Talk:Gregorian calendar

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RFC for help with Julian calendar conversion algorithm

There's a somewhat technical mathematical discussion at the Julian day article related to how algorithms convert Julian date to calendar date. I think some of the people watching this article might be able to contribute. Here's the specific RFC section: Talk:Julian_day#Request_For_Comment_on_presentation_of_algorithms

Semi-protected edit request on 3 June 2020

In the chart titled "Convertions from Julian to Gregorian dates", the "From" dates in the Julian column that start in February are 2 days too late for proper conversion as it would appear the author used a February with 30 days instead of 28.

Ex. In the second row the From Dates are: 1 March, 1700 (Gregorian) and 19 February, 1700 (Julian), however this only creates a difference of 9 days as February has 28 days not the 30 needed to have a difference of 11 days. Therefore the Gregorian From Date should be 3 March, 1700. 209.52.88.9 (talk) 12:26, 3 June 2020 (UTC)

The way the chart is to be used is to identify a Julian date to be converted, for example, 19 February 1700. See which row it falls into; it falls into the second row. Observe the difference is 11 days.

Recall that Thursday 4 October 1582 was followed by Friday 15 October 1582, so to find the Gregorian date one from the Julian date, one must count forward in the calendar 11 days:

1 20 Feb.

2 21 Feb.

3 22 Feb.

4 23 Feb.

5 24 Feb.

6 25 Feb.

7 26 Feb.

8 27 Feb.

9 28 Feb.

10 29 Feb. (1700 was a leap year in the Julian calendar)

11 1 Mar.

I am not happy with this table because long convoluted instructions are required to understand whether one should be counting on the Gregorian calendar or the Julian calendar, and such instructions are absent. Jc3s5h (talk) 13:57, 3 June 2020 (UTC)

Proposal to change the citation style slightly, to use template:sfn

Being conscious of WP:CITEVAR and MOS:RETAIN, I thought it best to seek consensus for a small change I would like to make to the citation style used at present in this article. The article currently uses 'naked' references like Richards 1998, p. 101. If reader mouses over the reference number in a sentence like Before the 1969 revision of the Roman Calendar, the Roman Catholic Church delayed February feasts after the 23rd by one day in leap years; Masses celebrated according to the previous calendar still reflect this delay., all that pops up from the reference number [1] is Richards 1998, p. 101.

My proposal is to change this type of reference to {{sfn|Richards|1998|page=101}}. The cited sentence will still look the same to visitors: Before the 1969 revision of the Roman Calendar, the Roman Catholic Church delayed February feasts after the 23rd by one day in leap years; Masses celebrated according to the previous calendar still reflect this delay. and on mouse-over the reference number [2] they will still see Richards 1998, p. 101 but if they hold the mouse over, the pop-up will expand to the full book citation, which to me is a lot more convenient, IMO.

References

Of course it will mean that I will have to reformat the sources to use {{cite book}}, so

• Richards, E. G. (2013). "Calendars". In S. E. Urban and P. K. Seidelmann (eds.), Explanatory Supplement to the Astronomical Almanac 3rd ed. (pp. 585–624). Mill Valley CA: University Science Books. ISBN 978-1-891389-85-6

will become

• Richards, E. G. (2013). "Calendars". In S. E. Urban; P. K. Seidelmann (eds.). Explanatory Supplement to the Astronomical Almanac (3rd ed.). Mill Valley CA: University Science Books. pp. 585–624. ISBN 978-1-891389-85-6.

Any objections? --John Maynard Friedman (talk) 11:47, 4 December 2020 (UTC)

It's OK with me. It looks like there is a book by Richards, and a book chapter by Richards. Also, some of these time & calendar related articles have references to different editions of the same book, so vigilance is needed. Jc3s5h (talk) 13:41, 4 December 2020 (UTC)

Book list

A big change so before I put it live, could someone check it please?

• Barsoum, Ignatius A. (2003). The Scattered Pearls. Piscataway: Georgias Press.
• Blackburn, Bonnie; Holford-Strevens, Leofranc (2003). The Oxford Companion to the Year: An exploration of calendar customs and time-reckoning (corrected reprinting of 1999 ed.). Oxford University Press. ISBN 9780192142313.
• Blegen, Carl W. (25 December 2013) [(n.d.)]. Vogeikoff-Brogan, Natalia (ed.). "An Odd Christmas". From the Archivist's Notebook. Retrieved 1 April 2018.
• Borkowski, K. M. (1991). "The tropical calendar and solar year". Royal Astronomical Soc. of Canada. 85 (3): 21–130. Bibcode:1991JRASC..85..121B.
• Carabias Torres, A. M (2012). Salamanca y la medida del tiempo (in Spanish). Salamanca: Ediciones Universidad de Salamanca.
• Coyne, G. V.; Hoskin, M. A.; Pedersen, O., eds. (1983). Gregorian Reform of the Calendar. Vatican Conference to Commemorate its 400th Anniversary, 1582–1982. Vatican City: Pontifical Academy of Sciences, Vatican Observatory (Pontificia Academia Scientarum, Specola Vaticana).
• Dershowitz, D.; Reingold, E. M (2008). Calendrical Calculations (3rd ed.). Cambridge: Cambridge University Press.
• Duncan, D. E (1999). Calendar: Humanity's Epic Struggle To Determine A True And Accurate Year. HarperCollins. ISBN 9780380793242.
• Gregory XIII (1582). Inter Gravissimas [Amongst the most serious tasks of our pastoral office]. Translated by Wikisource.
• Meeus, J.; Savoie, D. (1992). "The history of the tropical year". Journal of the British Astronomical Association. 102 (1): 40–42.
• Morrison, L. V.; Stephenson, F. R. (2004). "Historical values of the Earth's clock error ΔT and the calculation of eclipses". Journal for the History of Astronomy. 35, part 3 (120): 327–336.
• Moyer, Gordon (May 1982). "The Gregorian Calendar". Scientific American. Vol. 246, no. 5. pp. 144–152.
• Moyer, Gordon (1983). Coyne, G. V.; Hoskin, M. A.; Pedersen, O. (eds.). Aloisius Lilius and the Compendium Novae Rationis Restituendi Kalendarium. Gregorian Reform of the Calendar: Proceedings of the Vatican Conference to Commemorate its 400th Anniversary. Vatican City: Pontifical Academy of Sciences, Specolo Vaticano. pp. 171–188.
• Pattie, T.S. (1976). "An unexpected effect of the change in calendar in 1752" (PDF). British Library Journal.
• Pedersen, O (1983). Coyne, G. V.; Hoskin, M. A.; Pedersen, O. (eds.). The Ecclesiastical Calendar and the Life of the Church". Gregorian Reform of the Calendar: Proceedings of the Vatican Conference to Commemorate its 400th Anniversary. Vatican City: Pontifical Academy of Sciences, Specolo Vaticano. pp. 17–74.
• Richards, E. G. (1998). Mapping Time: The Calendar and its History. Oxford University Press.
• Richards, E. G. (2013). "Calendars". In Urban, S. E.; Seidelmann, P. K. (eds.). Explanatory Supplement to the Astronomical Almanac (3rd ed.). Mill Valley CA: University Science Books. pp. 585–624. ISBN 978-1-891389-85-6.
• Seidelmann, P. K., ed. (1992). Explanatory Supplement to the Astronomical Almanac (2nd ed.). Sausalito, CA: University Science Books.
• Swerdlow, N. M. (1986). "The Length of the Year in the Original Proposal for the Gregorian Calendar". Journal for the History of Astronomy. 17 (49): 109–118.
• Walker, G. W. (June 1945). "Easter Intervals". Popular Astronomy. Vol. 53, no. 6. pp. 162–178, 218–232.
• Ziggelaar, A. (1983). Coyne, G. V.; Hoskin, M. A.; Pedersen, O. (eds.). The Papal Bull of 1582 Promulgating a Reform of the Calendar. Gregorian Reform of the Calendar: Proceedings of the Vatican Conference to Commemorate its 400th Anniversary. Vatican City: Pontifical Academy of Sciences, Specolo Vaticano. pp. 201–239.

• I have copied this revision to live. --John Maynard Friedman (talk) 12:34, 16 December 2020 (UTC)

"Gregorian reform of the calendar" listed at Redirects for discussion

A discussion is taking place to address the redirect Gregorian reform of the calendar. The discussion will occur at Wikipedia:Redirects for discussion/Log/2020 December 15#Gregorian reform of the calendar until a consensus is reached, and readers of this page are welcome to contribute to the discussion. Soumya-8974 (he) ^talk _contribs ^subpages 17:40, 15 December 2020 (UTC)

"Gregorian calendar reform" listed at Redirects for discussion

A discussion is taking place to address the redirect Gregorian calendar reform. The discussion will occur at Wikipedia:Redirects for discussion/Log/2020 December 15#Gregorian calendar reform until a consensus is reached, and readers of this page are welcome to contribute to the discussion. Soumya-8974 (he) ^talk _contribs ^subpages 17:40, 15 December 2020 (UTC)

"15 October 1582" listed at Redirects for discussion

A discussion is taking place to address the redirect 15 October 1582. The discussion will occur at Wikipedia:Redirects for discussion/Log/2020 December 15#15 October 1582 until a consensus is reached, and readers of this page are welcome to contribute to the discussion. Soumya-8974 (he) ^talk _contribs ^subpages 17:40, 15 December 2020 (UTC)

Book list markup

@John Maynard Friedman:. Your recent edits suggest you think the following would not work: Scientific American is a great magazine.{{sfn | Moyer | 1982}}

{{cite magazine|author-last1=Moyer |author-first1= Gordon | issue= 5 | volume = 246|date = May 1982 | title= The Gregorian Calendar | magazine=Scientific American | pages=144–152}}

But it does work. The templates are able to extract the 1982 from the date and match it up with the 1982 from the sfn template. Jc3s5h (talk) 19:18, 15 December 2020 (UTC)

Thanks, that's good news. I couldn't find anything at {{sfn}} or {{cite}} to say it did so I didn't bother to try. Oh me of little faith. I will change it back. Did you have time to check any others? One item that worried me is that Worldcat is giving the same ISBN for all editions of the The Oxford companion to the year, but I suppose the change from ISBN-10 to ISBN-13 just exposed a pre-existing issue, it didn't create it. --John Maynard Friedman (talk) 19:36, 15 December 2020 (UTC)

 Done --John Maynard Friedman (talk) 12:40, 16 December 2020 (UTC)

I checked the following book, which I own:

Cite book comparison

Wikitext	{{cite book|author-first1=Bonnie|author-first2=Leofranc|author-last1=Blackburn|author-last2=Holford-Strevens|isbn=9780192142313|publisher=Oxford University Press|title=The Oxford Companion to the Year|year=1999}}
Live	Blackburn, Bonnie; Holford-Strevens, Leofranc (1999). The Oxford Companion to the Year. Oxford University Press. ISBN 9780192142313.

.

I checked that it sort of supports all the claims in the article, more on that later. The one I have was reprinted with corrections in 2003, so I would write the citation thus

Cite book comparison

Wikitext	{{cite book|author-first1=Bonnie|author-first2=Leofranc|author-last1=Blackburn|author-last2=Holford-Strevens|edition=corrected reprinting of 1999|isbn=9780192142313|publisher=Oxford University Press|title=The Oxford Companion to the Year|year=2003}}
Live	Blackburn, Bonnie; Holford-Strevens, Leofranc (2003). The Oxford Companion to the Year (corrected reprinting of 1999 ed.). Oxford University Press. ISBN 9780192142313.

.

World cat seems to say that ISBN goes with the 2003 corrected reprinting, and agrees with what is printed on page iv of mine.

In the article, the whole section "Difference between Gregorian and Julian calendar dates" is suspect because it describes one calculation, but supports it with more than one source (one of them is Blackburn & Holford-Strevens); who is to say the calculations in the two sources are compatible? The section extends the calculation before AD 1, but the book only gives dates in the 2nd and 3rd millennium as examples. Jc3s5h (talk) 20:37, 15 December 2020 (UTC)

 Done , though not identically. --John Maynard Friedman (talk) 12:40, 16 December 2020 (UTC)

I want to stick with tunnel vision for the moment, and just update the citation style. The question you raise is a valid one but best I leave it to you to resolve. (I have doubts about extending the proleptic Gregorian before 325 but I definitely think that we should not facilitate extension before the epoch, that way madness lies. --John Maynard Friedman (talk) 21:01, 15 December 2020 (UTC)

I have copied the list to live. Feel free to just revert if you see anything that needs further correcting because the version above is up to date and can more easily be revised and recopied to live when done. --John Maynard Friedman (talk) 12:40, 16 December 2020 (UTC)

Conversion from Julian to Gregorian dates

Jc3s5h
Your table is not compatible with the table in the reference: Conversion between Julian and Gregorian calendars. sigurdhu (talk) 10:54, 13 January 2021 (UTC)

It's not my table. I'm not a big fan of it. But your change did not accurately reflect page 417 from the Explanatory Supplement to the Ephemeris (1961). Jc3s5h (talk) 18:41, 13 January 2021 (UTC)

error in describing the difference between Julian and Gregorian calendars

There is an error in the following sentence in the Description paragraph: The only difference is that there is one day less in the leap month (February) every four hundred years.

In fact, in the Gregorian calendar there is one less day in the leap month once every century except in centuries divisible by 400. So, I propose the above sentence from the Description is changed to: The only difference is that there is one day less in the leap month (February) once each century except in centuries divisible by four (e.g. 1600, 2000) which retain their leap day. — Preceding unsigned comment added by Patrickanderson (talk • contribs) 06:00, 10 February 2021 (UTC)

Should AD be replaced with CE in this article?

When I see AD (Anno Domini) be used in most historical articles I usually change it to CE, (Common Era) as CE is more inclusive and accurate. However, I'm not sure whether this applies here, seeing as the calendar was originally created using AD. Any opinions on this? — Preceding unsigned comment added by Maxi25554 (talk • contribs) 02:21, 3 March 2021 (UTC)

No. The AD notation is associated with Christianity, the process that lead to the calendar was started by Pope Gregory XIII, and he ordered the Catholic Church to adopt the calendar. Jc3s5h (talk) 04:00, 3 March 2021 (UTC)

In Wikipedia, the MOS:ERA policy says that either style is valid BUT the style first used in the article should be retained unless there is a consensus that the 'wrong' one has been used – for example using AD in an article about Judaism or Islam, using CE in an article about Christianity. So there is zero prospect of the era style in this article being changed, for the reason that Jc3s5h gives and more. If you create a new article, you may use CE but you must not unilaterally change the era of any existing article. In practice, this policy has been invoked rather more often to prevent articles that began as CE being changed to AD than the other way round. --John Maynard Friedman (talk) 16:26, 3 March 2021 (UTC)

Semi-protected edit request on 10 April 2021

In "Description" the sentence "The only difference is that there is one day less in the leap month (February) every four hundred years". It should say three days less every four hundred years instead of one day. The error was introduced by User:Enthusiast01 in the changes he did in 25 December when he replaced the original "The Gregorian reform omitted a leap day in three of every 400 years and left the leap day unchanged." Psxlover (talk) 19:52, 10 April 2021 (UTC)

Thank you for the prompt and the chance to comment. On a re-reading of the quote of the United States Naval Observatory at beginning of article, three leap day in every 400 years are not to be treated as a leap year. My mistake. I will correct it. Enthusiast01 (talk) 22:09, 10 April 2021 (UTC)

Proleptic before 1582?

We say: The Gregorian calendar is proleptic before 1582 (calculated backwards on the same basis, for years before 1582), ...

I guess I can imagine some abstruse scientific contexts in which it's important to know what the Gregorian date would have been, for events prior to 1582, had the Gregorian calendar been introduced earlier than it actually was. But for general purposes the Julian calendar ended on 4 October 1582 (OS), and the Gregorian came into existence the next day, 15 October 1582 (NS), and to talk about Gregorian dates prior to then is pretty meaningless, because we only ever use Julian dates for pre-1582 events. So, in what sense is it proleptic? -- Jack of Oz ^{[pleasantries]} 08:11, 22 June 2021 (UTC)

A date format that you may see sometimes is 2021-06-22. This format is specified by a standard published by the International Standards Organization, ISO 8601. (Some people may be using this format without ever having heard of ISO 8601). The standard specifies, among other things, that it always uses the Gregorian calendar. So if someone were to write 1500-01-01, and assert that it is written in the ISO 8601 format, they would be asserting that it is a proleptic Gregorian date.

However, because the Gregorian-only requirement is not widely known, I wouldn't be surprised if most of the pre-1582 dates that purport to be in the ISO 8601 format are really Julian dates. Jc3s5h (talk) 11:24, 22 June 2021 (UTC)

Law of unintended consequences: I suspect the ISO committee just wanted to rule out 1500 AM, 1500 AH etc when they specifed Gregorian-only? --John Maynard Friedman (talk) 18:34, 22 June 2021 (UTC)

I am not aware of any record of there discussions. Who knows what they were thinking. My suspicion is they were a bunch of computer nerds focused on things like airline tickets and pay checks. I the first version they even allowed two digit years (e.g. 92 for 1992). If they couldn't think ahead a decade, I strongly suspect they had no idea that there were (and are) people alive who's birth date on their birth certificate was written in the Julian calendar. Jc3s5h (talk) 14:49, 24 June 2021 (UTC)

Semi-protected edit request on 3 July 2021

You should mention it was invented in the University of Salamanca in 1515, there's not a single mention of this in the whole article.176.87.9.128 (talk) 02:46, 3 July 2021 (UTC)

 Not done: please provide reliable sources that support the change you want to be made. ◢  Ganbaruby!  (talk) 05:19, 3 July 2021 (UTC)

Apologies, this is the source: Carabias Torres, Ana María (2012). Salamanca y la medida del tiempo. Ediciones Universidad de Salamanca. ISBN 978-84-9012-076-7.

The proposal from Salamanca is already in the article, under Gregorian calendar#Background. --John Maynard Friedman (talk) 12:04, 9 July 2021 (UTC)

IMPORTANT

Why is there a 7-year gap with all years having only 365 days each?

Why is there no leading zero if the numbers beyond 9 have two digits?

I noticed that there are only nine numbers with a leading zero or with only one digit. Example: 2021-08-31 comes before 2021-09-01 instead of 2021-09-00.

February has only 28 days, two days below the average. Look at the chart below.

NOT AVERAGE-|-AVERAGE----|-DIFFERENCE

31----------|-30.4-------|-0.5

59----------|-60.8-------|-1.8

90----------|-91.2-------|-1.2

120---------|-121.6------|-1.6

151---------|-152.0------|-1.0

181---------|-182.5------|-1.5

212---------|-212.9------|-0.9

243---------|-243.3------|-0.3

273---------|-273.7------|-0.7

304---------|-304.1------|-0.1

334---------|-334.5------|-0.5

You have to understand all the information above. 111.68.55.247 (talk) 04:31, 8 September 2021 (UTC)