The Republic of China calendar is the official calendar of the Republic of China. It is used to number the years for official purposes only in the Taiwan area after 1949, it was used in the Chinese mainland from 1912 until the establishment of the People's Republic of China in 1949. Following the Chinese imperial tradition of using the sovereign's era name and year of reign, official ROC documents use the Republic system of numbering years in which the first year was 1912, the year of the establishment of the Republic of China. Months and days are numbered according to the Gregorian calendar; the Gregorian calendar was adopted by the nascent Republic of China effective 1 January 1912 for official business, but the general populace continued to use the traditional Chinese calendar. The status of the Gregorian calendar was unclear between 1916 and 1921 while China was controlled by several competing warlords each supported by foreign colonial powers. From about 1921 until 1928 warlords continued to fight over northern China, but the Kuomintang or Nationalist government controlled southern China and used the Gregorian calendar.
After the Kuomintang reconstituted the Republic of China on 10 October 1928, the Gregorian calendar was adopted, effective 1 January 1929. The People's Republic of China has continued to use the Gregorian calendar since 1949. Despite the adoption of the Gregorian calendar, the numbering of the years was still an issue; the Chinese imperial tradition was to use the emperor's era year of reign. One alternative to this approach was to use the reign of the half-historical, half-legendary Yellow Emperor in the third millennium BC to number the years. In the early 20th century, some Chinese Republicans began to advocate such a system of continuously numbered years, so that year markings would be independent of the Emperor's regnal name; when Sun Yat-sen became the provisional president of the Republic of China, he sent telegrams to leaders of all provinces and announced the 13th day of 11th Month of the 4609th year of the Yellow Emperor's reign to be the first year of the Republic of China. The original intention of the Minguo calendar was to follow the imperial practice of naming the years according to the number of years the Emperor had reigned, a universally recognizable event in China.
Following the establishment of the Republic, hence the lack of an Emperor, it was decided to use the year of the establishment of the current regime. This reduced the issue of frequent change in the calendar, as no Emperor ruled more than 61 years in Chinese history — the longest being the Kangxi Emperor, who ruled from 1662–1722; as Chinese era names are traditionally two characters long, 民國 is employed as an abbreviation of 中華民國. The first year, 1912, is called 民國元年 and 2010, the "99th year of the Republic" is 民國九十九年, 民國99年, or 99. Based on Chinese National Standard CNS 7648: Data Elements and Interchange Formats—Information Interchange—Representation of Dates and Times, year numbering may use the Gregorian system as well as the ROC era. For example, 3 May 2004 may be written 2004-05-03 or ROC 93-05-03; the ROC era numbering happens to be the same as the numbering used by the Juche calendar of North Korea, because its founder, Kim Il-sung, was born in 1912. The years in Japan's Taishō period coincide with those of the ROC era.
In addition to the ROC's Minguo calendar, Taiwanese continue to use the lunar Chinese calendar for certain functions such as the dates of many holidays, the calculation of people's ages, religious functions. The use of the ROC era system extends beyond official documents. Misinterpretation is more in the cases when the prefix is omitted. There have been legislative proposals by pro-Taiwan Independence political parties, such as the Democratic Progressive Party to abolish the Republican calendar in favor of the Gregorian calendar. To convert any Gregorian calendar year between 1912 and the current year to Minguo calendar, 1912 needs to be subtracted from the year in question 1 added. East Asian age reckoning Public holidays in Taiwan
The Islamic, Muslim, or Hijri calendar is a lunar calendar consisting of 12 lunar months in a year of 354 or 355 days. It is used to determine the proper days of Islamic holidays and rituals, such as the annual period of fasting and the proper time for the pilgrimage to Mecca; the civil calendar of all countries where the religion is predominantly Muslim is the Gregorian calendar. Notable exceptions to this rule are Afghanistan, which use the Solar Hijri calendar. Rents and similar regular commitments are paid by the civil calendar; the Islamic calendar employs the Hijri era whose epoch was established as the Islamic New Year of 622 AD/CE. During that year and his followers migrated from Mecca to Yathrib and established the first Muslim community, an event commemorated as the Hijra. In the West, dates in this era are denoted AH in parallel with the Christian and Jewish eras. In Muslim countries, it is sometimes denoted as H from its Arabic form. In English, years prior to the Hijra are reckoned as BH.
The current Islamic year is 1440 AH. In the Gregorian calendar, 1440 AH runs from 11 September 2018 to 30 August 2019. For central Arabia Mecca, there is a lack of epigraphical evidence but details are found in the writings of Muslim authors of the Abbasid era. Inscriptions of the ancient South Arabian calendars reveal the use of a number of local calendars. At least some of these South Arabian calendars followed the lunisolar system. Both al-Biruni and al-Mas'udi suggest that the ancient Arabs used the same month names as the Muslims, though they record other month names used by the pre-Islamic Arabs; the Islamic tradition is unanimous in stating that Arabs of Tihamah and Najd distinguished between two types of months and forbidden months. The forbidden months were four months during which fighting is forbidden, listed as Rajab and the three months around the pilgrimage season, Dhu al-Qa‘dah, Dhu al-Hijjah, Muharram. Information about the forbidden months is found in the writings of Procopius, where he describes an armistice with the Eastern Arabs of the Lakhmid al-Mundhir which happened in the summer of 541 AD/CE.
However, Muslim historians do not link these months to a particular season. The Qur'an links the four forbidden months with Nasī’, a word that means "postponement". According to Muslim tradition, the decision of postponement was administered by the tribe of Kinanah, by a man known as the al-Qalammas of Kinanah and his descendants. Different interpretations of the concept of Nasī’ have been proposed; some scholars, both Muslim and Western, maintain that the pre-Islamic calendar used in central Arabia was a purely lunar calendar similar to the modern Islamic calendar. According to this view, Nasī’ is related to the pre-Islamic practices of the Meccan Arabs, where they would alter the distribution of the forbidden months within a given year without implying a calendar manipulation; this interpretation is supported by Arab historians and lexicographers, like Ibn Hisham, Ibn Manzur, the corpus of Qur'anic exegesis. This is corroborated by an early Sabaic inscription, where a religious ritual was "postponed" due to war.
According to the context of this inscription, the verb ns'’ has nothing to do with intercalation, but only with moving religious events within the calendar itself. The similarity between the religious concept of this ancient inscription and the Qur'an suggests that non-calendaring postponement is the Qur'anic meaning of Nasī’; the Encyclopaedia of Islam concludes "The Arabic system of can only have been intended to move the Hajj and the fairs associated with it in the vicinity of Mecca to a suitable season of the year. It was not intended to establish a fixed calendar to be observed." The term "fixed calendar" is understood to refer to the non-intercalated calendar. Others concur that it was a lunar calendar, but suggest that about 200 years before the Hijra it was transformed into a lunisolar calendar containing an intercalary month added from time to time to keep the pilgrimage within the season of the year when merchandise was most abundant; this interpretation was first proposed by the medieval Muslim astrologer and astronomer Abu Ma'shar al-Balkhi, by al-Biruni, al-Mas'udi, some western scholars.
This interpretation considers Nasī’ to be a synonym to the Arabic word for "intercalation". The Arabs, according to one explanation mentioned by Abu Ma'shar, learned of this type of intercalation from the Jews; the Jewish Nasi was the official. Some sources say that the Arabs followed the Jewish practice and intercalated seven months over nineteen years, or else that they intercalated nine months over 24 years. Postponement of one ritual in a particular circumstance does not imply alteration of the sequence of months, scholars agree that this did not happen. Al-Biruni says this did not happen, the festivals were kept within their season by intercalation every second or third year of a month between Dhu al-Hijjah and Muharram, he says that, in terms of the fixed calendar, not introduced until 10 AH, the first intercalation was, for example, of a month between Dhu al-Hijjah and Muharram, the second of a month between Muharram and Safar, the third of a month between Safar and Rabi'I, so on. The intercalations were arranged.
The notice of interca
The Byzantine calendar called "Creation Era of Constantinople" or "Era of the World", was the calendar used by the Eastern Orthodox Church from c. 691 to 1728 in the Ecumenical Patriarchate. It was the official calendar of the Byzantine Empire from 988 to 1453, of Kievan Rus' and Russia from c. 988 to 1700. Since "Byzantine" is a historiographical term, the original name uses the noun "Roman" as it was how the Eastern Roman Empire continued calling itself; the calendar was based on the Julian calendar, except that the year started on 1 September and the year number used an Anno Mundi epoch derived from the Septuagint version of the Bible. It placed the date of creation at 5509 years before the Incarnation, was characterized by a certain tendency, a tradition among Jews and early Christians to number the years from the calculated foundation of the world, its Year One, marking the supposed date of creation, was September 1, 5509 BC, to August 31, 5508 BC. It is not known when; the first appearance of the term is in the treatise of a certain "monk and priest", who mentions all the main variants of the "World Era" in his work.
Georgios argues that the main advantage of the World era is the common starting point of the astronomical lunar and solar cycles, of the cycle of indictions, the usual dating system in Byzantium since the 6th century. He already regards it as the most convenient for the Easter computus. Complex calculations of the 19-year lunar and 28-year solar cycles within this world era allowed scholars to discover the cosmic significance of certain historical dates, such as the birth or the crucifixion of Jesus; this date underwent minor revisions before being finalized in the mid-7th century, although its precursors were developed c. AD 412. By the second half of the 7th century, the Creation Era was known in Western Europe, at least in Great Britain. By the late 10th century around AD 988, when the era appears in use on official government records, a unified system was recognized across the Eastern Roman world; the era was calculated as starting on September 1, Jesus was thought to have been born in the year 5509 since the creation of the world.
Historical time was thus calculated from the creation, not from Christ's birth, as in the west after the Anno Domini system was adopted between 6th and 9th centuries. The Eastern Church avoided the use of the Anno Domini system of Dionysius Exiguus, since the date of Christ's birth was debated in Constantinople as late as the 14th century. Otherwise the Byzantine calendar was identical to the Julian Calendar except that: the names of the months were transcribed from Latin into Greek; the leap day of the Byzantine calendar was obtained in an identical manner to the bissextile day of the original Roman version of the Julian calendar, by doubling the sixth day before the calends of March, i.e. by doubling 24 February. The Byzantine World Era was replaced in the Orthodox Church by the Christian Era, utilized by Patriarch Theophanes I Karykes in 1597, afterwards by Patriarch Cyril Lucaris in 1626, formally established by the Church in 1728. Meanwhile, as Russia received Orthodox Christianity from Byzantium, she inherited the Orthodox Calendar based on the Byzantine Era.
After the collapse of the Byzantine Empire in 1453, the era continued to be used by Russia, which witnessed millennialist movements in Moscow in AD 1492. It was only in AD 1700 that the Byzantine World Era in Russia was changed to the Julian Calendar by Peter the Great, it still forms the basis of traditional Orthodox calendars up to today. September AD 2000 began the year 7509 AM; the earliest extant Christian writings on the age of the world according to the Biblical chronology are by Theophilus, the sixth bishop of Antioch from the Apostles, in his apologetic work To Autolycus, by Julius Africanus in his Five Books of Chronology. Both of these early Christian writers, following the Septuagint version of the Old Testament, determined the age of the world to have been about 5,530 years at the birth of Christ. Ben Zion Wacholder points out that the writings of the Church Fathers on this subject are of vital significance, in that through the Christian chronographers a window to the earlier Hellenistic biblical chronographers is preserved: An immense intellectual effort was expended during the Hellenistic period by both Jews and pagans to date creation, the flood, building of the Temple...
In the course of their studies, men such as Tatian of Antioch, Clement of Alexandria, Hippolytus of Rome
The traditional China calendar, or Former Calendar, Traditional Calendar or Lunar Calendar, is a lunisolar calendar which reckons years and days according to astronomical phenomena. It is defined by GB/T 33661-2017, "Calculation and promulgation of the Chinese calendar", issued by the Standardisation Administration of China on 12 May 2017. Although modern day China uses the Gregorian calendar, the traditional Chinese calendar governs holidays in China and in overseas Chinese communities, it lists the dates of traditional Chinese holidays and guides people in selecting auspicious days for weddings, moving, or starting a business. Like Chinese characters, variants of this calendar are used in different parts of the Chinese cultural sphere. Korea and the Ryukyu Islands adopted the calendar, it evolved into Korean and Ryukyuan calendars; the main difference from the traditional Chinese calendar is the use of different meridians, which leads to some astronomical events—and calendar events based on them—falling on different dates.
The traditional Japanese calendar derived from the Chinese calendar, but its official use in Japan was abolished in 1873 as part of reforms after the Meiji Restoration. Calendars in Mongolia and Tibet have absorbed elements of the traditional Chinese calendar, but are not direct descendants of it. Days begin and end at midnight, months begin on the day of the new moon. Years begin on the second new moon after the winter solstice. Solar terms govern the end of each month. Written versions in ancient China included stems and branches of the year and the names of each month, including leap months as needed. Characters indicated whether a month was short; the traditional Chinese calendar was developed between 771 and 476 BC, during the Spring and Autumn period of the Eastern Zhou dynasty. Before the Zhou dynasty, solar calendars were used. One version of the solar calendar is the five-elements calendar. A 365-day year was divided into five phases of 73 days, with each phase corresponding to a Day 1 Wu Xing element.
A phase began followed by six 12-day weeks. Each phase consisted of two three-week months. Years began followed by a bǐngzǐ day and a 72-day fire phase. Other days were tracked using the Yellow River Map. Another version is a four-quarters calendar. Weeks were ten days long, with one month consisting of three weeks. A year had 12 months, with a ten-day week intercalated in summer as needed to keep up with the tropical year; the 10 Heavenly Stems and 12 Earthly Branches were used to mark days. A third version is the balanced calendar. A year was 365.25 days, a month was 29.5 days. After every 16th month, a half-month was intercalated. According to oracle bone records, the Shang dynasty calendar was a balanced calendar with 12 to 14 months in a year; the first lunisolar calendar was the Zhou calendar, introduced under the Zhou dynasty. This calendar set the beginning of the year at the day of the new moon before the winter solstice, it set the shàngyuán as the winter solstice of a dīngsì year, making the year it was introduced around 2,758,130.
Several competing lunisolar calendars were introduced by states fighting Zhou control during the Warring States period. The state of Lu issued its own Lu calendar. Jin issued the Xia calendar in AD 102, with a year beginning on the day of the new moon nearest the March equinox. Qin issued the Zhuanxu calendar, with a year beginning on the day of the new moon nearest the winter solstice. Song's Yin calendar began its year on the day of the new moon after the winter solstice; these calendars are known as the six ancient calendars, or quarter-remainder calendars, since all calculate a year as 365 1⁄4 days long. Months begin on the day of the new moon, a year has 12 or 13 months. Intercalary months are added to the end of the year; the Qiang and Dai calendars are modern versions of the Zhuanxu calendar, used by mountain peoples. After Qin Shi Huang unified China under the Qin dynasty in 221 BC, the Qin calendar was introduced, it followed most of the rules governing the Zhuanxu calendar, but the month order was that of the Xia calendar.
The intercalary month, known as the second Jiǔyuè, was placed at the end of the year. The Qin calendar was used into the Han dynasty. Emperor Wu of Han r. 141 – 87 BC introduced reforms halfway through his reign. His Taichu Calendar defined a solar year as 365 385⁄1539 days, the lunar month was 29 43⁄81 days; this calendar introduced the 24 solar terms. Solar terms were paired, with the 12 combined periods known as climate terms; the first solar term of the period was known as a pre-climate, the second was a mid-climate. Months were named for the mid-climat
The 11th century is the period from 1001 to 1100 in accordance with the Julian calendar in the Common Era, the 1st century of the 2nd millennium. In the history of Europe, this period is considered the early part of the High Middle Ages. There was, after a brief ascendancy, a sudden decline of Byzantine power and rise of Norman domination over much of Europe, along with the prominent role in Europe of notably influential popes. In Northern Italy, a growth of population in urban centers gave rise to early organized capitalism and more sophisticated, commercialized culture by the late 11th century. In East Europe, there was the golden age for the principality of Kievan Rus. In Song dynasty China and the classical Islamic world, this century marked the high point for both classical Chinese civilization and technology, classical Islamic science, philosophy and literature. Rival political factions at the Song dynasty court created strife amongst the leading statesmen and ministers of the empire. Chola-era India and Fatimid-era Egypt, had reached their zenith in military might and international influence.
The Western Chalukya Empire rose to power by the end of the century. In this century the Turkish Seljuk dynasty comes to power in Western Asia over the now fragmented Abbasid realm, while the first of the Crusades were waged towards the close of the century. In Japan, the Fujiwara clan continued to dominate the affairs of state. In Korea, the Goryeo Kingdom faced external threats from the Liao dynasty. In Vietnam, the Lý Dynasty began, while in Myanmar the Pagan Kingdom reached its height of political and military power. In the Americas, the Toltec and Mixtec civilizations flourished in Central America, along with the Huari Culture of South America and the Mississippian culture of North America; the Tiwanaku Empire centered around Lake Titicaca collapsed in the first half of the century. In European history, the 11th century is regarded as the beginning of the High Middle Ages, an age subsequent to the Early Middle Ages; the century began while the translatio imperii of 962 was still somewhat novel and ended in the midst of the Investiture Controversy.
It saw the final Christianisation of Scandinavia and the emergence of the Peace and Truce of God movements, the Gregorian Reforms, the Crusades which revitalised a church and a papacy that had survived tarnished by the tumultuous 10th century. In 1054, the Great Schism rent the church in two, however. In Germany, the century was marked by the ascendancy of the Holy Roman Emperors, who hit their high-water mark under the Salians. In Italy, it opened with the integration of the kingdom into the empire and the royal palace at Pavia was summoned in 1024. By the end of the century and Byzantine rule in the Mezzogiorno had been usurped by the Normans and the power of the territorial magnates was being replaced by that of the citizens of the cities in the north. In Britain, it saw the transformation of Scotland into a single, more unified and centralised kingdom and the Norman conquest of England in 1066; the social transformations wrought in these lands brought them into the fuller orbit of European feudal politics.
In France, it saw the nadir of the monarchy and the zenith of the great magnates the dukes of Aquitaine and Normandy, who could thus foster such distinctive contributions of their lands as the pious warrior who conquered Britain and the East and the impious peacelover, the troubadour, who crafted out of the European vernacular its first great literary themes. There were the first figures of the intellectual movement known as Scholasticism, which emphasized dialectic arguments in disputes of Christian theology as well as classical philosophy. In Spain, the century opened with the successes of the last caliphs of Córdoba and ended in the successes of the Almoravids. In between was a period of Christian unification under Navarrese hegemony and success in the Reconquista against the taifa kingdoms that replaced the fallen caliphate. In China, there was a triangular affair of continued war and peace settlements between the Song dynasty, the Tanguts-led Western Xia in the northwest, the Khitans of the Liao dynasty in the northeast.
Meanwhile, opposing political factions evolved at the Song imperial court of Kaifeng. The political reformers at court, called the New Policies Group, were led by Emperor Shenzong of Song and the Chancellors Fan Zhongyan and Wang Anshi, while the political conservatives were led by Chancellor Sima Guang and Empress Dowager Gao, regent of the young Emperor Zhezong of Song. Heated political debate and sectarian intrigue followed, while political enemies were dismissed from the capital to govern frontier regions in the deep south where malaria was known to be fatal to northern Chinese people; this period represents a high point in classical Chinese science and technology, with figures such as Su Song and Shen Kuo, as well as the age where the matured form of the Chinese pagoda was accomplished in Chinese architecture. In India, the Chola Dynasty reached its height of naval power under leaders such as Rajaraja Chola I and Rajendra Chola I, dominating southern India, Sri Lanka, regions of South East Asia.
They sent raids into what is now Thailand. In Japan, the Fujiwara clan dominated central politics by acting as imperial regents, controlling the actions of the Emperor of Japan, who acted as a'puppet monarch' during the Heian period. In the Middle East, the Fatimid Empire of Egypt reached its zenith only to face steep decline, much like the Byzantine Empire in the first half of the century; the Seljuks came to prominence while the Abbasid caliphs held traditional titles without real, tangible authority
Ab urbe condita
Ab urbe condita, or Anno urbis conditæ abbreviated as AUC in either case, is a convention, used in antiquity and by classical historians to refer to a given year in Ancient Rome. Ab urbe condita means "from the founding of the City," while anno urbis conditæ means "in the year since the City's founding." Therefore, the traditional year of the foundation of Rome, 753 BC, would be written AUC 1, while AD 1 would be AUC 754. The foundation of the Empire in 27 BC would be AUC 727. Usage of the term was more common during the Renaissance, when editors sometimes added AUC to Roman manuscripts they published, giving the false impression that the convention was used in antiquity. In reality, the dominant method of identifying years in Roman times was to name the two consuls who held office that year. In late antiquity, regnal years were in use, as was the Diocletian era in Roman Egypt after AD 293, in the Byzantine Empire after AD 537, following a decree by Justinian; the traditional date for the founding of Rome, 21 April 753 BC, is due to Marcus Terentius Varro.
Varro may have used the consular list and called the year of the first consuls "ab urbe condita 245," accepting the 244-year interval from Dionysius of Halicarnassus for the kings after the foundation of Rome. The correctness of this calculation has not been confirmed. From the time of Claudius onward, this calculation superseded other contemporary calculations. Celebrating the anniversary of the city became part of imperial propaganda. Claudius was the first to hold magnificent celebrations in honor of the anniversary of the city, in AD 48, the eight hundredth year from the founding of the city. Hadrian and Antoninus Pius held similar celebrations, in AD 121, in AD 147 and AD 148, respectively. In AD 248, Philip the Arab celebrated Rome's first millennium, together with Ludi saeculares for Rome's alleged tenth sæculum. Coins from his reign commemorate the celebrations. A coin by a contender for the imperial throne, explicitly states "ear one thousand and first", an indication that the citizens of the empire had a sense of the beginning of a new era, a Sæculum Novum.
The Anno Domini year numbering was developed by a monk named Dionysius Exiguus in Rome in AD 525, as a result of his work on calculating the date of Easter. Dionysius did not use the AUC convention, but instead based his calculations on the Diocletian era; this convention had been in use since AD 293, the year of the tetrarchy, as it became impractical to use regnal years of the current emperor. In his Easter table, the year AD 532 was equated with the 248th regnal year of Diocletian; the table counted the years starting from the presumed birth of Christ, rather than the accession of the emperor Diocletian on 20 November AD 284, or as stated by Dionysius: "sed magis elegimus ab incarnatione Domini nostri Jesu Christi annorum tempora praenotare". Blackburn and Holford-Strevens review interpretations of Dionysius which place the Incarnation in 2 BC, 1 BC, or AD 1, it has been calculated that the year AD 1 corresponds to AUC 754, based on the epoch of Varro. Thus, AUC 1 = 753 BC AUC 753 = 1 BC AUC 754 = AD 1 AUC 1000 = AD 247 AUC 1229 = AD 476 AUC 2206 = AD 1453 AUC 2753 = AD 2000 AUC 2772 = AD 2019 List of Latin phrases
The Nanakshahi calendar is a tropical solar calendar, used in Sikhism and is based on the'Barah Maha'. Barah Maha was composed by the Sikh Gurus and translates as the "Twelve Months", it is a poem reflecting the changes in nature which are conveyed in the twelve-month cycle of the Year. The year begins with 1 Chet corresponding to 14 March; the first year of the Nanakshahi Calendar starts in 1469 CE: the year of the birth of Guru Nanak Dev. The Nanakshahi Calendar is named after the founder of Guru Nanak Dev. Sikhs have traditionally recognised luni-solar calendars: the Nanakshahi and Khalsa. Traditionally, both these calendars followed the Bikrami calendar with the Nanakshahi year beginning on Katak Pooranmashi and the Khalsa year commencing with Vaisakhi; the methods for calculating the beginning of the Khalsa era were based on the Bikrami calendar. The year length was the same as the Bikrami solar year. According to Steel, the calendar has twelve lunar months that are determined by the lunar phase, but thirteen months in leap years which occur every 2–3 years in the Bikrami calendar to sync the lunar calendar with its solar counterpart.
Kay abbreviates the Khalsa Era as KE. References to the Nanakshahi Era have been made in historic documents. Banda Singh Bahadur adopted the Nanakshahi calendar in 1710 C. E. after his victory in Sirhind according to which the year 1710 C. E. became Nanakshahi 241. However, Singh states the date of the victory as 14 May 1710 CE. According to Dilagira, Banda "continued adopting the months and the days of the months according to the Bikrami calendar". Banda Singh Bahadur minted new coins called Nanakshahi. Herrli states. Although Banda may have proclaimed this era, it cannot be traced in contemporary documents and does not seem to have been used for dating". According to The Panjab Past and Present, it is Gian Singh who "is the first to use Nanak Shahi Samvats along with those of Bikrami Samvats" in the Twarikh Guru Khalsa. According to Singha, Gian Singh was a Punjabi author born in 1822. Gian Singh wrote the Twarikh Guru Khalsa in 1891; the revised Nanakshahi calendar was designed by Pal Singh Purewal to replace the Bikrami calendar.
The epoch of this calendar is the birth of the first Sikh Guru, Nanak Dev in 1469 and the Nanakshahi year commences on 1 Chet. New Year's Day falls annually on; the start of each month is fixed. According to Kapel, the solar accuracy of the Nanakshahi calendar is linked to the Gregorian civil calendar; this is because the Nanaskhahi calendar uses the tropical year instead of using the sidereal year, used in the Bikrami calendar or the old Nanakshahi and Khalsa calendars. The amended Nanakshahi calendar was adopted in 1998 but implemented in 2003 by the Shiromani Gurdwara Prabhandak Committee to determine the dates for important Sikh events; the calendar was implemented during the SGPC presidency of Sikh scholar Prof. Kirpal Singh Badungar at Takhat Sri Damdama Sahib in the presence of Sikh leadership. Nanakshahi Calendar recognizes the adoption event, of 1999 CE, in the Sikh history when SGPC released the first calendar with permanently fixed dates in the Tropical Calendar. Therefore, the calculations of this calendar do not regress back from 1999 CE into the Bikrami era, fixes for all time in the future.
Features of the Original Nanakshahi calendar: Uses the accurate Tropical year rather than the Sidereal year Called Nanakshahi after Guru Nanak Year 1 is the Year of Guru Nanak's Birth. As an example, April 14, 2019 CE is Nanakshahi 551. Is Based on Gurbani – Month Names are taken from Guru Granth Sahib Contains 5 Months of 31 days followed by 7 Months of 30 days Leap year every 4 Years in which the last month has an extra day Approved by Akal Takht in 2003 In 2010, the Shiromani Gurdwara Prabhandak Committee modified the calendar so that the dates for the start of the months are movable so that they coincide with the Bikrami calendar and changed the dates for various Sikh festivals so they are based upon the lunar phase; this has created controversy with some bodies adopting the original 2003 version called the "Mool Nanakshahi Calendar" and others, the 2010 version. By 2014, the SGPC had scrapped the original Nanakshahi calendar from 2003 and reverted to the Bikrami calendar however it was still published under the name of Nanakshahi.
The Sikh bodies termed it a step taken under pressure from the Shiromani Akali Dal. There is some controversy about the acceptance of the calendar altogether among certain sectors of the Sikh world. SGPC president, Gobind Singh Longowal, on 13 March 2018 urged all Sikhs to follow the current Nanakshahi calendar; the previous SGPC President before Longowal, Prof. Kirpal Singh Badungar, tried to appeal the Akal Takht to celebrate the birthday of Guru Gobind Singh on 23 Poh as per the original Nanakshahi calendar, but the appeal was denied; the PSGPC and a majority of the other gurdwara managements across the world are opposing the modified version of the calendar citing that the SGPC reverted to the Bikrami calendar. They argue that in the Bikrami calendar, dates of many gurpurbs coincide, thereby creating confusion among the Sikh Panth. According to Ahaluwalia, the Nanakshahi calendar goes against the use of lunar Bikrami dates by the Gurus themselves and is contradictory, it begins with the year of birth of