The majority of people and governments just plainly goofed up. Just like this decade starts on January 1, 2011 and it ends on December 31, 2020, not 2019 like too man people are already thinking about. I wish people would get this right.Bobbyr55 (talk) 01:46, 31 December 2014 (UTC)

An unnecessary split. Done without any discussion.

Why on earth did Dbachmann singlehandedly, without any discussion, split this article, remove nearly all info on the adoption of the G.C. and create this new article Adoption of the G. C. !? An uncalled for move AFAIC, done without any consultation.--Lubiesque (talk) 14:27, 24 January 2015 (UTC)

You should have weighed in at Misplaced Pages:Requests for arbitration/Dbachmann. — Preceding unsigned comment added by 156.61.250.250 (talk) 13:13, 25 January 2015 (UTC)

See also Talk:Old Style and New Style dates#Duplicate articles (March 2015) -- PBS (talk) 09:26, 9 March 2015 (UTC)

Last country to adopt the Gregorian calendar?

It says here that the last country to adopt the Gregorian calendar was the Soviet Union in 1929. I found articles (referred below) that mention that the Soviet Union changed to the Gregorian calendar on February 14, 1918. In fact, I found articles stating that the USSR actually abandoned the Gregorian calendar in 1929 in favour of the "Eternal Calendar" consisting of 12 months, each made up of 30 days split into six 5-day weeks. Later in 1932 they switched to 6-day weeks, only coming back to the Gregorian proper in 1940. Can someone please check these facts and edit the page? I've put some of the links below. The first one is pretty comprehensive, but the others will help you double check.

http://www.sras.org/russian_holidays

https://www.worldslastchance.com/ecourses/lessons/changing-weeks-hiding-sabbath-ecourse/18/20th-century-soviet-calendar-reform.html

http://history1900s.about.com/od/1920s/a/sovietcalendar.htm

So does that make it the last country to adopt the Gregorian calendar (i.e. in 1940) or does that title pass to someone else? — Preceding unsigned comment added by 14.97.86.240 (talk) 18:33, 13 February 2015 (UTC)

There is certainly some confusion that needs to be sorted out. Adoption of the Gregorian calendar#Adoption in East Asia says that Russia adopted it in February 1918.

The graphical Timeline says that Russia adopted it in 1918; it also says that the Soviet Union did so in 1922. That seems wrong for starters. Russia had already converted almost 5 years before the USSR ever came into formal existence in 1922, so it's not like the USSR started out under the Julian calendar and only later switched to Gregorian. No, the pre-existing Russian change-over simply extended to the new political entity that came into existence on 30 December 1922, and that cannot be characterised as an "adoption".

Then there was the Soviet calendar, which was in use between 1929 and 1940. That means that 1929 is the year that the Soviets abandoned the Gregorian, not adopted it. (The relevance of 1930 escapes me entirely.) Whether the re-adoption counts for the purposes of saying which was the last country to make the switch, I'm not sure, but if it does count, the relevant date would be 1940, not 1929. For comparison, when the French abandoned the French Republican Calendar in 1805 after 12 years of use, and re-adopted the Gregorian, we don't quote 1805 as the date of Gregorian adoption in France. We always refer to its original adoption there in 1582. So why make an exception for the Soviet Union? The fact that the country's name and organisation changed matters not.

I prefer to say that Russia adopted the Gregorian in 1918; the Soviet interruption 1929-40 deserves a mention later in the article and a link to Soviet calendar, but let us please get the dates right. -- Jack of Oz 21:43, 13 February 2015 (UTC)

I've been bold and made the above changes. But still feel free to discuss. -- Jack of Oz 23:10, 13 February 2015 (UTC)

The expert on this is Joe Kress. Feel free to ping him. See Soviet calendar where he makes it clear by references to the date on the pages of e.g. Izvestia that the U.S.S.R. never stopped using the Gregorian calendar.

The five and six - day weeks resulting in thirty - day months were grafted on to the Gregorian calendar - 360 days of work weeks and five or six public holidays outside making up the 365/366 day Gregorian year. Dates such as August 31 prove this. However, the White Russian armies in the 1920's (Orthodox) were not keen on the Bolshevik reform - and of course the Orthodox church still uses the Julian calendar. Authorities in far - flung provinces were slow to make the change, so it's perfectly true that the U.S.S.R. was not wholly Gregorian till 1929. 156.61.250.250 (talk) 16:41, 14 February 2015 (UTC)

You're noting the difference between formal promulgation and practical implementation. I am quite, quite, quite sure that many people and communities in Italy, Poland, Spain and Portugal did not immediately switch to the Gregorian calendar on 15 October 1582, either. There would have been resistance and delays in the British switchover in 1752, particularly in their overseas colonies. Of course there will always be problems in implementing a change like this. That would be true even today, let alone in the days before instant mass communication. However, the main thing we need to focus on here is that Russia formally switched to the Gregorian in February 1918. Details of the less-than-uniform implementation of that policy can appear if they're available, but in a lower profile location in the article. -- Jack of Oz 19:15, 14 February 2015 (UTC)

Considering that an encyclopedia article must be concise to be useful to the intended audience, I think it's OK to just mention the formal start of a change that was successful, and reduce emphasis (or even ignore) changes that were formally promulgated but weren't accepted by the populace and were later repealed.

An example of a somewhat recent change that has been slow to be accepted by the populace (and some governments) is the elimination of Greenwich Mean Time. If you ask the scientific community, they'll tell you it was renamed universal time in the 1930s. If you ask for an exact definition of GMT, they'll tell you there isn't one. Jc3s5h (talk) 13:45, 15 February 2015 (UTC)

I think it's useful to tell readers about the Eternal calendar and the French Revolutionary calendar. We mention the Decree of Canopus but that change never got off the ground at all. Regarding Jack of Oz's edits, he's done something with curly brackets but what's inside them doesn't seem to appear at all (at least not in my browser). Can you elucidate what's happening here?

Re Greenwich Mean Time, if you look inside the Astronomical Almanack (I haven't consulted it for some years mind) there's a note that astronomers do not use the term "Greenwich Mean Time" because it's ambiguous. But astronomers are not lawyers. Lawyers go back in time (the doctrine of legal precedent) and will happily tell you that Greenwich Mean Time is the same now as it was in 1971. 156.61.250.250 (talk) 14:33, 15 February 2015 (UTC)

Turkey and the Gregorian calendar

In 1917 the Gregorian calendar was adopted by Turkey (Ottoman Empire) but not the Christian era. The calendar agreed with the Gregorian calendar except on the number of the year. On Dec. 6, 1925 a decision was made by the Republic of Turkey to adopt the Christian era as well. — Preceding unsigned comment added by Ybgursey (talk • contribs) 17:31, 23 February 2015 (UTC)

See Adoption of the Gregorian calendar#Timeline. 156.61.250.250 (talk) 09:55, 24 February 2015 (UTC)

Which day is the leap day?

Is the leap day February 29 or February 25. In Roman terminology, February 24 was (and is) the sixth day before the kalends (beginning) of March. After the Julian reform, leap years were created by having two sixth day before the kalends of March, what we would call February 24 and 25. According to this article some Catholic feasts are observed according to their Roman nomanclature, as so-many days before the beginning of March, and seem to shift a day later when the modern method of counting from the beginning of the month is done.

On the other hand, secular dates that are set for the same date every year would occur on the date with the specified name, such as February 27, whether it was a leap year or not. But in the USA, I am not aware of any holidays or important national deadlines that are set for February 24 through February 28.

Another question is who is in charge? If the Catholic Church, Protestant churches, and the government all make their own choices, should we describe any one of the choices as the correct interpretation of the Gregorian calendar? Jc3s5h (talk) 14:47, 24 February 2015 (UTC)

I have found a source, Richards' 1998 book, which I have added to the list of references. Richards not only had his book published by Oxford university press, but also went on to write the "Calendars" chapter in the 3rd edition of the Explanatory Supplement to the Astronomical Almanac.

Richards (1998, pp. 100–101) indicates the leap day was inserted between 23 and 24 February, and named bis Kal. Mart while the Julian calendar was in effect and the practice was continued when the Gregorian calendar was adopted; the Roman Catholic Church was still using the practice when Richards wrote in 1998. The Anglican Church changed to regarding February 29 as the leap day in 1662, long before adopting the Gregorian calendar.

I would like to see a definitive source as to when the Roman Catholic Church changed to regarding 29 February as the added day, but have not been able to find one.

I believe the information should be in the article since the article covers both present and past usage of the calendar. Jc3s5h (talk) 14:54, 19 March 2015 (UTC)

Leap day is the bissextile day

The evidence presented for the leap day being the 29th of February is invalid. To see why, let's start with the Catholic evidence.

It is untrue that February dates after the 23rd have been cleared of commemorations as a cursory examination of the current Martyrologium Romanum will make clear. Look under 24 February, and you will see the rules for the bissextile day stated clearly, namely, that the day is inserted then. Furthermore, an examination of the Liturgia Horarum (on page 16 of, e.g., volume 2) shows that it clearly states that one dominical letter is used up to 24 February, and another after. While most of the saints in the Martyrology have days attached to the ordinal day of the month, not all do; four saints are assigned to pridie calendas martias, which is 29 Feb in bissextile years, and 28 Feb in other years.

It is untrue that counting days as ordinals of the month implies that the leap day is added to the end rather than inserted on sexto calendas martias. To illustrate this point, consider the 366th day of the year. It occurs only in leap years, and not in other years. So do we consider it the leap day? Ridiculous! In the same way, numbering the days in order does not mean that a day is inserted between pridie calendas martias and calendis martiis. Keying celebrations of saints days to the ordinal count, or not, tells us nothing about which day is inserted; that is simply the nature of ordinals.

I would like to see a definitive source as to when the Roman Catholic Church changed to regarding 29 February as the added day, but have not been able to find one. You never will find one, for one does not exist.

An article from the City Pulse is submitted as evidence. In it, a clueless journalist asks an equally clueless "calendar expert" about the evidence. To answer the question, does the expert whip out his Martyrology? His breviary? Any primary source whatsoever? Why no. He clicks on a website! He clicks on February 29th; it's blank. Therefore...

So much for the Catholic evidence. What about the Book of Common Prayer? What does it say? Why nothing at all. "It is implied..." quoth the footnote. In other words, the footnote author has original research to conclude that ordinals imply appending a day, rather than inserting a day, when ordinals imply nothing of the sort.

So the footnote is wrong and must be removed. What about the (now unsourced) statment which it is supporting? It also must be removed.

I'll get right on it. Rwflammang (talk) 00:18, 21 March 2015 (UTC)

I generally agree the information inserted by User:156.61.250.250, who is currently blocked, involves too much hand waving to satisfy me. However, when you (User:Rwflammang) reverted with no talk page discussion and terse edit summaries, I was left with the impression that you believed February 29 was the one and only leap day, ever since 1582.

There is at least one reliable source that states that both February 29 and February 24 (or perhaps February 25) has been used as the leap day at various times. Richards (1998, p. 100–101) states:

In the Christian calendar, 29 February is the intercalcated day in leap years. Leap years were so called because, as was written in the 1604 edition of the Anglican prare book, "On every fourth year, the Sunday Letter leapeth". The years which are not leap years are generally called "common" years....

There is a subtle difference between Anglican and Roman Catholic practices concerning the leap day. In the old Roman Julian calendar, that extra day was, as we have seen, inserted between the VII Kal. Mart. and the VI Kal. Mart.—that is, between 24 and 25 February. That practice was taken over by the Roman Catholic Church and continued by the English until 1662, when the extra day was moved to a place between 28 February and 1 March, and called 29 February. All this makes little discernible difference, except that in the Roman Catholic practice the Sunday, or dominical letter, is changed after 24 February rather than after 29 February. This can never affect the date of Easter but it does lead to celebrations of the feast of St. Matthias taking place on different dates in leap years in the two Churches.

As far as which is the intercalcated day for civil purposes, I think your reasoning for not considering the 366th day of the year to be the intercalcated day applies. American Independence day is celebrated on the 185th day of the year in common years, but 186th day of the year in leap years, so the intercalcated day must be before then. If we could find well-known public celebrations or deadlines in late February, and observe if they move or not, we could demonstrate which day is the civil intercalcated day. Or we could just take Richards' word for it. Jc3s5h (talk) 01:47, 21 March 2015 (UTC)

All of this information is a better fit for the leap day article. Here it clutters up this already over long article and distracts from its salient points. Rwflammang (talk) 17:52, 21 March 2015 (UTC)

It's ok to put the details in "Leap year" but the basic information about when the leap day occurs in this article, in part because it switched (for many purposes) from February 24 to February 29 around the same time the Gregorian calendar was adopted, so tends to be associated with the Gregorian calendar (although not a formal part of the change). Jc3s5h (talk) 12:33, 25 March 2015 (UTC)

Synthesis

I have reported this edit at WP:No original research/Noticeboard#Calendar synthesis?. Jc3s5h (talk) 15:49, 1 March 2015 (UTC)

7 months with 31 days, 4 with 30 and February's 28 (7x4) is an example of the GOD=7_4 algorithm/code

I added... The 7 months with 31 days, 4 with 30 and February's 28 (7x4) is an example of the GOD=7_4 algorithm/code.<ref http://GOD704.wikia.com</ref. For other patterns within the calendar consider Zeller's Congruence. 75.74.55.230 (talk) 05:13, 7 March 2015 (UTC)

Vernal equinox error

The "Accuracy" section is inaccurate. By definition, the position of the vernal equinox is arrived at after allowing for precession. The varying interval between astronomical vernal equinoxes is not caused by precession, it's caused by eastward movement of the perihelion relative to the stars. 156.61.250.250 (talk) 09:57, 10 March 2015 (UTC)

Using the Roman notation, the leap day is a.d. bis VI Kal. Mart. (24 February).

Is the sentence quoted above meaningful to anyone uninitiated to the arcana of the Roman calendar? If not, how does including it benefit the article? I will remove it. Rwflammang (talk) 00:25, 21 March 2015 (UTC)

Since you're arguing above that this is the leap day I would leave it, since it explains why. 87.81.147.76 (talk) 11:05, 21 March 2015 (UTC)

Let me heartily recommend removing both sentences from the article, since neither gives the article any benefit. Rwflammang (talk) 17:47, 21 March 2015 (UTC)

If Rwflammag just removes it, the article will say February 29 is the leap day, which Rwflammag disagrees with. I do think the passage should be revised to say that currently, February 24 is the leap day in the Roman Catholic Church but February 29 for civil purposes, rather than saying it depends on whether the date is written in Latin or English. Jc3s5h (talk) 13:04, 21 March 2015 (UTC)

Archiving

This page is currently automatically archived, I believe after 60 days. Automatic archiving is ridiculous for the level of traffic here. People will start discussing the same topic over again because they haven't seen the discussion which has been moved into the archive. If there are no objections I'll revert it to manual. 87.81.147.76 (talk) 18:10, 22 March 2015 (UTC)

I do not agree with you. Manual archiving is a bad idea, particularly as there is bad faith editing on this talk page. The IP address you are using has only been active for three months and you have only made two comments to this page neither of which have been archived. I presume that you have your own reasons for using an single issue IP account, however while you are using an IP account, while they are not blocked, you are of course free to add comments to this page and to the article, you are not to alter the archiving of this page, although you can ask others to do if for you. -- PBS (talk) 08:08, 24 March 2015 (UTC)

I checked the numbers: there is a throughput of about 20k over the last year so I have altered the archiving out to 365 days, on current through put that will expand the size of the page to about 30k with about 17 sections. If it proves to be much larger (either in size of sections) then it can be altered. -- PBS (talk) 08:31, 24 March 2015 (UTC)

Difference between Julian and Gregorian dates

In the third century the difference was zero. Thus H-(H/4)-2=2--2=2-0-2=0. In these equations the square brackets denote integer division.

In the second century the difference is -1. Thus 1--2=1-0-2=-1.

In the first century the difference is -2. Thus 0--2=0-0-2=-2.

In the first century BC the difference is -2. Thus -1--2=-1-(-1)-2=-2.

In the second century BC the difference is -3. Thus -2--2=-2-(-1)-2=-3.

In the third century BC the difference is -4. Thus -3--2=-3-(-1)-2=-4.

In the fourth century BC the difference is -5. Thus -4--2=-4-(-1)-2=-5.

In the fifth century BC the difference is -5. Thus -5--2=-5-(-2)-2=-5.

So the section was correct as written. You should put it back the way it was. 156.61.250.250 (talk) 13:10, 10 May 2015 (UTC)

It is perhaps less confusing if the mathematically equivalent relation D = floor(y/100) - floor(y/400) - 2 is used. Here y denotes the year and 'floor' denotes the floor or entier function. AstroLynx (talk) 13:50, 10 May 2015 (UTC)

The floor function gives a different result than truncation for negative numbers. I think it's better to use a relationship from a reliable source, so if the article is vandalized, an editor who does not want to rederive and retest the relationship can just restore the relationship from the cited source.

Let us postpone consideration of edge cases, after we agree on a correct formula for mid-century.

In the following table AYN means astronomical year numbering. The years assigned to centuries is common in offical sources but the Oxford English Dictionary said 2000 was the first year of the 3rd millenium. In ranges, the word "to" is inclusive, that is, "1 to 100" means 1 January AD 1 through 31 December AD 100. "Computed Secular Difference" is using the formula in the article which agrees with Blackburn and Holford-Strevens, using the value of H for mid-century to avoid edge cases (AD 250, AD 150, ... -550 BC).

The "Calendrica Secular Difference" was computed using the Calendrica LISP program provided by Cambridge University Press for use with Dershowitz and Reingold's book. Calendrica was used to convert Gregorian June 15 of the mid-century year to Julian and the difference is tabulated.

Jc3s5h (talk) 15:05, 10 May 2015 (UTC)

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