Calendar Wiki

A lunisolar or solilunar calendar combines the concept of a year (i.e. the revolution time of the planet, usually Earth, around its central star, usually Sun alias Sol) with one or more types of months or lunations (i.e. the revolution time of the planet’s natural satellites, usually Moon alias Luna). For Earth this is a tad over 365 days a year and little less than 30 days per month, so mostly 12 months per year.

If a finer distinction between the two equivalent terms is made for terrestrial calendars, lunisolar calendars will defintely have 365 or 366 days per year with a leap day and solilunar calendars will defintely have 29 or 30 days per month with a leap month.

Terrestrial 7-day week Leap-week calendars can only ever be loosely lunisolar with 52 or 53 weeks per year or loosely solilunar with 4 or 5 weeks per month, most of them have both properties.

Calendars based on seasons (equinox and solstice) and zodiac signs (stellar constellations) are usually solar calendars instead.

Observational 12-lunation calendars without intercalation are lunar calendars instead.

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