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Muslim calendar (also called Hijrī calendar or Islamic calendar. Dating system used in the Muslim world (except Turkey, which adopted the Gregorian calendar in 1925) and based on a year of 12 months, each month beginning approximately at the time of the New Moon. (The Iranian calendar, however, is based on a solar year.) The months are alternately 30 and 29 days long except for the 12th, Dhū al-Ḥijjah, the length of which is varied in a 30-year cycle intended to keep the calendar in step with the true phases of the Moon. In 11 years of this cycle, Dhū al-Ḥijjah has 30 days, and in the other 19 years it has 29. Thus the year has either 354 or 355 days. No months are intercalated, so that the named months do not remain in the same seasons but retrogress through the entire solar, or seasonal, year (of about 365.25 days) every 32.5 solar years. Britannica Alexander Demidov); Iranian calendar (The Iranian calendars (Persian: Gahshomariye Irani) are a succession of calendars invented or used for over two millennia in Iran (Persia). One of the longest chronological records in human history, the Iranian calendar has been modified time and again during its history to suit administrative, climatic, and religious purposes. The modern Iranian calendar is now the official calendar in Iran and Afghanistan. It begins on the vernal equinox as determined by astronomical calculations for the Iran Standard Time meridian (52.5°E or GMT+3.5h). This determination of starting moment is more accurate than the Gregorian calendar as far as predicting the date of the vernal equinox is concerned. Its years are designated AP, short for Anno Persico. The Iranian year usually begins within a day of 21 March of the Gregorian calendar. WK Alexander Demidov); Persian calendar (The Iranian calendar also known as Persian calendar or the Jalāli Calendar is a solar calendar currently used in Iran and Afghanistan. It is observation-based, rather than rule-based, beginning each year on the vernal equinox as precisely determined by astronomical observations from Tehran (or the 52.5°E meridian) and Kabul. This makes it more accurate than Gregorian calendar, but harder to work out which years are leap years.  wikia.com Alexander Demidov) |
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восточный календарь any dating system based on a year consisting of synodic months–i.e., complete cycles of phases of the Moon. In every solar year (or year of the seasons), there are about 12.37 synodic months. Therefore, if a lunar-year calendar is to be kept in step with the seasonal year, a periodic intercalation (addition) of days is necessary. The Sumerians were probably the first to develop a calendar based entirely on the recurrence of lunar phases. Each Sumero-Babylonian month began on the first day of visibility of the new Moon. Although an intercalary month was used periodically, intercalations (intercalation) were haphazard, inserted when the royal astrologers realized that the calendar had fallen severely out of step with the seasons. Starting about 380 BC, however, fixed rules regarding intercalations were established, providing for the distribution of seven intercalary months at designated intervals over 19-year periods. Greek astronomers also devised rules for intercalations to coordinate the lunar and solar years. It is likely that the Roman republican calendar was based on the lunar calendar of the Greeks. Lunar calendars remain in use among certain religious groups today. The Jewish calendar (Jewish religious year), which supposedly dates from 3,760 years and three months before the Christian Era (BCE) is one example. The Jewish religious year begins in autumn and consists of 12 months alternating between 30 and 29 days. It allows for a periodic leap year and an intercalary month. Another lunar calendar, the Muslim (Muslim calendar), dates from the Hegira–July 15, AD 622, the day on which the prophet Muammad began his migration from Mecca to Medina. It makes no effort to keep calendric and seasonal years together. Britannica | |
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lunar calendar (Alexander Demidov) |
