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Intercalation (timekeeping)
Intercalation or embolism in timekeeping is the insertion of a leap day, week, or month into some calendar years to make the calendar follow the seasons or moon phases. Lunisolar calendars may require intercalations of days or months. Solar calendars The solar or tropical year does not have a whole number of days (it is about 365.24 days), but a calendar year must have a whole number of days. The most common way to reconcile the two is to vary the number of days in the calendar year. In solar calendars, this is done by adding an extra day ("leap day" or "intercalary day") to a common year of 365 days, about once every four years, creating a leap year that has 366 days ( Julian, Gregorian and Indian national calendars). The Decree of Canopus, issued by the pharaoh Ptolemy III Euergetes of Ancient Egypt in 239 BC, decreed a solar leap day system; an Egyptian leap year was not adopted until 25 BC, when the Roman Emperor Augustus instituted a reformed Alexandrian cal ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Leap Day
A leap year (also known as an intercalary year or bissextile year) is a calendar year that contains an additional day (or, in the case of a lunisolar calendar, a month) compared to a common year. The 366th day (or 13th month) is added to keep the calendar year synchronised with the astronomical year or seasonal year. Since astronomical events and seasons do not repeat in a whole number of days, calendars having a constant number of days each year will unavoidably drift over time with respect to the event that the year is supposed to track, such as seasons. By inserting (" intercalating") an additional day—a leap day—or month—a leap month—into some years, the drift between a civilization's dating system and the physical properties of the Solar System can be corrected. An astronomical year lasts slightly less than 365 days. The historic Julian calendar has three common years of 365 days followed by a leap year of 366 days, by extending February to 29 ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Chinese Calendar
The traditional Chinese calendar, dating back to the Han dynasty, is a lunisolar calendar that blends solar, lunar, and other cycles for social and agricultural purposes. While modern China primarily uses the Gregorian calendar for official purposes, the traditional calendar remains culturally significant. It determines the timing of Chinese New Year with traditions like the twelve animals of the Chinese zodiac, Chinese Zodiac still widely observed. The traditional Chinese calendar uses the Sexagenary cycle, sexagenary cycle, a repeating system of Heavenly Stems and Earthly Branches, to mark years, months, and days. This system, along with astronomical observations and mathematical calculations, was developed to align solar and lunar cycles, though some approximations are necessary due to the natural differences between these cycles. Over centuries, the calendar was refined through advancements in astronomy and horology, with dynasties introducing variations to improve accu ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Hindu Calendar
The Hindu calendar, also called Panchangam, Panchanga (), is one of various lunisolar calendars that are traditionally used in the Indian subcontinent and Southeast Asia, with further regional variations for social and Hindu religious purposes. They adopt a similar underlying concept for timekeeping based on sidereal year for solar cycle, solar cycle and adjustment of lunar cycles in every three years, but differ in their relative emphasis to moon cycle or the sun cycle and the names of months and when they consider the New Year to start. Of the various regional calendars, the most studied and known Hindu calendars are the Shaka era, Shalivahana Shaka (Based on the Shalivahana, King Shalivahana, also the Indian national calendar) found in the Deccan Plateau, Deccan region of Southern India and the Vikram Samvat (Bikrami) found in Nepal and the North and Central regions of India – both of which emphasize the lunar cycle. Their new year starts in spring. In regions such as Tamil ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Computus
As a moveable feast, the date of Easter is determined in each year through a calculation known as – often simply ''Computus'' – or as paschalion particularly in the Eastern Orthodox Church. Easter is celebrated on the first Sunday after the Paschal full moon (a mathematical approximation of the first astronomical full moon, on or after 21 March itself a fixed approximation of the March equinox). Determining this date in advance requires a correlation between the lunar months and the solar year, while also accounting for the month, date, and weekday of the Julian or Gregorian calendar. The complexity of the algorithm arises because of the desire to associate the date of Easter with the date of the Jewish feast of Passover which, Christians believe, is when Jesus was crucified. It was originally feasible for the entire Christian Church to receive the date of Easter each year through an annual announcement by the pope. By the early third century, however, communic ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Hebrew Calendar
The Hebrew calendar (), also called the Jewish calendar, is a lunisolar calendar used today for Jewish religious observance and as an official calendar of Israel. It determines the dates of Jewish holidays and other rituals, such as '' yahrzeits'' and the schedule of public Torah readings. In Israel, it is used for religious purposes, provides a time frame for agriculture, and is an official calendar for civil holidays alongside the Gregorian calendar. Like other lunisolar calendars, the Hebrew calendar consists of months of 29 or 30 days which begin and end at approximately the time of the new moon. As 12 such months comprise a total of just 354 days, an extra lunar month is added every 2 or 3 years so that the long-term average year length closely approximates the actual length of the solar year. Originally, the beginning of each month was determined based on physical observation of a new moon, while the decision of whether to add the leap month was based on observation ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Metonic Cycle
The Metonic cycle or enneadecaeteris (from , from ἐννεακαίδεκα, "nineteen") is a period of almost exactly 19 years after which the lunar phases recur at the same time of the year. The recurrence is not perfect, and by precise observation the Metonic cycle defined as 235 synodic months is just 2 hours, 4 minutes and 58 seconds longer than 19 tropical years. Meton of Athens, in the 5th century BC, judged the cycle to be a whole number of days, 6,940. Using these whole numbers facilitates the construction of a lunisolar calendar. A tropical year (about 365.24 days) is longer than 12 lunar months (about 354.36 days) and shorter than 13 of them (about 383.90 days). In a Metonic calendar (a type of lunisolar calendar), there are twelve years of 12 lunar months and seven years of 13 lunar months. Application in traditional calendars In the Babylonian and Hebrew lunisolar calendars, the years 3, 6, 8, 11, 14, 17, and 19 are the long (13-month) years of the Metonic c ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Lunar Month
In lunar calendars, a lunar month is the time between two successive syzygies of the same type: new moons or full moons. The precise definition varies, especially for the beginning of the month. Variations In Shona, Middle Eastern, and European traditions, the month starts when the young crescent moon first becomes visible, at evening, after conjunction with the Sun one or two days before that evening (e.g., in the Islamic calendar). In ancient Egypt, the lunar month began on the day when the waning moon could no longer be seen just before sunrise. Others run from full moon to full moon. Yet others use calculation, of varying degrees of sophistication, for example, the Hebrew calendar, the Chinese calendar, or the ecclesiastical lunar calendar. Calendars count integer days, so months may be 29 or 30 days in length, in some regular or irregular sequence. Lunar cycles are prominent, and calculated with great precision in the ancient Hindu Panchangam calendar, widely us ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Ayyám-i-Há
Ayyám-i-Há is a period of intercalary days in the Baháʼí calendar, when Baháʼís celebrate the Festival of Ayyám-i-Há. The four or five days of this period are inserted between the last two months of the calendar (Mulk and ʻAláʼ). The length of Ayyám-i-Há varies according to the timing of the following vernal equinox so that the next year always starts on the vernal equinox. 2025 has four days of Ayyám-i-Há: from sunset on Monday, February 24, to sunset on Friday, February 28. History The Báb, the founder of the Bábí Faith, instituted the Badíʻ calendar in the Persian Bayán with 19 months of 19 days each and a period of intercalary days to allow for the calendar to be solar. The introduction of intercalation marked an important break from Islam, as under the Islamic calendar the practice of intercalation had been condemned in the Qurʼan. The Báb did not, however, specify where the intercalary days should go. Baháʼu'lláh, who claimed to be the ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
March Equinox
The March equinox or northward equinox is the equinox on the Earth when the subsolar point appears to leave the Southern Hemisphere and cross the celestial equator, heading northward as seen from Earth. The March equinox is known as the vernal equinox (or spring equinox) in the Northern Hemisphere and as the autumnal equinox (or fall equinox) in the Southern Hemisphere. On the Gregorian calendar at 0° longitude, the northward equinox can occur as early as 19 March (which happened most recently in 1796, and will happen next in 2044), and it can occur as late as 21 March (which happened most recently in 2007, and will happen next in 2102). For a common year the computed time slippage is about 5 hours 49 minutes ''later'' than the previous year, and for a leap year about 18 hours 11 minutes ''earlier'' than the previous year. Balancing the increases of the common years against the losses of the leap years keeps the calendar date of the March equinox from drifting more than ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Hijrah
The Hijrah, () also Hegira (from Medieval Latin), was the journey the prophets and messengers in Islam, Islamic prophet Muhammad and his followers took from Mecca to Medina. The year in which the Hijrah took place is also identified as the epoch of the Islamic calendar, Lunar Hijri and Solar Hijri calendar, Solar Hijri calendars; its date equates to 16 July 622 in the Julian calendar. Early in Muhammad's preaching of Islam, his followers only included his close friends and relatives. Most of his tribesmen, the Quraysh, however, were indifferent to his activities, as they did not appear to be particularly interested in devotional meetings, and accordingly, Muhammad did not encounter any serious opposition from them; that was the case until he began to challenge their beliefs, which caused tensions to arise. In May 622, after having convened twice with members of the Medinan tribes of Banu Aws, Aws and Khazraj at al-'Aqabah near Mina, Saudi Arabia, Mina, Muhammad secretly left ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
