旧式与新式日期

舊日期（O.S.）和新日期（N.S.）分別表示日曆更改之前和之後的日曆系統。通常，它們指的是從儒略曆到公曆的變化，如1582年至1923年間的歐洲的各個國家。

在英格蘭、威爾斯、愛爾蘭和英國的美洲殖民地，有兩次日曆變化，都是在1752年。第一次是將新年的開始從3月25日（淑女節（英语：Lady Day），天使報喜節）調整為 1 月 1 日；這是蘇格蘭在1600年就做的更改。第二次是放棄儒略曆，轉而採用公曆，跳過9月份的11天^[2]^[3]。為了適應這兩種的日曆變化，作者使用雙重日期（英语：dual dating），通過根據兩種日期風格給出日期來識別給定的日期。

對於俄羅斯等未進行年初調整的國家^[a]，O.S.和N.S.分別簡單地表示儒略曆和公曆的系統。

儒略曆和公曆日期之間的差異

更正日曆的需要源於認識到一年中天數的正確數字不是儒略曆假設的365.25（365天6小時），而是略少（約365.242天）。因為儒略曆有太多的閏年，結果是，在4世紀決定的復活節日期計算基礎，已經偏離了現實。公曆改革還處理了這些在325年至1582年之間的累積差異，跳過10天將教會春分日（英语：Ecclesiastical full moon）設置為3月21日：325年第一次尼西亞大公會議制定的中位數日期。

1699年之後採用公曆的國家需要為儒略曆從那時起添加的每個後續新世紀多跳過一天。當大英帝國在1752年這樣做時，差距已經擴大到11天^[b]。當俄羅斯在1918年這樣做時（作為其民曆（英语：Civil calendar）），需要跳過13天^[c]。

英國及其殖民地或屬地

在大不列顛王國及其屬地中，1750年曆法 (新式)（英语：Calendar (New Style) Act 1750）對曆法同時進行了兩項更改。第一項適用於英格蘭、威爾斯、愛爾蘭和英國殖民地，將年初從3月25日改為1月1日，從「1751年12月 31日之後的第二天」開始生效。^[6]^[d]（蘇格蘭在1600年1月1日已經做出了這方面的更改。）^[7]^[8]。第二項（實際上^[e]）是採用公曆取代儒略曆。因此，「新式」可以指年初調整為採用公曆，或兩者的組合。正是通過在1750年曆法中的使用，區分「舊式」和「新式」符號才開始普遍使用。

年初的調整

註解

^ By decrees (1735, 1736) of Peter the Great in December 1699 (with effect from 1 January 1700), Russia changed its start of year from September to January and adopted the AD era in place of Anno Mundi.^[4]^[5]
^ Because 1600 was a leap year in both calendars, only one extra Julian leap day (in 1700) needed to be taken into account.
^ Because 1600 was a leap year in both calendars, three extra Julian leap days (in 1700, 1800 and 1900) needed to be taken into account.
^ The act has to use this formulation since "1 January 1752" was still ambiguous.
^ The Calendar Act does not mention Pope Gregory

參考文獻

^ The London Gazette | From Tuesday September 1 O.S. to Saturday September 16 N.S. 1752. London Gazette. 1 September 1752, (9198): 1.
^ Poole 1995，第95–139頁.
^ Spathaky, Mike. Old Style and New Style Dates and the change to the Gregorian Calendar. [19 August 2023]. . "Before 1752, parish registers, in addition to a new year heading after 24th March showing, for example '1733', had another heading at the end of the following December indicating '1733/4'. This showed where the Historical Year 1734 started even though the Civil Year 1733 continued until 24th March. ... We as historians have no excuse for creating ambiguity and must keep to the notation described above in one of its forms. It is no good writing simply 20th January 1745, for a reader is left wondering whether we have used the Civil or the Historical Year. The date should either be written 20th January 1745 OS (if indeed it was Old Style) or as 20th January 1745/6. The hyphen (1745-6) is best avoided as it can be interpreted as indicating a period of time."
^ Полное собрание законов Российской империи. Том III [Complete Collection of Laws of the Russian Empire. Volume III.]. 10 December 1699: 682. 已忽略未知参数|entry-url= (帮助); |entry=被忽略 (帮助)
^ Полное собрание законов Российской империи. Том III [Complete Collection of Laws of the Russian Empire. Volume III.]. 20 December 1699: 683. 已忽略未知参数|entry-url= (帮助); |entry=被忽略 (帮助)
^ Bond 1875，page 91.
^ Steele 2000，第4頁.
^ Bond 1875，xvii–xviii: original text of the Scottish decree.

來源

Bond, John James. Handy Book of Rules and Tables for Verifying Dates With the Christian Era Giving an Account of the Chief Eras and Systems Used by Various Nations...'. London: George Bell & Sons. 1875 [13 March 2016]. （原始内容存档于21 November 2020）.
Cheney, C. R.; Jones, Michael (编). A Handbook of Dates for Students of British History (PDF). Royal Historical Society Guides and Handbooks 4 Revised. Cambridge: Cambridge University Press. 2000: 17–20. ISBN 978-0-521-77095-8.
Gerard, John. General Chronology#Beginning of the year. 天主教百科全书 3. New York: Robert Appleton Company. 1908.
Russia: the October (November) Revolution Online. Encyclopædia Britannica. 2007 [18 March 2007].
Steele, Duncan. Marking Time: the epic quest to invent the perfect calendar. New York: John Wiley & Sons. 2000. ISBN 978-0471404217.
Poole, Robert. 'Give us our eleven days!': calendar reform in eighteenth-century England. Past & Present (Oxford Academic). 1995, (149): 95–139. doi:10.1093/past/149.1.95. （原始内容存档于5 December 2014）.

外部連結

Untangling Lady Day dating and the Julian Calendar by Erin Blake (Folger Library)
The Perpetual Calendar by Toke Nørby - Details of conversion for many countries
Side-by-side Old style–New style reference by Petko Yotov
Calendar Converter by John Walker

[6] By decrees (1735, 1736) of Peter the Great in December 1699 (with effect from 1 January 1700), Russia changed its start of year from September to January and adopted the AD era in place of Anno Mundi.^[4]^[5]

[7] Because 1600 was a leap year in both calendars, only one extra Julian leap day (in 1700) needed to be taken into account.

[8] Because 1600 was a leap year in both calendars, three extra Julian leap days (in 1700, 1800 and 1900) needed to be taken into account.

[10] The act has to use this formulation since "1 January 1752" was still ambiguous.

[13] The Calendar Act does not mention Pope Gregory

[1] The London Gazette | From Tuesday September 1 O.S. to Saturday September 16 N.S. 1752. London Gazette. 1 September 1752, (9198): 1.

[FOOTNOTEPoole199595–139-2] Poole 1995，第95–139頁.

[MS2-3] Spathaky, Mike. Old Style and New Style Dates and the change to the Gregorian Calendar. [19 August 2023]. . "Before 1752, parish registers, in addition to a new year heading after 24th March showing, for example '1733', had another heading at the end of the following December indicating '1733/4'. This showed where the Historical Year 1734 started even though the Civil Year 1733 continued until 24th March. ... We as historians have no excuse for creating ambiguity and must keep to the notation described above in one of its forms. It is no good writing simply 20th January 1745, for a reader is left wondering whether we have used the Civil or the Historical Year. The date should either be written 20th January 1745 OS (if indeed it was Old Style) or as 20th January 1745/6. The hyphen (1745-6) is best avoided as it can be interpreted as indicating a period of time."

[4] Полное собрание законов Российской империи. Том III [Complete Collection of Laws of the Russian Empire. Volume III.]. 10 December 1699: 682. 已忽略未知参数|entry-url= (帮助); |entry=被忽略 (帮助)

[Ukase_1736-5] Полное собрание законов Российской империи. Том III [Complete Collection of Laws of the Russian Empire. Volume III.]. 20 December 1699: 683. 已忽略未知参数|entry-url= (帮助); |entry=被忽略 (帮助)

[FOOTNOTEBond1875[httpsarchiveorgdetailshandybookofrules00bondpage91mode1up_page_91]-9] Bond 1875，page 91.

[FOOTNOTESteele20004-11] Steele 2000，第4頁.

[FOOTNOTEBond1875[httpsarchiveorgdetailshandybookofrules00bondpagen20mode1up_xvii]–xviii:_original_text_of_the_Scottish_decree-12] Bond 1875，xvii–xviii: original text of the Scottish decree.

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