Activation (time calculation)

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The activation or intercalation in the era (from latin intercalatio "intermediary" or "insertion") is the insertion of a certain unit time ( leap , leap month ) for sun or moon calendars or bound moon calendars , to the calendar year, the observable or measurable phases of the heavenly bodies adapt . The years in which such an activation occurs are called leap years (as opposed to: common years ). A special case is the modern leap second , which does not refer to the calendar but the time within a day.

A practically applicable calendar must have an integer number of days (e.g. 365 or 366 days), which a solar year, for example, with its approx. 365 14 days does not have. The aim of the engagement is to achieve an adjustment of the required integer number of the calendar with the non-integer number of days of the solar year.

What is switched on?

When a leap month , a leap day or a leap second is mentioned, this usually means precisely this period of time ( month, day, second ) that is added. If, on the other hand, a leap year is mentioned, this does not mean an additional year , but just a year that differs from a common year in terms of additional (leap) days or (leap) months .

Calendar system (selection) basis What is switched on in the leap year?
Julian calendar solar - Leap day
Gregorian calendar solar - Leap day
Orthodox calendar solar - Leap day
French revolutionary calendar solar - Leap day
Islamic calendar lunar - Leap day
Roman calendar lunisolar Leap month -
Jewish calendar lunisolar Leap month -
Chinese calendar solar + lunisolar Leap month -

More examples

In the Gregorian calendar a leap day is inserted every four years, but not in certain century years that cannot be divided by 400 (such as 1700, 1800, 1900, 2100, ...).

Another example is the Jewish calendar , a lunisolar calendar, also called a bound lunar calendar. It takes into account both the solar year with its 365 14 days, which does not provide a whole number of lunar months with 29 12 days, and the lunar year . Here z. B. in certain years a 13th leap month inserted in order to adapt the calendar to the requirements of a lunar calendar. An ordinary year has 12 months, a leap year has 13 months. The intercalation of dead days is also an option here.

The Roman calendar (initially a lunar calendar, later a lunisolar calendar) worked with switching periods: the dies intercalaris (leap day) and the mensis intercalaris (leap month) within an annus intercalaris (leap year). The year lengths were 355 & 377 and 355 & 378 days.

See also

  • Epagomene - additional days inserted every year