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A calendar is a system of organizing days for social, religious, commercial or administrative purposes. This is done by giving names to periods of time, typically days, weeks, months, and years. A date is the designation of a single, specific day within such a system. A calendar is also a physical record (often paper) of such a system. A calendar can also mean a list of planned events, such as a court calendar or a partly or fully chronological list of documents, such as a calendar of wills. Periods in a calendar (such as years and months) are usually, though not necessarily, synchronized with the cycle of the sun or the moon. The most common type of pre-modern calendar was the lunisolar calendar, lunar calendar that compensates by adding an intercalary months to remain synchronised with the solar year over the long term. The calendar in most widespread use today is the Gregorian calendar, introduced in the 16th century as a modification of the Julian calendar, which was itself a modification of the ancient Roman calendar. The term ''calendar'' itself is taken from ''calendae'', the term for the first day of the month in the Roman calendar, related to the verb ''calare'' "to call out", referring to the "calling" of the new moon when it was first seen.〔''New Shorter Oxford English Dictionary''〕 Latin ''calendarium'' meant "account book, register" (as accounts were settled and debts were collected on the calends of each month). The Latin term was adopted in Old French as ''calendier'' and from there in Middle English as ''calender'' by the 13th century (the spelling ''calendar'' is early modern). ==History== (詳細はtimekeeping, and the year and lunation were most commonly used in pre-modern societies worldwide as time units. Nevertheless, the Roman calendar contained very ancient remnants of a pre-Etruscan 10-month solar year.〔"Religion in the Etruscan period" in (Roman religion ) in Encyclopedia Britannica〕 The first recorded calendars date to the Bronze Age, dependent on the development of writing in the Ancient Near East, the Egyptian and Sumerian calendars. A larger number of calendar systems of the Ancient Near East becomes accessible in the Iron Age, based on the Babylonian calendar. This includes the calendar of the Persian Empire, which in turn gave rise to the Zoroastrian calendar as well as the Hebrew calendar. A great number of Hellenic calendars develop in Classical Greece, and with the Hellenistic period also influence calendars outside of the immediate sphere of Greek influence, giving rise to the various Hindu calendars as well as to the ancient Roman calendar. Calendars in antiquity were lunisolar, depending on the introduction of intercalary months to align the solar and the lunar years. This was mostly based on observation, but there may have been early attempts to model the pattern of intercalation algorithmically, as evidenced in the fragmentary 2nd-century Coligny calendar. The Roman calendar was reformed by Julius Caesar in 45 BC. The Julian calendar was no longer dependent on the observation of the new moon but simply followed an algorithm of introducing a leap day every four years. This created a dissociation of the calendar month from the lunation. The Islamic calendar is based on the prohibition of intercalation (''nasi''') by Muhammad, in Islamic tradition dated to a sermon held on 9 Dhu al-Hijjah AH 10 (Julian date: 6 March 632). This resulted in an observationally based lunar calendar shifting relative to the seasons of the solar year. 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「calendar」の詳細全文を読む スポンサード リンク
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