In this article we explain how a lunar calendar works, What types of lunar and lunisolar calendars exist, and what they are used for.

What is the lunar calendar used for?

The most widely used calendar in the world, the Gregorian calendar, is a solar calendar system that incorporates months, because it evolved from the Roman calendar, which was lunar. Currently there is no correspondence between the months and the phases of the Moon.

The solar Gregorian calendar is the one in common and legal use in most countries.but traditional lunar and lunisolar calendars are still used around the world to determine many religious holidays and national holidays.

That is why, for example, the dates of Holy Week vary from year to year. Thus, Easter (last day of Holy Week) must be the Sunday immediately after the first full moon after the March equinox.

Other festivities that follow the lunar calendar are the Jewish New Year, the Chinese, Korean, Vietnamese or Mongolian New Year, among others; or the Islamic celebrations of Ramadan, Eid al-Fitr (Feast of the End of the Fast) and Eid al-Adha (Feast of Sacrifice).

A type of lunar calendar, the biodynamic calendar, is also used by farmers to follow different garden tasks based on the lunar phases. Likewise, the biodynamic lunar calendar is also used by many people to know what day it is best to get a haircut or wax according to the lunar phases or even to know what is best to cook taking into account the influence of the moon.

Since when have lunar calendars existed?

There is evidence of a lunar calendar outlined in the cave paintings of Lascaux (France) with 17,000 years old and in a bone staff found in the Le Placard cave, 27,000 years old.

These findings are still controversial, since not all experts agree that the marks correspond to the representation of a lunar calendar.

In any case, historians such as Samuel L. Macey claim that The first uses of the Moon to measure time date back as far as 30,000 years ago.

The Sumerians were probably the first in developing about 6,500 years ago a calendar based entirely on the recurrence of the lunar phases. Each Sumero-Babylonian month began on the first day of visibility of the new moon.

How does a lunar calendar work?

The lunar calendar is essentially similar to the solar calendar. However, since The period of 12 lunations, a lunar year, is 354 days8 hours, 48 ​​minutes, 34 seconds, purely lunar calendars are 11 to 12 days shorter than the solar year.

In these calendars, the lunar months cycle through all the seasons of a solar year over the course of a cycle of 33 to 34 lunar years. The Islamic hijri calendar is an example of a strictly lunar calendar.

How long is a lunar month?

The lunar calendar It is structured by lunations. Since each lunation lasts approximately 29.5 days, it is common for the months of a lunar calendar to alternate between 29 and 30 days.

The duration of each lunar cycle varies slightly from the average value. Furthermore, observations are subject to uncertainty and weather conditions. Therefore, To avoid uncertainty about the calendar, there have been attempts to create fixed arithmetic rules.

The average duration of the synodic month (the time it takes for an object, in this case, the Moon, to reappear at the same point in the sky with respect to the Sun, when observed from Earth) is 29.53059 days.

That’s why, In lunar calendars, months of 29 and 30 days alternate (sometimes called, respectively, «hollow» and «full»).

When does a lunar month start?

The details of when the months start They vary from one calendar to another: some use new, full or crescent moons and others use detailed calculations.

In some lunisolar calendars, such as the Chinese calendar, the first day of a month is given by the astronomical new moon in a particular time zone.

In others, such as some Hindu calendars, each month begins on the day after the full moon. Others are based on the first sighting of the crescent moon, such as the hijri lunar calendar.

Difference between lunar and lunisolar calendar

Most calendars that are described as «lunar» are in fact lunisolar calendars, because their months are based on observations of the lunar cycle, but collation is used (days are added to some months or a month every few years) to bring them into line with the solar year.

Examples of intercalated lunar calendars are the Hebrew or the Myanmar Buddhist calendar, which add a month every two or three years. Other lunar calendars are Chinese, Vietnamese, Hindu and Thai calendars.

A very curious case is the lunisolar calendar adapted to natural phenomena related to the Moon. It is about the banks islands calendarwhich takes into account when edible palolo worms pile up on beaches in the last quarter of the lunar month, since the reproductive cycle of palolos (Palola viridis) synchronizes with the Moon.

Types of lunar and lunisolar calendars

The Chinese calendar

The traditional Chinese calendar is a lunisolar calendar. Although modern-day China uses the Gregorian calendar, the traditional Chinese calendar governs holidays, such as the Chinese New Year and the Lantern Festival, both in China and in Chinese communities abroad.

Also used to select auspicious days for weddingsfunerals, moving or to start a business.

The Hindu calendar

The Hindu calendar or panchanga It is another lunisolar calendar. It is actually a set of calendars with differences in adjusting the lunar and solar cycles, in synchronization with the seasons and in the use of intercalation months and days.

In general, lunar months are counted from new moon to new moon. Ordinary years are 354 or 355 days and leap years are 383, 384 or 385 days.

Gezer Calendar

It is a small limestone tablet with an early Canaanite inscription discovered in 1908 by Irish archaeologist RA Stewart Macalister in the ancient city of Gezer, 20 miles west of Jerusalem. It is commonly dated to the 10th century BC.

Haida calendar

The Haida are an indigenous people, who are divided into two groups, Kaigani (they live on Prince of Wales Island in Alaska) and Haida (they live on the Queen Charlotte Islands, in British Columbia, Canada). Its calendar is divided into two seasons (winter and summer) of six months each, with an occasional thirteenth month between seasons.

Igbo calendar

It is the traditional calendar system of the Igbo people of today Nigeria. The calendar has 13 months in a year (afo), 7 weeks in a month (onwa) and 4 market days in a week, plus an additional day at the end of the year, in the last month.

Islamic hijri calendar

It consists of 12 lunar months in a year of 354 or 355 days. It is used to determine the Appropriate days of Islamic festivals and ritualssuch as the annual period of fasting (Ramadan) and the appropriate time for the Haj (pilgrimage to Mecca). In almost all countries where the predominant religion is Islam, the civil calendar is the Gregorian calendar, but the religious calendar is the Muslim one.

Javanese calendar

It is current in Java along with the Gregorian and Islamic. Although it has fallen into disuse, it is still used for a large number of traditional ceremonies. It uses the same lunar year as the Islamic calendar, but incorporates another indigenous time cycle of 240 days.

Maori calendar (maramataka)

Maramataka means «the spinning Moon» and is the traditional Maori way of counting time. The new year begins with the first new moon following the appearance of the Pleiades (Matariki) on the horizon, in June or July.

Nepali calendar (sambat)

Its origin dates back to the year 2022 BC. On October 25, 2011, the government decided to put Nepal Sambat into use as the country’s national calendar, and created a group to give recommendations on its implementation.

Yoruba calendar

It is used by the Yoruba people of the southwest, center and north of Nigeria and southern Benin. The year begins with the last Moon of May or first Moon of June of the Gregorian calendar. The traditional Yoruba week has four days.

Biodynamic calendar

It is the evolution of the traditional lunarios used by farmers. The biodynamic calendar takes into account the phase of the Moon in relation to the visible constellations and is used in modern biodynamic agriculture to determine the best times to cut wood, plant, harvest or carry out other agricultural tasks. It is also used to choose the best day to get a haircut or wax.