Talk:Gregorian calendar/Archive 5

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)
 * Red information icon with gradient background.svg 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. --John Maynard Friedman (talk) 12:04, 9 July 2021 (UTC)

Christian calendar
The Gregorian calendar as the Christian calendar is a huge misnomer. It is one of several Christian calendars, but is largely used more as a civil calendar throughout the world rather than an ecclesiastical calendar, although it can be referred to as one of several Christian calendars due to its propagation by the Catholic Church, invention or modification by a Catholic Pope, and adoption by many Western Christian denominations. 129.174.240.247 (talk) 05:22, 14 November 2021 (UTC)
 * Nowhere in the article does the phrase "Christian calendar" appear. Can you be more specific about which aspect of the article is of concern, bearing in mind the history of this calendar. By the way, the article does mention the Julian calendar (used in Eastern Christendom) and the notations Anno Domini (AD) and Common Era (CE). And Christian calendar is a wp:disambiguation article that lists four possible meanings of the term. --John Maynard Friedman (talk) 12:47, 14 November 2021 (UTC)
 * Until late last night (Nov. 13, 2021) or the early hours of this morning (Nov. 14, 2021), Christian calendar redirected to the Gregorian calendar until it was turned into a disambiguation page. 129.174.182.85 (talk) 16:36, 14 November 2021 (UTC)
 * Ah, so I see. Amazing that nobody noticed such blatant POV before. I'll put it on my watchlist in case someone reinstates the nonsense version. --John Maynard Friedman (talk) 17:52, 14 November 2021 (UTC)

Wiki Education Foundation-supported course assignment
This article is or was the subject of a Wiki Education Foundation-supported course assignment. Further details are available on the course page. Student editor(s): Abadams27.

Above undated message substituted from Template:Dashboard.wikiedu.org assignment by PrimeBOT (talk) 22:46, 16 January 2022 (UTC)

to rename "Polish" to "Polish–Lithuanian Commonwealth"
Between 1569-1795, the state is not called "Poland", but the "Polish-Lithuanian Commonwealth" had been named.

https://en.wikipedia.org/wiki/Polish%E2%80%93Lithuanian_Commonwealth — Preceding unsigned comment added by Ulti.paladin (talk • contribs) 18:47, 21 January 2022 (UTC)
 * ✅ --John Maynard Friedman (talk) 19:22, 21 January 2022 (UTC)

Need to reference true origins of calendar at the University of Salamanca in Spain
It should be duly noted that the Gregorian calendar was first created by scholars at the University of Salamanca in Spain. Omitting this important fact is historically misleading, and does not give credit to the people who really created it (vs the one who implemented it). 136.56.139.171 (talk) 04:39, 20 February 2022 (UTC)


 * What's your source for this claim? --  Jack of Oz   [pleasantries]  05:01, 20 February 2022 (UTC)

Semi-protected edit request on 11 September 2021
"In addition, the reform also altered the lunar cycle used by the Church to calculate the date for Easter, because astronomical new moons were occurring four days before the calculated dates."

Please look this paragraph over carefully. I believe it is being stated backwards. Days have to be added to the lunar calendar (8 in 2500 years). That means that the calendar new moons were coming sooner than the astronomical new moons and not the reverse. It can be confusing. Gal2man (talk) 23:46, 11 September 2021 (UTC)
 * This will need some thought and people familiar with the topic will probably contribute in a day or two. Meanwhile I have disabled the edit request because that is for simple and specified changes which do not require consideration. Johnuniq (talk) 02:31, 12 September 2021 (UTC)
 * We can check with the 2021 Julian Easter. The Golden Number of 2021 is 8, and from the table in, the Julian paschal full moon is Julian April 18. Which is Gregorian May 1 by adding the 13-day difference. (Searching the web verifies that Orthodox churches did celebrate Easter on the following Sunday, May 2 Gregorian.) Astronomically there was a full moon on April 26 (in my time zone), five days before the Julian paschal full moon. So the article is correct - "astronomical new moons were occurring four days before the calculated dates" in the 16th century, and often five days before in the 21st century. Indefatigable (talk) 19:15, 12 September 2021 (UTC)

Rather than using information from Wikipedia, I did a calculation for the paschal new moon for each year from 1570 to and including 1582, and 2021. I calculated the new moon using the Explanatory Supplement to the Ephemeris, the chapter "The Calendar", section E, "Ecclesiastical Calendars" (London: Her Majesty's Stationery Office, 1961). I obtained new moon information from the website of a retired NASA astronomer, Fred Espenak. (http://astropixels.com/ephemeris/phasescat/phases2001.html and related pages) I changed dates for 2021 to the Julian calendar. The times are UT, although one could argue Rome or Jerusalem would be better times to use.

Jc3s5h (talk) 16:27, 13 September 2021 (UTC)

One further point is that in times gone by, the new moon was considered to occur the first day the waxing crescent moon was visible. By modern standards, the moon is completely dark at the time of the new moon. So saying the astronomical new moon was about 4 days earlier than the ecclesiastical new moon is consistent with the older meaning of a new moon. Jc3s5h (talk) 18:21, 14 September 2021 (UTC)

Thank you Jc3s5h for your thoughtful reply. Calendar questions are sometimes confusing to me. I did an excercise to verify your proof and help clarify it for me.

Take the length of a metonic cycle = 6940 days and divide by 235. That gives an average lunation of 29.5319 days which is longer than the actual average synodical lunation of 29.53059 days. That would indeed make the astronomical phenomena occur before the ecclesiastical dates.

Thank you again! Gal2man (talk) 20:33, 16 September 2021 (UTC)

Thank you Jc3s5h for your thoughtful reply. Calendar questions are sometimes confusing to me. I did an excercise to verify your proof and help clarify it for me.

Take the length of a metonic cycle = 6940 days and divide by 235. That gives an average lunation of 29.5319 days which is longer than the actual average synodical lunation of 29.53059 days. That would indeed make the astronomical phenomena occur before the ecclesiastical dates.

Thank you again! Gal2man (talk) 20:34, 16 September 2021 (UTC)

A more accurate excercise would be to use (365.25x19) = 6939.75 6939.75÷235=29.53085 29.53059<29.53085 Same result: astronomical precedes ecclesiastical. Gal2man (talk) 23:27, 16 September 2021 (UTC)


 * I think the difference between the Gregorian and the Julian calendar should be 15 days rather than 13 days after year 2000, as the Gregorian calendar skips leap years during century years which are not multiples of 400. So, after the year 1500 it would have been leap year only in 400, 800 and 1200 which would give a difference of 12 days (15 minus 3) but now the calendar only moved forward ten days.

Besides that, a year is 365.2422 days to be more exact. To make it into 365.2422 days, a leap day should be added every year which is a multiple of 4 and not a century year + every year which is a quarter-millennium year (i.e. a multiple of 250) + every year which is a quarter-decamillennium year (i.e. a multiple of 2500); it would make the years 250, 750, 1250, 1750, 2250, 2500, 2750, 3250, 3750, 4250 and 4750 leap years = eleven "exceptional leap years" per half-decamillennium, which is exactly what should be needed to get an average year of 365.2422 days = 365 + 1211/5000. 213.65.211.63 (talk) 16:06, 9 March 2022 (UTC)

Gregorian Calendar.
Should the 0.0075 not be 0.75 in the following “ The Gregorian reform shortened the average (calendar) year by 0.0075 days to stop the drift of the calendar with respect to the equinoxes.”? 192.145.145.236 (talk) 09:59, 14 April 2022 (UTC)
 * The current value is correct. The change from Julian to Gregorian meant dropping 3 leap days over a 400-year period. 3/400 = 0.0075 days per year average. Favonian (talk) 10:37, 14 April 2022 (UTC)

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 — Preceding unsigned comment added by Timtempleton (talk • contribs) 22:58, 27 November 2017 (UTC)

Semi-protected edit request on 18 June 2022
Change Hegira to Hijrah اخسجہ (talk) 12:43, 18 June 2022 (UTC)


 * Comment: makes sense, given that the relevant article is Hijrah not Hegira. --John Maynard Friedman (talk) 12:56, 18 June 2022 (UTC)

✅ as has already been done for the other requests by same editor today.--John Maynard Friedman (talk) 20:47, 18 June 2022 (UTC)