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A lunar calendar is a calendar that is based on cycles of the lunar phases. Because there are slightly more than twelve lunations (synodic months) in a solar year, the period of 12 lunar months (354.37 days) is sometimes referred to as a lunar year.

A common purely lunar calendar is the Islamic calendar or Hijri Qamari calendar. A feature of the Islamic calendar is that a year is always 12 months, so the months are not linked with the seasons and drift each solar year by 11 to 12 days. It comes back to the position it had in relation to the solar year approximately every 33 Islamic years. It is used mainly for religious purposes, but in Saudi Arabia it is the official calendar. Other lunar calendars often include extra months added occasionally to synchronize it with the solar calendar.

The oldest known lunar calendar was found in Scotland; it dates back to around 8000 BC.[1]

Lunisolar calendars[edit]

Main article: Lunisolar calendar

Most calendars referred to as "lunar" calendars are in fact lunisolar calendars. That is, months reflect the lunar cycle, but then intercalary months (e.g. "second Adar" in the Hebrew calendar) are added to bring the calendar year into synchronisation with the solar year. Some examples are the Chinese and Hindu calendars. Some other calendar systems used in antiquity were also lunisolar.

All these calendars have a variable number of months in a year. The reason for this is that a solar year is not equal in length to an exact number of lunations, so without the addition of intercalary months the seasons would drift each year. To synchronise the year, a thirteen-month year is needed 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 occur at the last quarter of the lunar month, as the reproductive cycle of the palolos is synchronised with the moon.[2]

Even though the Gregorian calendar is in common and legal use, lunar and lunisolar calendars serve to determine traditional holidays in many parts of the world, including India, China, Korea, Japan, Vietnam and Nepal. Such holidays include Ramadan, Diwali, Chinese New Year, Tết (Vietnamese New Year), Mid-Autumn Festival/Chuseok and Nepal Sambat and Mongolian New Year as called Tsagaan sar.

Start of the lunar month[edit]

Lunar and lunisolar calendars differ as to which day is the first day of the month. In some lunisolar calendars, such as the Chinese calendar, the first day of a month is the day when an astronomical new moon occurs in a particular time zone. In others, such as some Hindu calendars, each month begins on the day after the full moon or the new moon. Others were based in the past on the first sighting of a lunar crescent, such as the Hebrew calendar.

Length of the lunar month[edit]

The length of each lunar cycle varies slightly from the average value. In addition, observations are subject to uncertainty and weather conditions. Thus to avoid uncertainty about the calendar, there have been attempts to create fixed arithmetical rules to determine the start of each calendar month.

The average length of the synodic month is 29.530589 days. Thus it is convenient if months are in general alternately 29 and 30 days (sometimes 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 ( 1 day after about 2 months)
30 / 1 ( 1 day after about 2 months)
59 / 2 ( 1 day after about 2.6 years)
443 / 15 ( 1 day after about 30 years)
502 / 17 ( 1 day after about 70 years)
945 / 32 ( 1 day after about 122 years; expressible exactly in binary: 11101.10001₂)
1447 / 49 ( 1 day after about 3 millennia)
25101 / 850 ( dependent on change of synodic month value)

These fractions can be used to construct a lunar calendars, or in combination with a solar calendar to produce a lunisolar calendar. A 49-month cycle was proposed as the basis of an alternative Easter computation by Isaac Newton around 1700.[3] The tabular Islamic calendar's 360-month cycle is equivalent to 24×15 months minus a correction of one day.

See also[edit]


  1. ^ http://phys.org/news/2013-07-scotland-lunar-calendar-stone-age-rethink.html
  2. ^ R.H.Codrington. The Melanesians: Their anthropology and folklore (1891) Oxford, Clarendon Press
  3. ^ Reform of the Julian Calendar as Envisioned by Isaac Newton by Ari Belenkiy and Eduardo Vila Echagüe (pdf); Notes and Records of the Royal Society of London (vol 59, no 3, pp. 223-254).

External links[edit]

Original courtesy of Wikipedia: http://en.wikipedia.org/wiki/Lunar_calendar — Please support Wikipedia.
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1412 news items

The Week Magazine
Mon, 21 Jul 2014 11:33:45 -0700

But the Sweden-based non-profit group LunarClock.org has outlined a scheme for a new lunar calendar and Lunar Standard Time that could be used by future moon colonists. A lunar year, equivalent to about 354 Earth days, is broken down into 12 "lunar ...
The Observer (blog)
Tue, 29 Jul 2014 10:48:45 -0700

At the beginning of the week, Muslims celebrated Eid-el-fitr, the feast of ending the fasting of the holy month of Ramadhan. Eid-el-fitr falls on the first day of the month of Shawwal, the tenth month on the Islamic lunar calendar, a calendar is ...
Tue, 29 Jul 2014 08:20:46 -0700

Eid is celebrated once the sighting of a full moon is found, as dictated by a lunar calendar. Syed and Siddiqui aren't the only Muslims to be found on the OU campus. Muslims make up 1.2 percent of the people in Michigan alone, according to the 2000 ...

The Independent

The Independent
Mon, 28 Jul 2014 01:37:30 -0700

Although Eid al-Fitr comes at the end of Ramadan, when Muslims fast from sunrise to sunset, the date is difficult to determine because it is based on the Islamic lunar calendar. The month of Shawwal begins with a confirmed sighting of the new moon ...

Halifax Evening Courier

Halifax Evening Courier
Wed, 30 Jul 2014 05:11:15 -0700

Muslims throughout the world waited in anticipation for the coming of Eid al-Fitr which is determined on the Islamic lunar calendar. In the UK, Eid al-Fitr was recognised on July 28, when it was announced by Saudi Arabia. In Calderdale, congregations ...
Milton Daily Standard
Wed, 30 Jul 2014 05:22:30 -0700

The Vietnamese year is set by the lunar calendar and the date of an event varies from year to year, much as our Easter. Like the Chinese, their calendar begins at the year 2,637 B.C. (1996 was the year 4603). Instead of a 100-year century, the ...

The New Indian Express

The New Indian Express
Tue, 29 Jul 2014 20:11:15 -0700

BHUBANESWAR: Eid-ul-Fitr was celebrated with enthusiasm and fanfare in the Capital City on Tuesday. Eid is celebrated to mark the completion of the holy month of Ramzan. The Muslims follow a lunar calendar and wait for the appearance of full moon to ...
Times of India
Tue, 29 Jul 2014 13:03:45 -0700

NEW DELHI: Eid celebrations at Jama Masjid were muted on Tuesday as people prayed for peace in riot-hit Saharanpur district of Uttar Pradesh. In a break from tradition, the Shahi Imam, Syed Ahmed Bukhari, made a taqrir (speech) before the Eid namaz, ...

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