Talk:Proleptic Gregorian calendar

AD 4 vs 45 BC

The Julian calender wasn't in use from AD 4 but 45 BC! Rich Farmbrough 08:50, 24 Jun 2005 (UTC)

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)

Astronomical vs. ordinary year notation

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)

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)

Merge

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)

Explicitly not-proleptic

"Explicitly not-proleptic" would mean that the Roman Catholic Church explicitly stated that its new calendar could not be used for dates before its official introduction in 1582. But no such statement appears in the papal bull Inter gravissimas which promulgated it.

I have no objection to providing examples of current usage provided they are correct. Of the three examples given, only the first is correct—the last two are not. I considered simply correcting them, but instead decided to discuss them first.

• The matryology example only gives the current practice of the Roman Catholic Church. It does not prevent those outside the Church from using the Gregorian calendar in other ways. Early Christian dates are so confused that Protestants notoriously disagree on any such date. Although most Julian dates are given the same name in the Gregorian calendar, both within and outside the Church, sometimes people convert them into the proleptic Gregorian calendar to find the nominal anniversary date.
• The astronomical example distorts the practice of astronomers, which use neither the Julian calendar nor the Gregorian calendar when calculating dates. Instead they use the 'Julian date', which does not mean a date in the Julian calendar but instead means a day and a fraction thereof in a continuous sequence of days from a date in the remote past. The Julian date as I write this is 2454205.48333, given to a precision of about one second. Sometimes such a Julian date is used as is without any conversion, but usually it is often converted into the appropriate calendar date and time, Gregorian after 1582 and Julian before 1582. Another astronomical practice can also be confusing—the use of Julian centuries and millennia. Again, this does not mean that the Julian calendar is used, instead a Julian century means a period of 36525 days and a Julian millennia means 365250 days is applied as an offset to some 'Julian date'. Either can indicate a period before or after any date, although in modern astronomical practice the Julian epoch J2000.0 is usually used, which is the Julian date 2451545.00000, or the Gregorian calendar date noon 1 January 2000 (neither the equivalent Julian calendar date of noon 19 December 1999 nor the Julian calendar date of noon 1 January 2000 is ever used). It would be better to simply say that astronomers do not use the proleptic Gregorian calendar.
• The Julius Caesar example is confused and a poor example unless you want to get into a long discussion of the proleptic Julian calendar. Roman sources state that Julius Caesar was assassinated on the Ides of March in the year when Julius Caesar was consul for the fifth time and Mark Antony was consul for the first time. A simple translation, not a conversion, of this is 15 March 44 BC. But during its first few decades the Julian calendar added an intercalary day every three years instead of every four years, so this date in the proleptic Julian calendar, which adds an intercalary day every four years without exception, is 14 March 44 BC. The equivalent of the nominal date in the proleptic Gregorian calendar is 13 March 44 BC, whereas the equivalent true date in the proleptic Gregorian calendar is 12 March 44 BC. In no case does the proleptic Gregorian calendar ever change the year—it is always 44 BC. In astronomical year numbering, 44 BC is written as −43 in both the Julian and Gregorian calendars because of the year 0. It is not now written as 43 BC (early French astronomers around 1700 would have said 43 BC, because they did not use negative years). A better example for you would be the coronation of Charlemagne as emperor on Chrismas Day 25 December 800, because Anno Domini years were actually used in 800 and it is well after the early confused period of the Julian calendar. Historians would not convert this using the proleptic Gregorian calendar into 29 December 800.

I have never heard of an English word tardif, and it does not appear in the Oxford English Dictionary. Nevertheless, I understand your desire to mention the use of the proleptic Gregorian calendar between 1582 and 1752 or some other year when a country adopted the Gregorian calendar. However, whether dates within that interval are converted or not is country dependent. It is normal to convert United States dates but not British dates. But that is not always the case among historians. George Washington's birth is sometimes given as 11 February both because that is the date in his family bible and because Washington himself celebrated his birthday on 11 February, even though he magnanimously accepted Happy Birthday wishes from others who insisted that it be celebrated on 22 February during his lifetime. If George Washington is given as an example then say usually. — Joe Kress 02:07, 15 April 2007 (UTC)

You are right. Myself, just before I stored my changes, I hesited: "explicitly" ?  Of course this would mean: expressed in a statement. However the Commemoration Day decision made it clear, without any doubt. Rome, in 1582, assumed the previous error of the Julian Calendar. In the Catholic calendar, the days between October 4th and 15th don't exist. So, there is no "proleptic Gregorian Calendar" recognized by Roman Church. That's a fact.  –  Merely, the word "explicitly" is probably not-adequate.

• "[This do] not prevent those outside the Church from using the Gregorian calendar in other ways."

Ha, you are right! Since Gregorian Calendar isn't "patent-protected", who wants, can manage his own changements, in various sorts of 'modified Gregorian Calendars'.
This is even necessary. Since currently, G.C. is also the 'world-wide civil calendar', at least, all the Christian matryology Days don't be recognized by the civil society.
Similary, Cassini modified the Christian Era by the astronomical year numbering.

The question is: "What's the current practice?" and "Who recognizes which calendar variant?"

"... both within and outside the Church, sometimes people convert them into the proleptic Gregorian calendar to find the nominal anniversary date."
This, Joe, is your own, pure speculation, supported by nothing. I contest it.

• If the astronomers (still) use the Julian Date  (and the Julian centuries, instead of the progressive von Mädler periods of 46 751 days),  this means that they still use the Julian calendar.
  However we agree: "Astronomers do not use the proleptic Gregorian calendar."
  Therefor, the additional reason is, that the unequal gregorian centuries are unadapted for astronomical calculations.

• Concerning your remarks concerning the date of Caesar's death:  May be a simplified example, a not-exhaustively developed one, but not a 'poor example'.
  

"In no case does the proleptic Gregorian calendar ever change the year." Since ISO8601 promotes p.G.C. and since there is also a year zero in ISO8601, it well changes the year. But we can agree that the writing AD –43 is clearer, better. Also for the rest, we don't disagree w.r.t your statements on this topic.

Remains the most important question:  "Who really uses the so-called proleptic Gregorian calendar and ISO8601?" (exepting 'most Maya scolars')

I would say:  No one !, and this for good reasons.
 :The simple truth is: "Nobody can try to implement successfully any proleptic calendar by keeping the previous Era!"
This would be source of bedevilment, a vile confusion. All historians will refuse, forevermore. (Gregory XIII knew it, so he didn't try it.)

The imbroglio caused by the belated adoption of Gregorian Calendar by non-catholic countries is great enough. (cf. days of death of Cervantes and Shakespeare)

I resume. This so-called p.G.C. and its ISO8601 (not in all its parts) is inconsistent, a pseudo-newfangled cul-de-sac, a dead-end way.

By changing era, the proleptic rule becomes possible.

Then one can try to examinate whether and how "idibus Martias 710 a.u.c." is affected by the well-known Roman confusion concerning the leap years, in principle, cleared by Augustus. One can try to see if it is possible to determinate, that corresponds to the 12th, 13th day of the third month of the year... (Like this is already proposed. Caesar's death on:) CE -1835.

-- James175 12:01, 15 April 2007 (UTC)

PS.  Dates between 1582–1752: the US-american historian-use is progressive, not so GB-use.* – G.W. was right. That's a good opportunity to celebrate his anniversary twice ;-) once personally, in family, the second time officially.
 * Here, the best use should be the double indication: N.S. (O.S.). At least as long as one stays is AD, if not: new CE (AD O.S.).

A well known example of a Christian Julian anniversary being celebrated on its equivalent Gregorian date is the Russian Christmas, which is 25 December in the Julian calendar but is always celebrated on 7 January in the Gregorian calendar used throughout Russia. A similar example is Orthodox Easter—although it occurs between 22 March and 25 April in the Julian calendar, it is celebrated between 4 April and 8 May in the Gregorian calendar used in every Orthodox country. Another well-known example of the use of the proleptic Gregorian calendar for an anniversary is the October Revolution of the Soviet Union, which was always celebrated in the Gregorian November. Some computer languages assume that all dates are Gregorian, whether they are before 1582 or not, such as javascript. The Christian Aristeo Fernando regulary uses the proleptic Gregorian calendar for his Christan dates, even though they differ greatly from the traditional dates.

Just because both the astronomical Julian date and Julian centuries were originally named after Julius Caesar does not mean that the like-named Julian calendar is used—it is not. Astronomers want to determine the period of time that has elapsed between two astronomical events. For this purpose, Julian calendar dates are never used, nor are Gregorian calendar dates. Calendar dates are always converted into the astronomical Julian date, a count of days, before any calculation is attempted. Using actual dates would require consideration of the irregular number of days in each month between any two dates. They would never use dates like 25 March and 25 December, either Julian or Gregorian, in such a calculation. After these dates are converted into the Julian date count of days, a simple subtraction gives the elapsed period of time. This period of time can then be converted into Julian centuries by dividing it by 36525. Julian centuries in astronomy are never Julian calendar centuries, they are just a period of 36525 days without any specified beginning or end.

You misunderstand astronomical year numbering and its use in ISO 8601. 44 BC is never called "AD −43", it is simply −43. Although the year number differs, it is only another name for the same year. Indeed, AD, BC and other era designations are not allowed in ISO 8601 dates.

You cannot use a derogatory term like "abnormal" in a Wikipedia article. Your personal opinions are not allowed in Wikipedia. — Joe Kress 03:24, 17 April 2007 (UTC)

Days of the Week

Does one revise the days of the week in the Proleptic Gregorian Calendar? — Preceding unsigned comment added by 204.227.204.234 (talk • contribs)

No, because the Gregorian calendar did not change the days of the week when it dropped ten days in 1582. Thursday 4 October 1582 (Julian) was immediately followed by Friday 15 October 1582 (Gregorian). Thus any Julian calendar date would have the same day of the week after it is converted into the proleptic Gregorian calendar: Thursday 4 October 1582 (Julian) is Thursday 14 October 1582 (Gregorian). It is obvious that the dates have changed from 4 to 14, so if the day of the week is included, the date change can be used to determine whether a specific date was written in the Julian calendar or in the proleptic Gregorian calendar. — Joe Kress 22:10, 18 April 2007 (UTC)

Wouldn't Gregorian leap years in centuries only evenly divisible by 400 mess this up farther in the past? For example 1500 would not be a leap year in the Gregorian calendar but it would be in the Julian. In the Gregorian there would not be a February 29th but there would be in the Julian. What day of the week would February 28th be in the Proleptic gregorian calendar? — Preceding unsigned comment added by 209.193.87.154 (talk • contribs)

February 29, 1500 (Julian) is March 10, 1500 (Gregorian)—both are Saturdays. February 28, 1500 in the proleptic Gregorian calendar is February 19, 1500 in the Julian calendar—both are Wednesdays. All dates have one and only one equivalent in the other calendar and always have the same weekday. Although February 29, 1500 does not exist in the proleptic Gregorian calendar, it can be construed to be the day after February 28, 1500 (Gregorian), that is March 1, 1500 (Gregorian), which is equivalent to February 20, 1500 (Julian). I used Calendrica for these conversions (click on the equivalent date in any other calendar to gain access to drop-down menus of all months and days in that other calendar). — Joe Kress 22:13, 19 April 2007 (UTC)

Since the chart in the article gives the number of days that the proleptic Gregorian calendar varies frim the Julian and this varies over time with the changes not equal to a week this seemed impossible to me so I checked this out using your source, Calendrica. According to this source the days of the week ARE revised as well. For example enter a day in 100 AD and you will see that you are wrong. — Preceding unsigned comment added by 209.193.87.154 (talk • contribs)

Since you did not state what you did, I can only guess. In Calendrica enter any Gregorian date in AD 100, for example, September 1. In the centered box near the top appears "Wednesday, 1 September 100 (Gregorian)". In the left hand box of the next line down appears "Julian: 2 September 100 C.E.". This difference of one day is consistent with an extension of the article's table one century earlier. The first entry is a date in the proleptic Gregorian calendar and the second is the equivalent date in the Julian calendar. Only one day of the week is given because both dates are on a Wednesday. Alternately, you could click on the Julian date, making it the "entered" date. The proleptic Gregorian date still shows Wednesday. The day of the week does not change. — Joe Kress 05:10, 9 May 2007 (UTC)

Ancient dates

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)

Leap years?

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)