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The Solar Hijri calendar ((ペルシア語:گاهشماری هجری خورشیدی), (パシュトー語:لمريز لېږدیز کلیز)), also called the Solar Hejri calendar〔 or Shamsi Hijri calendar, and abbreviated as SH, is the official calendar of Iran and Afghanistan. It begins on the vernal equinox as determined by astronomical calculation 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 for predicting the date of the vernal equinox, because it uses astronomical observations rather than mathematical rules.〔M. Heydari-Malayeri, (A concise review of the Iranian calendar ), Paris Observatory.〕 Each of the twelve months corresponds with a zodiac sign. The first six months have 31 days, the next five have 30 days, and the last month has 29 days in usual years but 30 days in leap years. The New Year's Day always falls on the March equinox. == In Iran == On 21 February 1911, the second Persian parliament adopted as the official calendar of Iran the Jalālī sidereal calendar with months bearing the names of the twelve constellations of the zodiac and the years named for the animals of the duodecennial cycle; it remained in use until 1925. The present Iranian calendar was legally adopted on 31 March 1925, under the early Pahlavi dynasty. The law said that the first day of the year should be the first day of spring in "the true solar year", "as it has been" ever so. It also fixed the number of days in each month, which previously varied by year with the sidereal zodiac. It revived the ancient Persian names, which are still used. It specified the origin of the calendar (Hegira of Muhammad from Mecca to Medina in 622 CE). It also deprecated the 12-year cycles of the Chinese-Uighur calendar which were not officially sanctioned but were commonly used. The first six months (Farvardin–Shahrivar) have 31 days, the next five (Mehr–Bahman) have 30 days, and the last month (Esfand) has 29 days or 30 days in leap years. This is a simplification of the Jalali calendar, in which the commencement of the month is tied to the sun's passage from one zodiacal sign to the next. The sun is travelling fastest through the signs in early January (Dey) and slowest in early July (Tir). The current time between the vernal equinox and the autumnal equinox is about 186 days and 10 hours, the opposite duration about 178 days, 20 hours). The Solar Hijri calendar ((ペルシア語:گاهشماری هجری خورشیدی)) produces a five-year leap year interval after about every seven four-year leap year intervals. It usually follows a 33-year cycle with occasional interruptions by single 29-year or 37-year subcycles. The reason for this behaviour is (as explained above) that it tracks the observed vernal equinox. By contrast, some less accurate predictive algorithms are suggestion based on confusion between average tropical year (365.2422 days, approximated with near 128-year cycles or 2820-year great cycles) and the mean interval between spring equinoxes (365.2424 days, approximated with a near 33-year cycle). In 1976, Shah Mohammad Reza Pahlavi changed the origin of the calendar, using the beginning the reign of Cyrus the Great as the first day, rather than the Hejra of Muhammad. Overnight, the year changed from 1355 to 2535. The change lasted till the Islamic Revolution in Iran, 1979; at which time the calendar was reverted to Solar Hijri. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Solar Hijri calendar」の詳細全文を読む スポンサード リンク
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