Dual dating
Encyclopedia
In historical materials, dates will often be indicated with what appears to be duplicate, or excessive digits, sometimes separated by a hyphen or a slash. This is often referred to as double dating. The need for double dating arose from the transition from an older calendar to a newer one. For example, in "10/21 February 1750/51", the dual day of the month is due to the leap year
correction of the Julian calendar
by the Gregorian calendar
, and the dual year is due to some countries beginning their numbered year on 1 January while others were still using another date.
There is some confusion as to which calendar alteration OS or NS refers to: the change of the start of the year, or the transition of one style of calendar to another. Historically, OS referred only to the start of the year change to 1 January from March 25, and some historians still believe this is the best practice. However, OS and NS may refer to both alterations of the calendar.
During the period between 1582, when the first countries adopted the Gregorian calendar
, and 1923, when the last Europe
an country adopted it, it was often necessary to indicate the date of an event in both the Julian calendar
and the Gregorian calendar. Also, even before 1582, the year sometimes had to be double dated because different countries began the year on different dates.
For instance, the calendar in the British Empire
did not immediately change. Woolley, writing in his biography of John Dee
(1527–1608/9), notes that immediately after 1582 English
letter writers "customarily" used "two dates" on their letters, one OS and one NS. The Calendar Act 1750
altered the start of the year, and also aligned the British calendar 11 days later to comply with the Gregorian calendar.
, Korea
, and China
started using the Gregorian calendar on 1 January 1873, 1896, and 1912, respectively. They had used lunisolar calendar
s previously. None of them used the Julian calendar; the Old Style and New Style dates in these countries usually mean the older lunisolar dates and the newer Gregorian calendar dates respectively. In these countries, the old style calendars were similar, but not all the same. The Arabic numerals
may be used for both calendar dates in modern Japanese and Korean languages, but not Chinese.
6'. The preceding day, 31 December 1872, was .
Japan currently employs two calendar systems: Gregorian and the Japanese era name
calendar. Specifically, the months and days now correspond to those of the Gregorian calendar, but the year is expressed as an offset of the era
. For example, the Gregorian year 2007 corresponds to Heisei
19. An era does not necessarily begin on January 1.
that still used the lunisolar calendar. The lunisolar Korean calendar
is now used in very limited unofficial purposes only.
started using the Gregorian calendar on 1 January 1912, but the lunisolar Chinese calendar
is still used along with the Gregorian calendar, especially when determining certain traditional holidays. The reference has been a longitude of 120°E since 1929, which is also used for Chinese Standard Time (UTC+8
). China, Hong Kong
, Macau
, Malaysia, Indonesia
, Singapore
and Taiwan
all have legal holidays based on the lunisolar Chinese calendar, with the most important one being the Chinese New Year
.
To visually distinguish old and new style dates, GB
/T 15835-1995, General rules for writing numerals in publications, which is a national standard of the People's Republic of China, requires writing new style dates with Arabic numerals but old style dates with Chinese character
s, never Arabic numerals.
In Taiwan, even though new style dates are written in Chinese characters in very formal texts, it is now common to see Arabic numerals in new style dates in less formal texts. When writing old style dates, Chinese characters are usually used while Arabic numerals are considered very casual and strongly discouraged as in Mainland China. The calendar year in Taiwan
is usually expressed as the "Year of the Republic" — counting Year 1 as the foundation of the Republic of China in 1912 CE.
When 'translating' dates from historical documents to current documents for dates that have been incorrectly double dated by historians, both years should be entered into contemporary documents until a copy of the original primary source can be checked, verifying which style was used in the 'official record'. Often errors have been perpetuated from the early 19th century and still exist today. When 'translating' dates from historical documents to current documents for dates that have been correctly double dated by historians, the standard practice is to enter the earlier year first, and the later year second.
In either case, to avoid further confusion, contemporary researchers should be vigilant about annotating both dates with a notation indicating the type of date, and using a slash rather than a hyphen to indicate alternate dates. When notating the type of date, contemporary researchers wishing to indicate the leap year correction would do well to use a J for Julian, and a G, for Gregorian, and OS/NS for the start of the year alteration. For instance 12 Feb 1750 OS,J in the British Empire would be 23 Feb 1751 NS,G. This might also be accurately written 12/23 Feb 1750/1 OS,J/NS,G.
Leap year
A leap year is a year containing one extra day in order to keep the calendar year synchronized with the astronomical or seasonal year...
correction of the Julian calendar
Julian calendar
The Julian calendar began in 45 BC as a reform of the Roman calendar by Julius Caesar. It was chosen after consultation with the astronomer Sosigenes of Alexandria and was probably designed to approximate the tropical year .The Julian calendar has a regular year of 365 days divided into 12 months...
by the Gregorian calendar
Gregorian calendar
The Gregorian calendar, also known as the Western calendar, or Christian calendar, is the internationally accepted civil calendar. It was introduced by Pope Gregory XIII, after whom the calendar was named, by a decree signed on 24 February 1582, a papal bull known by its opening words Inter...
, and the dual year is due to some countries beginning their numbered year on 1 January while others were still using another date.
Europe and its colonies: Old Style and New Style dates
"Old Style" (OS) and "New Style" (NS) are sometimes added to dates to identify which date corresponds to an OS calendar that was used prior to a NS calendar. In some cases, such as some places in East Asia, both styles are currently in use. In other places such as Europe, the NS supplanted the OS, but the transition from the OS to the NS varied greatly by geography and the date of transition. Consequently, in places that have fully transitioned from an OS calendar to a NS calendar, dual dates appear in documents over an extended period of time, even centuries.There is some confusion as to which calendar alteration OS or NS refers to: the change of the start of the year, or the transition of one style of calendar to another. Historically, OS referred only to the start of the year change to 1 January from March 25, and some historians still believe this is the best practice. However, OS and NS may refer to both alterations of the calendar.
During the period between 1582, when the first countries adopted the Gregorian calendar
Gregorian calendar
The Gregorian calendar, also known as the Western calendar, or Christian calendar, is the internationally accepted civil calendar. It was introduced by Pope Gregory XIII, after whom the calendar was named, by a decree signed on 24 February 1582, a papal bull known by its opening words Inter...
, and 1923, when the last Europe
Europe
Europe is, by convention, one of the world's seven continents. Comprising the westernmost peninsula of Eurasia, Europe is generally 'divided' from Asia to its east by the watershed divides of the Ural and Caucasus Mountains, the Ural River, the Caspian and Black Seas, and the waterways connecting...
an country adopted it, it was often necessary to indicate the date of an event in both the Julian calendar
Julian calendar
The Julian calendar began in 45 BC as a reform of the Roman calendar by Julius Caesar. It was chosen after consultation with the astronomer Sosigenes of Alexandria and was probably designed to approximate the tropical year .The Julian calendar has a regular year of 365 days divided into 12 months...
and the Gregorian calendar. Also, even before 1582, the year sometimes had to be double dated because different countries began the year on different dates.
For instance, the calendar in the British Empire
British Empire
The British Empire comprised the dominions, colonies, protectorates, mandates and other territories ruled or administered by the United Kingdom. It originated with the overseas colonies and trading posts established by England in the late 16th and early 17th centuries. At its height, it was the...
did not immediately change. Woolley, writing in his biography of John Dee
John Dee (mathematician)
John Dee was an English mathematician, astronomer, astrologer, occultist, navigator, imperialist and consultant to Queen Elizabeth I. He devoted much of his life to the study of alchemy, divination and Hermetic philosophy....
(1527–1608/9), notes that immediately after 1582 English
England
England is a country that is part of the United Kingdom. It shares land borders with Scotland to the north and Wales to the west; the Irish Sea is to the north west, the Celtic Sea to the south west, with the North Sea to the east and the English Channel to the south separating it from continental...
letter writers "customarily" used "two dates" on their letters, one OS and one NS. The Calendar Act 1750
Calendar (New Style) Act 1750
The Calendar Act 1750 is an Act of the Parliament of Great Britain...
altered the start of the year, and also aligned the British calendar 11 days later to comply with the Gregorian calendar.
East Asia
JapanMeiji period
The , also known as the Meiji era, is a Japanese era which extended from September 1868 through July 1912. This period represents the first half of the Empire of Japan.- Meiji Restoration and the emperor :...
, Korea
Korean Empire
The Greater Korean Empire was an empire of Korea that succeeded the Joseon Dynasty.In October 1897, Emperor Gojong proclaimed the new entity at Gyeongungung Palace and oversaw the partially successful modernization of the military, economy, land system, education system, and various industries...
, and China
China
Chinese civilization may refer to:* China for more general discussion of the country.* Chinese culture* Greater China, the transnational community of ethnic Chinese.* History of China* Sinosphere, the area historically affected by Chinese culture...
started using the Gregorian calendar on 1 January 1873, 1896, and 1912, respectively. They had used lunisolar calendar
Lunisolar calendar
A lunisolar calendar is a calendar in many cultures whose date indicates both the moon phase and the time of the solar year. If the solar year is defined as a tropical year then a lunisolar calendar will give an indication of the season; if it is taken as a sidereal year then the calendar will...
s previously. None of them used the Julian calendar; the Old Style and New Style dates in these countries usually mean the older lunisolar dates and the newer Gregorian calendar dates respectively. In these countries, the old style calendars were similar, but not all the same. The Arabic numerals
Arabic numerals
Arabic numerals or Hindu numerals or Hindu-Arabic numerals or Indo-Arabic numerals are the ten digits . They are descended from the Hindu-Arabic numeral system developed by Indian mathematicians, in which a sequence of digits such as "975" is read as a numeral...
may be used for both calendar dates in modern Japanese and Korean languages, but not Chinese.
Japan
Japan started using the Gregorian calendar on 1 January 1873, locally known as 'the first day of the first month of MeijiMeiji period
The , also known as the Meiji era, is a Japanese era which extended from September 1868 through July 1912. This period represents the first half of the Empire of Japan.- Meiji Restoration and the emperor :...
6'. The preceding day, 31 December 1872, was .
Japan currently employs two calendar systems: Gregorian and the Japanese era name
Japanese era name
The Japanese era calendar scheme is a common calendar scheme used in Japan, which identifies a year by the combination of the and the year number within the era...
calendar. Specifically, the months and days now correspond to those of the Gregorian calendar, but the year is expressed as an offset of the era
Japanese era name
The Japanese era calendar scheme is a common calendar scheme used in Japan, which identifies a year by the combination of the and the year number within the era...
. For example, the Gregorian year 2007 corresponds to Heisei
Heisei
is the current era name in Japan. The Heisei era started on 8 January 1989, the first day after the death of the reigning Emperor, Hirohito. His son, Akihito, succeeded to the throne...
19. An era does not necessarily begin on January 1.
Korea
Korea started using the Gregorian calendar on 1 January 1896, which was the 17th day of the 11th lunar month in not only Korea, but also in ChinaQing Dynasty
The Qing Dynasty was the last dynasty of China, ruling from 1644 to 1912 with a brief, abortive restoration in 1917. It was preceded by the Ming Dynasty and followed by the Republic of China....
that still used the lunisolar calendar. The lunisolar Korean calendar
Korean calendar
The traditional Korean calendar is a lunisolar calendar, like the traditional calendars of other East Asian countries. Dates are calculated from Korea's meridian, and observances and festivals are based in Korean culture....
is now used in very limited unofficial purposes only.
China
The Republic of ChinaRepublic of China
The Republic of China , commonly known as Taiwan , is a unitary sovereign state located in East Asia. Originally based in mainland China, the Republic of China currently governs the island of Taiwan , which forms over 99% of its current territory, as well as Penghu, Kinmen, Matsu and other minor...
started using the Gregorian calendar on 1 January 1912, but the lunisolar Chinese calendar
Chinese calendar
The Chinese calendar is a lunisolar calendar, incorporating elements of a lunar calendar with those of a solar calendar. It is not exclusive to China, but followed by many other Asian cultures as well...
is still used along with the Gregorian calendar, especially when determining certain traditional holidays. The reference has been a longitude of 120°E since 1929, which is also used for Chinese Standard Time (UTC+8
UTC+8
UTC+08:00 is an identifier for a time offset from UTC of +08:00. In ISO 8601 the associated time would be written as .With an estimated population of 1.53 billion living within the time zone, roughly 22.5% of the world population, it is the most populous time zone in world, as well as a possible...
). China, Hong Kong
Hong Kong
Hong Kong is one of two Special Administrative Regions of the People's Republic of China , the other being Macau. A city-state situated on China's south coast and enclosed by the Pearl River Delta and South China Sea, it is renowned for its expansive skyline and deep natural harbour...
, Macau
Macau
Macau , also spelled Macao , is, along with Hong Kong, one of the two special administrative regions of the People's Republic of China...
, Malaysia, Indonesia
Indonesia
Indonesia , officially the Republic of Indonesia , is a country in Southeast Asia and Oceania. Indonesia is an archipelago comprising approximately 13,000 islands. It has 33 provinces with over 238 million people, and is the world's fourth most populous country. Indonesia is a republic, with an...
, Singapore
Singapore
Singapore , officially the Republic of Singapore, is a Southeast Asian city-state off the southern tip of the Malay Peninsula, north of the equator. An island country made up of 63 islands, it is separated from Malaysia by the Straits of Johor to its north and from Indonesia's Riau Islands by the...
and Taiwan
Taiwan
Taiwan , also known, especially in the past, as Formosa , is the largest island of the same-named island group of East Asia in the western Pacific Ocean and located off the southeastern coast of mainland China. The island forms over 99% of the current territory of the Republic of China following...
all have legal holidays based on the lunisolar Chinese calendar, with the most important one being the Chinese New Year
Chinese New Year
Chinese New Year – often called Chinese Lunar New Year although it actually is lunisolar – is the most important of the traditional Chinese holidays. It is an all East and South-East-Asia celebration...
.
To visually distinguish old and new style dates, GB
Guobiao
Guóbiāo is usually the phonetic transcription of the word "National Standards" in Chinese.It could mean any of the standards issued by the Standardization Administration of China , the Chinese National Committee of the ISO and IEC....
/T 15835-1995, General rules for writing numerals in publications, which is a national standard of the People's Republic of China, requires writing new style dates with Arabic numerals but old style dates with Chinese character
Chinese character
Chinese characters are logograms used in the writing of Chinese and Japanese , less frequently Korean , formerly Vietnamese , or other languages...
s, never Arabic numerals.
In Taiwan, even though new style dates are written in Chinese characters in very formal texts, it is now common to see Arabic numerals in new style dates in less formal texts. When writing old style dates, Chinese characters are usually used while Arabic numerals are considered very casual and strongly discouraged as in Mainland China. The calendar year in Taiwan
Minguo calendar
The Republic of China calendar is the method of numbering years currently used in the Republic of China . It was used in mainland China from 1912 until the founding of the People's Republic of China in 1949....
is usually expressed as the "Year of the Republic" — counting Year 1 as the foundation of the Republic of China in 1912 CE.
Use of dates from historical documents in contemporary documents
There was a great deal of confusion when calendars changed, and the confusion continues today. For instance, although the transition in the West often 'moved' the start of the year from March to January, and every person automatically became 10 to 13 days older by fiat when the Gregorian calendar replaced the Julian, the change of the calendar by official decree actually often took place on an historical date which was not in January, February, or March. As explained above, in the British Empire, including the American colonies, the OS change to NS was in September of 1752. Thus, in addition to the 11 day discrepancy, the actual date of the OS/NS change in September 1752 created confusion in months other than January through March. For example, in the American colonies dual dating of the year other than in the months of January, February and March is extant in records in quite a few months. Further complicating accurate attempts at determining a date, in some cases historians did not differentiate between the years.When 'translating' dates from historical documents to current documents for dates that have been incorrectly double dated by historians, both years should be entered into contemporary documents until a copy of the original primary source can be checked, verifying which style was used in the 'official record'. Often errors have been perpetuated from the early 19th century and still exist today. When 'translating' dates from historical documents to current documents for dates that have been correctly double dated by historians, the standard practice is to enter the earlier year first, and the later year second.
In either case, to avoid further confusion, contemporary researchers should be vigilant about annotating both dates with a notation indicating the type of date, and using a slash rather than a hyphen to indicate alternate dates. When notating the type of date, contemporary researchers wishing to indicate the leap year correction would do well to use a J for Julian, and a G, for Gregorian, and OS/NS for the start of the year alteration. For instance 12 Feb 1750 OS,J in the British Empire would be 23 Feb 1751 NS,G. This might also be accurately written 12/23 Feb 1750/1 OS,J/NS,G.
See also
- World CalendarWorld calendarThe World Calendar is a proposed reform of the Gregorian calendar created by Elisabeth Achelis of Brooklyn, New York in 1930.-Features:The World Calendar is a 12-month, perennial calendar with equal quarters. It is perennial, or perpetual, because it remains the same every year.Each quarter begins...
- Calculation of Julian day
- Calendar reformCalendar reformA calendar reform is any significant revision of a calendar system. The term sometimes is used instead for a proposal to switch to a different calendar.Most calendars have several rules which could be altered by reform:...
- ComputusComputusComputus is the calculation of the date of Easter in the Christian calendar. The name has been used for this procedure since the early Middle Ages, as it was one of the most important computations of the age....
for a more complete description of the lunar aspects of the Gregorian calendar - Greek Old CalendaristsGreek Old CalendaristsGreek Old Calendarists are groups that separated from the Orthodox Church of Greece or from the Patriarchate of Constantinople, precipitated by disagreement over the abandonment of the traditional Julian Calendar.- History :Up until the early 20th century, the Eastern Orthodox Church used the...
- List of calendars
- International Fixed CalendarInternational Fixed CalendarThe International Fixed calendar is a solar calendar proposal for calendar reform designed by Moses B...
: another calendar reform proposed before the World Calendar