Where Did Calendars Begin?
Early in history man began counting time by days, months and seasons and so had the beginnings of a calendar. When he studied the supposed movement of the sun more closely he began to use the year as a unit of time. The course of the Sun and the Moon are the most evident forms of 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. 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 large number of calendar systems which were based on the Babylonian calendar, and which were found in the Ancient Near East, date from the Iron Age. Amongst such calendar systems was the calendar system 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 developed in Classical Greece, and with the Hellenistic period also influenced calendars outside of the immediate sphere of Greek influence, giving rise to the various Hindu calendars as well as to the ancient Roman calendar.
The Greeks dated everything from the Olympic Register, a traditional list of the victors in the Olympic Games starting in 776 B.C. The Romans counted time from the founding of their city in 753 B.C. The Mohammedans use the Hejira, or flight of Mohammed from Mecca, A.D. 622. Jewish reckoning dates back to the Creation, calculated as having taken place 3,760 years and three months before Christ’s birth-date.
The Roman calendar was reformed by Julius Caesar in 45 BC., acting on the advice of the astronomer Sosigenes, Julius Caesar fixed the year at 365 ¼ days, giving every fourth year, or leap year, an extra day. But the correction by a whole day every four years was too much, and by the 16th Century the Julian calendar was 13 days behind the solar year.
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.
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 Islamic calendar is based on the prohibition of intercalation (nasi’) by Muhammad, in Islamic tradition dated to a sermon held on (Julian date: 6 March 632). This resulted in an observation-based lunar calendar that shifts relative to the seasons of the solar year.
The Christian practice of dating events from the birth of Christ did not come into general use until the time of Charlemagne (9th Century), and a mistake was made which placed the birth of Christ five years too late.
In 1582, Pope Gregory XIII directed that 10 days should be dropped from the calendar. He also directed that three times in every 400 years the leap year arrangement should be omitted, by not counting as leap years the years ending in two noughts unless they are divisible by 400. This arrangement will keep the calendar and solar year together until the year 5000, when the difference will be one day.
The term calendar 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. 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).
The primary practical use of a calendar is to identify days: to be informed about or to agree on a future event and to record an event that has happened. Days may be significant for agricultural, civil, religious or social reasons. For example, a calendar provides a way to determine when to start planting or harvesting, which days are religious or civil holidays, which days mark the beginning and end of business accounting periods, and which days have legal significance, such as the day taxes are due or a contract expires. Also a calendar may, by identifying a day, provide other useful information about the day such as its season.
Calendars are also used to help people manage their personal schedules, time and activities, particularly when individuals have numerous work, school, and family commitments. People frequently use multiple systems, and may keep both a business and family calendar to help prevent them from overcommitting their time.
Calendars are also used as part of a complete timekeeping system: date and time of day together specify a moment in time. In the modern world, timekeepers can show time, date and weekday.