History of calendars

Meaning of calender

No.1 a list that shows the days, weeks and months of a particular year.

No.2 a system for dividing time into fixed periods and for marking the beginning and end of a year

Equinox seen from the astronomic calendar of Pizzo Vento at Fondachelli Fantina, Sicily

The course of the sun and the moon are the most salient natural, regularly recurring events useful for timekeeping, thus in pre-modern societies worldwide lunation and the year were most commonly used as time units. Nevertheless, the Roman calendar contained remnants of a very ancient pre-Etruscan 10-month solar year.^[2] The first recorded physical calendars, dependent on the development of writing in the Ancient Near East, are the Bronze Age Egyptian and Sumerian calendars.^[3]

The Vedic India developed a sophisticated time keeping methodology and calendars for Vedic rituals.^[4]

A large number of Ancient Near East calendar systems based on the Babylonian calendar date from the Iron Age, among them the calendar system of the Persian Empire, which in turn gave rise to the Zoroastrian calendar and the Hebrew calendar.^{[citation needed]}

A great number of Hellenic calendars developed in Classical Greece, and in the Hellenistic period gave rise to both the ancient Roman calendar and to various Hindu calendars.^[5] According to Yukio Ohashi, Vedanga field developed from actual astronomical studies in ancient Vedic Period and not derived from other cultures.^[6]

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 46 BC.^[7] 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 observation-based lunar calendar that shifts relative to the seasons of the solar year.

Modern reform

The first calendar reform of the early modern era was the Gregorian calendar, introduced in 1582 based on the observation of a long-term shift between the Julian calendar and the solar year.

Modern calendar

There have been several modern proposals for reform of the calendar, such as the World Calendar, International Fixed Calendar, Holocene calendar, and, recently, the Hanke-Henry Permanent Calendar. Such ideas are mooted from time to time but have failed to gain traction because of the loss of continuity, massive upheaval in implementation, and religious objections.