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
Twenty-seventh Dynasty of Egypt
The Twenty-seventh Dynasty of Egypt known as the First Egyptian Satrapy was a province of the Achaemenid Persian Empire between 525 BC and 404 BC. It was founded by Cambyses II, the King of Persia, after his conquest of Egypt and subsequent crowning as Pharaoh of Egypt, was disestablished upon the rebellion and crowning of Amyrtaeus as Pharaoh. A second period of Achaemenid rule in Egypt occurred under the Thirty-first Dynasty of Egypt; the last pharaoh of the 26th Dynasty, Psamtik III, was defeated by Cambyses II at the battle of Pelusium in the eastern Nile delta in May of 525 BC. Cambyses was crowned Pharaoh of Egypt in the summer of that year at the latest, beginning the first period of Persian rule over Egypt. Egypt was joined with Cyprus and Phoenicia to form the sixth satrapy of the Achaemenid Empire, with Aryandes as the local satrap; as Pharaoh of Egypt, Cambyses' reign saw the fiscal resources of traditional Egyptian temples diminished considerably. One decree, written on papyrus in demotic script ordered a limitation on resources to all Egyptian temples, excluding Memphis and Wenkhem.
Cambyses left Egypt sometime in early 522 BC, dying en route to Persia, was nominally succeeded by his younger brother Bardiya, although contemporary historians suggest Bardiya was Gaumata, an impostor, that the real Bardiya had been murdered some years before by Cambyses, ostensibly out of jealousy. Darius I, suspecting this impersonation, led a coup against "Bardiya" in September of that year, overthrowing him and being crowned as King and Pharaoh the next morning; as the new Persian King, Darius spent much of his time quelling rebellions throughout his empire. Sometime in late 522 BC or early 521 BC a local Egyptian prince led a rebellion and declared himself Pharaoh Petubastis III; the main cause of this rebellion is uncertain, but the Ancient Greek military historian Polyaenus states that it was oppressive taxation imposed by the satrap Aryandes. Polyaenus further writes that Darius himself marched to Egypt, arriving during a period of mourning for the death of the sacred Herald of Ptah bull.
Darius made a proclamation that he would award a sum of one hundred talents to the man who could produce the next Herald, impressing the Egyptians with his piety such that they flocked en masse to his side, ending the rebellion. Darius took a greater interest in Egyptian internal affairs than Cambyses, he codified the laws of Egypt, notably completed the excavation of a canal system at Suez, allowing passage from the Bitter Lakes to the Red Sea, much preferable to the arduous desert land route. This feat allowed Darius to import skilled Egyptian laborers and artisans to construct his palaces in Persia; the result of this was a minor brain drain in Egypt, due to the loss of these skilled individuals, creating a demonstrable lowering of quality in Egyptian architecture and art from this period. Darius was more devoted to supporting Egyptian temples than Cambyses, earning himself a reputation for religious tolerance in the region. In 497 BC, during a visit by Darius to Egypt, Aryandes was executed for treason, most for attempting to issue his own coinage, a visible attempt to distance Egypt from the rest of the Persian Empire.
Darius died in 486 BC, was succeeded by Xerxes I. Upon the accession of Xerxes, Egypt again rebelled, this time under Psamtik IV, although different sources dispute that detail. Xerxes quelled the rebellion, installing his brother Achaemenes as satrap. Xerxes ended the privileged status of Egypt held under Darius, increased supply requirements from the country to fund his invasion of Greece. Furthermore, Xerxes promoted the Zoroastrian god Ahura Mazda at the expense of traditional Egyptian deities, permanently stopped the funding of Egyptian monuments. Xerxes was murdered in 465 BC by Artabanus, beginning a dynastic struggle that ended with Artaxerxes I being crowned the next King and Pharaoh. In 460 BC another major Egyptian rebellion took place, led by a Libyan chief named Inaros II assisted by the Athenians of Greece. Inaros defeated an army led by Achaemenes, killing the satrap in the process, took Memphis exerting control over large parts of Egypt. Inaros and his Athenian allies were defeated by a Persian army led by general Megabyzus in 454 BC and sent into retreat.
Megabyzus promised Inaros no harm would come of him or his followers if he surrendered and submitted to Persian authority, terms Inaros agreed to. Artaxerxes had Inaros executed, although how and when is a matter of dispute. Artaxerxes died in 424 BC. Artaxerxes successor, Xerxes II only ruled for forty-five days, being murdered by his brother Sogdianus. Sogdianus was murdered by his brother Ochus, who became Darius II. Darius II ruled from 423 BC to 404 BC, nearing the end of his reign a rebellion led by Amyrtaeus took place beginning as early as 411 BC. In 405 BC Amyrtaeus, with the help of Cretan mercenaries expelled the Persians from Memphis, declaring himself Pharaoh the next year and ending the 27th Dynasty. Darius II's successor, Artaxerxes II made attempts to begin an expedition to retake Egypt, but due to political difficulty with his brother Cyrus the Younger, abandoned the effort. Artaxerxes II was still recognized as the rightful Pharaoh in some parts of Egypt as late as 401 BC, although his sluggish response to the situation allowed Egypt to solidify its independence.
During the period of independent rule three indigenous dynasties reigned: the 28th, 29th, 30th Dynasty. Artaxe
Balinese saka calendar
The Balinese saka calendar is one of two calendars used on the Indonesian island of Bali. Unlike the 210-day pawukon calendar, it is based on the phases of the Moon, is the same length as the Gregorian year. Based on a lunar calendar, the saka year comprises sasih, of 30 days each. However, because the lunar cycle is shorter than 30 days, the lunar year has a length of 354 or 355 days, the calendar is adjusted to prevent it losing synchronization with the lunar or solar cycles; the months are adjusted by allocating two lunar days to one solar day every 9 weeks. This day is called ngunalatri, Sanskrit for "minus one night". To stop the Saka from lagging behind the Gregorian calendar – as happens with the Islamic calendar, an extra month, known as an intercalary month, is added after the 11th month, or after the 12th month; the length of these months is calculated according to the normal 63-day cycle. An intercalary month is added whenever necessary to prevent the final day of the 7th month, known as Tilem Kapitu, from falling in the Gregorian month of December.
The names the twelve months are taken from a mixture of Old Balinese and Sanskrit words for 1 to 12, are as follows: Kasa Karo Katiga Kapat Kalima Kanem Kapitu Kawalu Kasanga Kadasa Jyestha SadhaEach month begins the day after a new moon and has 15 days of waxing moon until the full moon 15 days of waning, ending on the new moon. Both sets of days are numbered 1 to 15; the first day of the year is the day after the first new moon in March. Note, that Nyepi falls on the first day of Kadasa, that the years of the Saka era are counted from that date; the calendar is 78 years behind the Gregorian calendar, is calculated from the beginning of the Saka Era in India. It is used alongside the 210-day Balinese pawukon calendar, Balinese festivals can be calculated according to either year; the Indian saka calendar was used for royal decrees as early as the ninth century CE. The same calendar was used in Java until Sultan Agung replaced it with the Javanese calendar in 1633; the Balinese Hindu festival of Nyepi, the day of silence, marks the start of the Saka year.
Tilem Kepitu, the last day of the 7th month, is known as Siva Ratri, is a night dedicated to the god Shiva. Devotees stay up all meditate. There are another 24 ceremonial days in the Saka year celebrated at Purnama. Eiseman, Fred B. Jr, Bali: Sekalia and Niskala Volume I: Essays on Religion and Art pp 182–185, Periplus Editions, 1989 ISBN 0-945971-03-6 Haer, Debbie Guthrie. ISBN 981 3018 496 Hobart, Angela. ISBN 0 631 17687 X Ricklefs, M. C.
6th century BC
The 6th century BC started the first day of 600 BC and ended the last day of 501 BC. This century represents the peak of a period in human history popularly known as Axial Age; this period saw the emergence of five major thought streams springing from five great thinkers in different parts of the world: Buddha and Mahavira in India, Zoroaster in Persia, Pythagoras in Greece and Confucius in China. Pāṇini, in India, composed a grammar for Sanskrit, in this century or later; this is the oldest still known grammar of any language. In Western Asia, the first half of this century was dominated by the Neo-Babylonian or Chaldean empire, which had risen to power late in the previous century after rebelling against Assyrian rule; the Kingdom of Judah came to an end in 586 BC when Babylonian forces under Nebuchadnezzar II captured Jerusalem, removed most of its population to their own lands. Babylonian rule was ended in the 540s by Cyrus; the Persian Empire continued to expand and grew into the greatest empire the world had known at the time.
In Iron Age Europe, the Celtic expansion was in progress. China was in the Autumn period. Mediterranean: Beginning of Greek philosophy, flourishes during the 5th century BC The late Hallstatt culture period in Eastern and Central Europe, the late Bronze Age in Northern Europe East Asia: the Spring and Autumn period. Confucianism and Moism flourish. Laozi founds Taoism West Asia: During the Persian empire, Zoroaster, a.k.a. Zarathustra, founded Zoroastrianism, a dualistic philosophy; this was the time of the Babylonian captivity of the ancient Jews. Ancient India: the Buddha and Mahavira found Buddhism and Jainism The decline of the Olmec civilization in Central America Mid-6th century BC: Foundation of Temple of Olympian Zeus. 598 BC: Jehoiachin succeeds Jehoiakim as King of Judah. 16 March 597 BC: Babylonians capture Jerusalem, replace Jehoiachin with Zedekiah as king. 595 BC: Psammetichus II succeeds Necho II as King of Egypt. 594 BC: Solon appointed Archon of Athens. 590 BC: Egyptian army sacks Napata, compelling the Cushite court to move to a more secure location at Meroe near the sixth Cataract.
589 BC: Apries succeeds Psammetichus II as King of Egypt. 588 BC: Nebuchadrezzar II of Babylon begins siege of Jerusalem. The conquerors destroy exile the land's remaining inhabitants. Babylonian Captivity for the Jews begins. 586 BC: death of King Ding of Zhou, King of the Zhou Dynasty of China 28 May 585 BC: A solar eclipse occurs as predicted by Thales, while Alyattes is battling Cyaxares. This leads to a truce; this is one of the cardinal dates. 585 BC/584 BC: Astyages succeeds Cyaxares as King of the Medes. 585 BC: King Jian of Zhou becomes King of the Zhou Dynasty. 583 BC: The Babylonians begin a siege against Tyre. 582 BC: Pythian Games founded at Delphi. 580 BC: Cambyses I succeeds Cyrus I as King of Anshan and head of the Achaemenid dynasty. 580 BC: Isthmian Games founded at Corinth 579 BC: Servius Tullius succeeds the assassinated Lucius Tarquinius Priscus as King of Rome. 573 BC: Nemean Games founded at Nemea. 572 BC: Death of King Jian of Zhou, King of the Zhou Dynasty of China. 571 BC: King Ling of Zhou becomes King of the Zhou Dynasty of China.
570 BC: Amasis II succeeds Apries as King of Egypt. 570 BC: Pythagoras of Samos is born. 570 BC: End of the Babylonian siege against the city of Tyre with a partial victory by the Babylonians. It was the longest siege of the city in history, lasting 13 years. 568 BC: Amtalqa succeeds his brother Aspelta as King of Kush. 562 BC: Amel-Marduk succeeds Nebuchadnezzar as King of Babylon. 560 BC: Neriglissar succeeds Amel-Marduk as King of Babylon. 560 BC/561 BC: Croesus becomes King of Lydia. 560 BC: Pisistratus seizes the Acropolis of Athens and declares himself tyrant. He is deposed in the same year. 550s BC: Carthage conquers Sicily and Corsica. 559 BC: King Cambyses I of Anshan dies and is succeeded by his son Cyrus II the Great. 558 BC: Hegesias removed as Archon of Athens. 558 BC: The Chinese state of Jin defeats its rival Qin in battle. 556 BC: Pisistratus is exiled from Athens to Euboea. 556 BC: Labashi-Marduk succeeds Neriglissar as King of Babylon. 556 BC/555 BC: Nabonidus succeeds Labashi-Marduk as King of Babylon.
550 BC: Abdera is destroyed by the Thracians. 550 BC: Cyrus II the Great overthrows Astyages of the Medes, establishing the Persian Empire. 550 BC: The Late Mumun Period begins in the Korean peninsula. 547 BC: Croesus, Lydian King, is defeated by Cyrus of Persia near the River Halys. 546 BC: Cyrus of Persia completes his conquest of Lydia, makes Pasargadae his capital. 544 BC: People of Teos migrate to Abdera, Thrace to escape the yoke of Persia. 544 BC: King Jing of Zhou becomes King of the Zhou Dynasty of China. 543 BC: Prince Vijaya establishes a Sinhalese dynasty of Sri Lanka. 543 BC: Pisistratus, tyrant of Athens, purifies the island of Delos. 540 BC: Greek city of Elea of southern Italy founded. 540 BC: Persians conquer Lycian city of Xanthos, now in southern Turkey. 539 BC: Babylon is conquered by Cyrus the Great, defeating Nabonidus. 538 BC: Return of some Jews from Babylonian exile who build the Second Temple about fifty years after the destruction of the First Temple, from 520 BC–516 BC. 537 BC: Jews transported to Babylon are allowed to return to Jerusalem, bringing to a close the Babylonian captivity.
536 BC: According to tradition, the Biblical prophet Daniel receives an angelic visitor
The Dragon is the fifth of the 12-year cycle of animals which appear in the Chinese zodiac related to the Chinese calendar. The Year of the Dragon is associated with pronounced chen, it has been proposed by one academic researcher that the Earthly Branch character may have been associated with scorpions. In the Buddhist calendar used in Thailand, Laos and Sri Lanka, the Dragon is replaced by the nāga. In the Gurung zodiac, the Dragon is replaced by the eagle. People born within these date ranges can be said to have been born in the "Year of the Dragon", while bearing the following elemental sign: There are marked spikes in the birth rates of countries that use the Chinese zodiac or places with substantial Overseas Chinese populations during the year of the Dragon, because such "Dragon babies" are considered to be lucky and have desirable characteristics that lead to better life outcomes; the recent phenomenon of planning a child’s birth in the Dragon year has led to hospital overcapacity issues and an uptick in infant mortality rates toward the end of these years due to strained neonatal resources.
Among the 12 animal signs, the Monkey has the most tacit understanding with the Dragon people. The cunning Rat can be a good partner with the Dragon to make something big; the Dragon people can live with the Snake, for the Snake can prevent the Dragon from behaving outrageously. People under the signs of the Rooster, Rabbit, Goat and Horse like to be friends with the Dragon, as they admire the Dragon's beautiful bearing and strength. Two Dragons can get along well with each other. However, the relationship between the Dragon and the Ox people is tense, because both of them are majestic; the people whom the Dragon feels headaches with the most are the Dog people. They feel uncomfortable due to the Dog's close guard
Indian national calendar
The Indian national calendar, sometimes called the Shalivahana Shaka calendar. It is used, alongside the Gregorian calendar, by The Gazette of India, in news broadcasts by All India Radio and in calendars and communications issued by the Government of India; the Saka calendar is used in Java and Bali among Indonesian Hindus. Nyepi, the "Day of Silence", is a celebration of the Saka new year in Bali. Nepal's Nepal Sambat evolved from the Saka calendar. Prior to colonization, the Philippines used to apply the Saka calendar as well as suggested by the Laguna Copperplate Inscription; the term may ambiguously refer to the Hindu calendar. The historic Shalivahana era calendar is still used, it has years. The calendar months follow the signs of the tropical zodiac rather than the sidereal zodiac used with the Hindu calendar. Chaitra has 30 days and starts on March 22, except in leap years, when it has 31 days and starts on March 21; the months in the first half of the year all have 31 days, to take into account the slower movement of the sun across the ecliptic at this time.
The names of the months are derived from older, Hindu lunisolar calendars, so variations in spelling exist, there is a possible source of confusion as to what calendar a date belongs to. Years are counted in the Saka era. To determine leap years, add 78 to the Saka year – if the result is a leap year in the Gregorian calendar the Saka year is a leap year as well, its structure is just like the Persian calendar. Senior Indian Astrophysicist Meghnad Saha was the head of the Calendar Reform Committee under the aegis of the Council of Scientific and Industrial Research. Other members of the Committee were: A. C. Banerjee, K. K. Daftari, J. S. Karandikar, Gorakh Prasad, R. V. Vaidya and N. C. Lahiri, it was Saha's effort. The task before the Committee was to prepare an accurate calendar based on scientific study, which could be adopted uniformly throughout India, it was a mammoth task. The Committee had to undertake a detailed study of different calendars prevalent in different parts of the country. There were thirty different calendars.
The task was further complicated by the fact that religion and local sentiments were integral to those calendars. India's first prime minister, Jawaharlal Nehru, in his preface to the Report of the Committee, published in 1955, wrote: “They represent past political divisions in the country.... Now that we have attained Independence, it is desirable that there should be a certain uniformity in the calendar for our civic and other purposes, this should be done on a scientific approach to this problem.” Usage started at 1 Chaitra 1879, Saka Era, or 22 March 1957. Report of the Calendar Reform Committee – online link. Mapping Time: The Calendar and its History by E. G. Richards, 1998, pp. 184–185. Calendars and their History Indian Calendars Positional astronomy in India Indian National Calendar abstract