Intercalation (timekeeping)

The involvement or intercalation into the era (from Latin intercalatio " interposition " or " insertion ") is the insertion of a given unit of time ( second, minute, hour, day, week, month, year) in a given calendar - time accounting system such as solar calendar or to adjust the lunar calendar it observable or measurable phases of the stars.

Already the Roman calendar - originally a 10 -month Lunar calendar - worked with switching periods that were called this intercalaris ( leap day ), mens intercalaris ( intercalary month ) and annus intercalaris ( leap year).

A practically applicable for handling calendar must have an integer number of days, the eg a solar year with its 365 ¼ days does not have. Adjusting the required integrality of the calendar (for example, 365 days) and the accuracy of the solar year with its non-integer number of days a leap day is inserted in the Gregorian calendar every four years, in particular the century years that are not divisible by 400 are like 1700, 1800 1900, 2100, are not.

Another example is the Jewish calendar with its Lunisolarjahr - a solar year with lunar months. It takes into account both the solar year with its 365 ¼ days, that not a whole number of lunar months ( 29 ½ days ) supplies, as well as the lunar year. Here is pushed, for example, in some years a 13th month to adapt to the requirements of a lunar calendar the calendar. An ordinary year so has 12 months, a leap year has 13 months. The intercalation of dead days here is a possibility.