System of Calendars | eDominations

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Published in Germany - Political debates and analysis - 4 - 26 Mar 21 22:43

Systems^{of Calendars}

A full calendar system has a different calendar date for every day. Thus the week cycle is by itself not a full calendar system; neither is a system to name the days within a year without a system for identifying the years.
The simplest calendar system just counts time periods from a reference date. This applies for theÂ Julian dayÂ orÂ Unix Time. Virtually the only possible variation is using a different reference date, in particular, one less distant in the past to make the numbers smaller. Computations in these systems are just a matter of addition and subtraction.
Other calendars have one (or multiple) larger units of time.Â
Calendars that contain one level of cycles:

week and weekdayÂ â€“ this system (without year, the week number keeps on increasing) is not very common

year and ordinal date within the year, e.g., theÂ ISO 8601 ordinal date system

Calendars with two levels of cycles:

year, month, and dayÂ â€“ most systems, including theÂ Gregorian calendarÂ (and its very similar predecessor, theÂ Julian calendar), theÂ Islamic calendar, theÂ Solar Hijri calendarÂ and theÂ Hebrew calendar

year, week, and weekdayÂ â€“ e.g., theÂ ISO week date

Cycles can be synchronized with periodic phenomena:

Very commonly a calendar includes more than one type of cycle or has both cyclic and non-cyclic elements.Lunar calendarsÂ are synchronized to the motion of the Moon (lunar phases); an example is the Islamic calendar.

Solar calendarsÂ are based on perceivedÂ seasonalÂ changes synchronized to the apparent motion of the Sun; an example is theÂ Persian calendar.

Lunisolar calendarsÂ are based on a combination of both solar and lunar reckonings; examples include theÂ traditional calendar of China, theÂ Hindu calendarÂ in India and Nepal, and the Hebrew calendar.

The week cycle is an example of one that is not synchronized to any external phenomenon (although it may have been derived from lunar phases, beginning anew every month).

Most calendars incorporate more complex cycles. For example, the vast majority of them track years, months, weeks and days. The seven-day week is practically universal, though its use varies. It has run uninterrupted for millennia

1. Solar

Solar calendars assign aÂ dateÂ to eachÂ solar day. A day may consist of the period betweenÂ sunriseÂ andÂ sunset, with a following period ofÂ night, or it may be a period between successive events such as two sunsets. The length of the interval between two such successive events may be allowed to vary slightly during the year, or it may be averaged into aÂ mean solar day. Other types of calendar may also use a solar day.

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2. Lunar

Not all calendars use the solar year as a unit. A lunar calendar is one in which days are numbered within eachÂ lunar phaseÂ cycle. Because the length of theÂ lunar monthÂ is not an even fraction of the length of theÂ tropical year, a purely lunar calendar quickly drifts against the seasons, which do not vary much near the equator. It does, however, stay constant with respect to other phenomena, notablyÂ tides. An example is theÂ Islamic calendar. Alexander Marshack, in a controversial reading,Â believed that marks on a bone baton (c. 25,000 BC) represented a lunar calendar. Other marked bones may also represent lunar calendars. Similarly, Michael Rappenglueck believes that marks on a 15,000-year-old cave painting represent a lunar calendar.

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3. Lunisolar
AÂ lunisolar calendarÂ is a lunar calendar that compensates by adding an extra month as needed to realign the months with the seasons. Prominent examples of lunisolar calendar areÂ Hindu calendarÂ andÂ Buddhist calendarÂ that are popular inÂ South AsiaÂ andÂ Southeast Asia. Another example is the Hebrew calendar which uses aÂ 19-year cycle.

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