Talk:Proleptic Gregorian calendar

message: The Julian calender wasn't in use from AD 4 but 45 BC! Rich Farmbrough 08:50, 24 Jun 2005 (UTC)
replies: text: The last paragraph could be worded a little better. But the Julian calendar that we are familiar with did not begin until AD 4. The Julian calendar that began 45 BC had a leap year every three years instead of a quadrennial leap year. In 8 BC, Caesar Augustus removed the excessive leap years by not allowing any more leap years until AD 4, which was the first leap year of the medieval Julian calendar. See Julian calendar for all the details, especially leap years error. — Joe Kress 02:57, 25 Jun 2005 (UTC)
thread_title: AD 4 vs 45 BC

message: Astronomers usually note years before 1 A.D. by negative numbers (e.g. the year -4 etc.), not by use of "B.C.", so there's not all that much chance of confusion... AnonMoos 13:01, 24 September 2006 (UTC)
replies: text: On the contrary, several modern historians use negative numbers for years BC, but their negative years differ by one year from the astronomer's year because these historians do not use a year zero, placing −1 immediately before 1, creating endless confusion. — Joe Kress 19:23, 25 September 2006 (UTC)
thread_title: Astronomical vs. ordinary year notation

message: I object to the merge of most of the section Gregorian calendar#Proleptic Gregorian calendar into this article, especially those paragraphs, which comprise most of it, which discuss dates after 1582. Although I don't necessarily object to merging the remainder of the section discussing years before 1582, because that would leave only one small paragraph, I think any merger is useless. — Joe Kress 23:01, 18 November 2006 (UTC)
thread_title: Merge

message: When ancient dates from times before the introduction of the Julian calendar are given, e.g. the foundaition of the Japanese Empire on February 11 660 B.C. or the Battle of Cannae on August 2 216 B.C. which prolepic calendar is used, the Gregorian or the Julian one?  —Preceding unsigned comment added by 91.62.112.219 (talk) 12:19, 17 June 2009 (UTC)
thread_title: Ancient dates

message: It would be useful if this article had a special section that explained how leap years are defined for year zero and BC years. Most people say that a year in the Gregorian calendar is a leap year if and only if the year is "divisable by 4 but not divisable 100 except if it's divisable by 400". But 0 is kind of divisable by any integer so?? Also, in Bede's proleptic calendar there was no actual year zero so does that means year 1 BC was a leap year?
-- mnemo (talk) 11:22, 30 December 2009 (UTC)
replies: text: After reading more carefully, I suppose it's sort of covered already... --mnemo (talk) 11:26, 30 December 2009 (UTC)
thread_title:  Leap years? 

message: I believe the table is not appropriate for this article, calendar conversion is a subject of it's own. If there is a desire for a good manual method of conversion, I am prepared to enter the table from the Explanatory Supplement to the Astronomical Ephemeris and the American Ephemeris and Nautical Almanac (1961), under an appropriate title.
All that is left is the fact that the proleptic Gregorian calendar exists, and the leap year rules requested by Mnemo above. I think it would be best to merge that into Gregorian calendar and make this a redirect. --Jc3s5h (talk) 23:07, 19 January 2010 (UTC)
thread_title: Redirect

message: Contains "dates preceding its official introduction in 1582".  That could mislead; the Papal authority was of limited extent and effect.  Remove "official" or replace it with "first", I suggest. 82.163.24.100 (talk) 20:45, 12 October 2010 (UTC)
replies: text: I see no problem with "official" for the same reason you cite for its removal—"official" is understood to be limited by the authority promulgating it. Nevertheless, I would agree to changing the phrase to "dates preceding its introduction by the Roman Catholic Church in 1582." "First" duplicates "introduction". — Joe Kress (talk) 07:55, 14 October 2010 (UTC)
thread_title:  Introduction 

message: Holocene calendar Conversion says:
:Conversion to the Holocene Era from Julian or Gregorian AD years can be achieved by adding 10,000. BC years are converted by subtracting the BC year from 10,001.
:A useful validity check is that the last single digits of BC and HE equivalent pairs must add up to 1 or 11.''
Is it just me, or does that really not make sense? I'd like to know if calculating the day of the week for 1 January 1 HE yields a Monday, and how to calculate where it fell in relation to mid-winter. --Pawyilee (talk)
:Neither the day of the week nor the season is mentioned in the Holocene calendar. Both are dependent on the calendar chosen, Julian or Gregorian, both of which have been assumed. Using Calendrica, in the Julian calendar, 1 January 10000 BC (1 HE) is a Monday with a solar position of 211°, about 30° or one month after the autumnal equinox at 180°. In the Gregorian calendar, 1 January 10000 BC (−9999) is also a Monday but with a solar position of 285°, half a month after the winter solstice at 270°. Because both are a Monday, the difference between the Julian and Gregorian calendars in that year is a whole number of weeks, 77 days or 11 weeks, obtained by subtracting the two Julian days also provided. 
:Regarding the digit relationship, note that the first 10000 Holocene years are simply the corresponding BC years numbered backwards, 1–10000 HE = 10000–1 BC. The pair of least significant digits cycles through 1+0=1, 2+9=11, 3+8=11, 4+7=11, 5+6=11, 6+5=11, 7+4=11, 8+3=11, 9+2=11, 0+1=1, etc. — Joe Kress (talk) 03:50, 16 October 2010 (UTC)
replies: text: Thanks! Please consider pasting what you wrote about Calendrica to the Holocene calendar Conversion! (
I won't do it lest it break some convention of which I'm ignorant.) --Pawyilee (talk) 13:43, 16 October 2010 (UTC)
thread_title: Prolepti-plasm

message: The last entry of this table for the Proleptic Gregorian range is :
"From 11 March 1500 to 4 October 1582"
This is wrong, because 4 October 1582 was the last day of the julian calendar which corresponded to 14 October 1582 in the proleptic gregorian calendar. The last 10 days are missing. So the last line of this table should be:
Julian range                        	Proleptic Gregorian range             	Gregorian ahead by:
From 1 March 1500  to 4 October 1582	From 11 March 1500  to 14 October 1582	10 days
Japf (talk) 19:09, 14 April 2012 (UTC)
thread_title: Table of correspondence between calendars

message: As there are 'a number of communities' which still use the Julian calendar - is there an equivalent term for converting Gregorian dates to the Julian ones? (Mount Athos is probably the most well known; and Tsarist-period Russia - hence the October Revolution being celebrated in November... and there was a possibly urban legend about some Russian athletes arriving at an Olympics late having used the Julian calendar) 80.254.147.68 (talk) 14:16, 11 April 2013 (UTC)
thread_title: Julian calendar extended

message: The sentence 'the number of days that the calendars differ is undefined for few days.' doesn't seem quite right. Although within the context I'm not 100% sure of the correction. SamCardioNgo (talk) 08:31, 24 October 2012 (UTC)
replies: text: That sentence is severely messed up. Before the introduction of the Gregorian calendar there was no proleptic Gregorian calendar and certainly no difference. There aren't any undefined differences between the calendars. I don't know what the author meant but what he wrote is incomprehensible and wrong.  Senor Cuete (talk) 13:43, 24 October 2012 (UTC)
replies: text: The way I read it, for a leap year, you can number the days from 1 to 365, or for a leap year, you can number the days from 1 to 366. The days are also named starting with January 1 and ending with December 31. If you are comparing a Gregorian common year to a Julian common year, or a Gregorian leap year to a Julian leap year, you can find the number that corresponds to the day name, subtract the numbers, and find the difference (you have to define a convention to determine whether the difference is considered positive or negative). But if you are comparing a Gregorian common year to a Julian leap year, it isn't obvious whether to look up the number of the day name on the list with 365 entries, or 366 entries. Since the article does not define a convention describing what to do, the difference is undefined. Jc3s5h (talk) 16:54, 24 October 2012 (UTC)
replies: text: I'd say there are two things, the meaning, and the grammar. Surely there's a way to improve the latter at least? SamCardioNgo (talk) 11:15, 25 October 2012 (UTC)

text: No day is undefined. The way to convert to/from the proleptic Gregorian calendar is to convert to/from a Julian day number.  Senor Cuete (talk) 15:08, 25 October 2012 (UTC)
replies: text: It's true that any Julian calendar date after AD 8 can be converted to a (proleptic) Gregorian calendar date, and vice versa. (In and before AD 8 there is some uncertainty about how the Romans actually implemented their calendar; it is known they didn't follow Julius Caesar's rules exactly.) One could say the difference between January 14, 2011 Gregorian and January 1, 2011 Julian is 0, because they are the same day. But some people who convert between the calendars don't want to convert to Julian Day Numbers as an intermediate stage and want to convert directly, so those people would say the difference is ± 13. Jc3s5h (talk) 16:00, 25 October 2012 (UTC)

text: True and they can do it by using the table that gives the difference between the calendars. What does this have to do with the strange incomprehensible (except to you?) text in question?  Senor Cuete (talk) 16:37, 25 October 2012 (UTC)
replies: text: I don't claim the text is well-written. I'm just pointing out some related concepts; if someone want's to rewrite the text they should clearly distinguish their meaning of "difference" from other possible meanings. The table provided does not permit the conversion of certain dates, such as March 1 & 2, AD 500 Gregorian, because they are absent from the table. Jc3s5h (talk) 16:46, 25 October 2012 (UTC)
replies: text: It's getting hard to count the colons;) But I think I might have a suggestion that we could at least discuss. My suggestion relates to one emendation (which is in square brackets), I've added the full paragraph here for context -> 'Whenever the calendars do not have corresponding days — **example given**   — the number of days that the calendars differ is undefined for [those] days.' So only word that needs to be changed is [few], which, on the original, sits where [those] now resides. Any thoughts?SamCardioNgo (talk) 18:18, 25 October 2012 (UTC)
replies: text: The only thing that is undefined is how this confusion appeared.  Jc3s5h says that March 1 & 2, AD 500 PROLEPTIC Gregorian is not defined, because they are absent from the table. My question is why? It is obvious that those days correspond to February 28 and 29, 500 in the Julian calendar. What is really undefined is the difference between calendars.To solve this problem, we only need to know the context. It seems to me that the table gives how many days we add to the Julian Calendar (that was effectively in use) to obtain a proleptic Gregorian date. If we take 27/2/500J that corresponds to 28/2/500G the difference is obviously 1. The next day is 28/2/500J and 1/3/500G. The difference is now 2 in Julian Calendar and will continue to be 2 until the year 600. You can say that for this day the difference is still 1 if we depart from the Gregorian calendar, but that is not the aim of the table - as I said above this table serves to convert julian in proleptic gregorian and not the way round. So the sentence is nonsense and the table should be completed with the missing days.Japf (talk) 19:46, 26 December 2012 (UTC)

text: I disagree. "Gregorian ahead" means "in comparison to the julian calendar" so there is no ambiguity. Nevertheless, you can complete the table with all the dates, and add a footnote saying that the date difference may depend in some dates if we are counting the days in the gregorian or in the julian calendar. nThe present table say that we can't stablish a correspondence between 28/2/500J and 1/3/500G, and that is wrong.Japf (talk) 02:29, 27 December 2012 (UTC)
replies: text: I disagree with "The present table say that we can't stablish a correspondence between 28/2/500J and 1/3/500G, and that is wrong." The present table does not state which Gregorian date corresponds to 28 February 500, but it does not state that the equivalent date is unknown. The problem is that not enough rules are stated to say whether conversion between 28 February 500 Julian and 1 March 500 should be done by counting forward 2 dates on a date list that includes 29 February, or forward 1 date on a list that omits 29 February. Jc3s5h (talk) 01:15, 28 December 2012 (UTC)
replies: text: And if we put a fotenote stating "The values shown in the column Gregorian ahead mean days added to the date in the Julian Calendar". Anything must be done because the table can't remain with undefined dates like it is now.Japf (talk) 15:48, 31 December 2012 (UTC)
replies: text: Dates are not added, they are converted. The method of conversion must be stated unambiguously. Jc3s5h (talk) 00:31, 1 January 2013 (UTC)
replies: text:  What do you think about a footnote stanting "without counting the February 29 of the julian calendar". A compromise solution must be found. The present table is inacurrated.Japf (talk) 17:10, 1 January 2013 (UTC)
replies: text:  Yes it's a good idea (also equivalent to counting days in the Gregorian Calendar). Karl (talk) 13:11, 3 January 2013 (UTC)
thread_title:  Undefined for few days 

message: I noticed that, for the period from 1 March 300 to 28 February 500, there is a difference of one day between the two calendars. As this period includes the First Council of Nicaea, to which the Gregorian count of days was supposed to revert to (regarding calculations of the date of Easter), surely there shouldn't be any difference at all? Or was the calendar inaccurately adjusted? Chaotic Enby (talk) 09:06, 19 April 2023 (UTC)
replies: text: From what I've read, there was a general goal to restore the March equinox to, on average, March 21, which the reformers believed was the average March equinox at the time of the First Council of Nicaea. I've never seen any mention of the reformers thinking about a proleptic Gregorian calendar or how it would compare to the Julian calendar. Jc3s5h (talk) 12:15, 19 April 2023 (UTC)
replies: text: They probably didn't think of it in these terms, but if they wanted to put the Gregorian calendar back in sync with the time at the First Council of Nicaea, it would be equivalent with having the proleptic calendar sync back with the Julian calendar at that date, right? Is there something I'm not seeing, or is there actually a one-day mistake that hasn't been commented on yet? Chaotic Enby (talk) 13:48, 20 April 2023 (UTC)
replies: text: This is discussed extensively in Gregorian Reform of the Calendar:Proceedings of the Vatican Conference to Commemorate its 400th anniversary 1582 - 1982. In particular see the chapter "The Papal Bull of 1582 Promulgating a Reform of the Calendar" by August Ziggelaar, starting on page 201 (as printed in the text, not as shown in the PDF page count). In summary, it was known that the traditional method of calculating Easter, as implemented by Dionysius Exiguus, treated March 21 as the date of the March equinox. The goal was to restore the average date of the March equinox to March 21. The correct way to judge whether the reformers made an error would be to calculate the average date of the March equinox near 1583 and see if it's March 21. Whether or not the difference between the Julian calendar and the Gregorian calendar was 0 days in 325 was not a criterion of the correctness of the reform. Jc3s5h (talk) 15:39, 20 April 2023 (UTC)
thread_title:  Accuracy of the table? 

message: The article mentions that Roger Bacon estimated the inaccuracies of the calendar system during his time "c. 1200", when he wasn't even born until c. 1219. Perhaps change "c. 1200" to say "in the 13th century" in a similar fashion to how Bede's contributions are mentioned? Geographynerd101 (talk) 12:42, 22 May 2023 (UTC)
thread_title:  Date of Roger Bacon’s Calculations