Most lunar calendars, except the Hijri, are in fact lunisolar calendars. That is, months are kept on a lunar cycle, but then intercalary months are added to bring the lunar cycles into synchronisation with the solar year.
Because there are about twelve lunations (synodic months) in a solar year, this period (354.37 days) is sometimes referred to as a lunar year.
All these calendars have a variable number of months in a year. The reason for this is that a year is not evenly divisible by an exact number of lunations, so without the addition of intercalary months the seasons would drift each year. This results in a thirteen-month year every two or three years.
Some lunar calendars are calibrated by annual natural events which are affected by lunar cycles as well as the solar cycle. An example of this is the lunar calendar of the Banks Islands which includes three months in which the edible palolo worm mass on the beaches. These events occurs at the last quarter of the lunar month, as the reproductive cycle of the palolos is synchronised with the moon.
The average length of the synodic month is 29.530589 days. This requires the length of a month to be alternately 29 and 30 days (termed respectively hollow and full). The distribution of hollow and full months can be determined using continued fractions, and examining successive approximations for the length of the month in terms of fractions of a day. In the list below, after the number of days listed in the numerator, an integer number of months as listed in the denominator have been completed:
:29 / 1 (error: 1 day after about 2 months) :30 / 1 (error: 1 day after about 2 months) :59 / 2 (error: 1 day after about 33 months) :443 / 15 (error: 1 day after about 30 years) :502 / 17 (error: 1 day after about 70 years) :1447 / 49 (error: 1 day after about 3 millennia) :25101 / 850 (error: dependent on change of synodic month value) :765433 / 25920 (error: 1 day after about 16 millennia) (Hebrew Calendar)
These fractions can be used in the construction of lunar calendars, or in combination with a solar calendar to produce a lunisolar calendar. The 49-month cycle was proposed as the basis of an alternative Easter computation by Isaac Newton around 1700. The tabular Islamic calendar's 360-month cycle is equivalent to 24×15 months minus a correction of one day.
Category:Calendars Category:Specific calendars
ar:تقويم قمري bs:Lunarni kalendar br:Deiziadur loarel ca:Calendari lunar cs:Lunární kalendář de:Lunarkalender el:Σεληνιακό ημερολόγιο es:Calendario lunar eo:Luna kalendaro fr:Calendrier lunaire ko:태음력 id:Kalender candra ia:Calendario lunar it:Anno lunare he:לוח שנה ירחי jv:Pananggalan candra sw:Kalenda ya mwezi ku:Salnameya heyvê mk:Лунарен календар ms:Takwim qamari nl:Maankalender ja:太陰暦 nn:Måneår km:ចន្ទគតិ pl:Kalendarz księżycowy pt:Calendário lunar ru:Лунный календарь sk:Lunárny kalendár sr:Лунарни календар sh:Lunarni kalendar fi:Kuukalenteri sv:Månkalender ta:சந்திர நாட்காட்டி te:చాంద్రమాన కేలండర్ th:ปฏิทินจันทรคติ uk:Місячний календар vi:Âm lịch zh:阴历This text is licensed under the Creative Commons CC-BY-SA License. This text was originally published on Wikipedia and was developed by the Wikipedia community.
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