Lunisolar calendar

A lunisolar calendar is a special kind of calendar that mixes together the phases of the Moon with the passing of the Earth's orbit around the Sun. This means it uses both monthly lunar cycles and the solar year to keep track of time. Because the Moon's cycles don't perfectly match up with the Earth's year, most lunisolar calendars have twelve months in a year. But every few years, they add an extra month, called an embolismic year, to keep the calendar in line with the seasons.

Lunisolar calendars are used in many different cultures around the world. Unlike purely lunar calendars, such as the Islamic calendar, lunisolar calendars have special rules to add extra months. This helps make sure that the calendar stays connected to the changing seasons throughout the year.

Examples

The Chinese, Buddhist, Burmese, Assyrian, Hebrew, Jain, traditional Nepali, Hindu, Japanese, Korean, Mongolian, Tibetan, and Vietnamese calendars, along with the ancient Hellenic, Coligny, and Babylonian calendars, all use a lunisolar system. This means they combine the cycles of the moon with the solar year. Some of these calendars, like the Chinese, Coligny, and Hebrew ones, help us understand the seasons, while others, like the Buddhist and Hindu calendars, help us know where the full moon is in the stars.

Chinese lunisolar calendar

Main article: Chinese calendar

The Chinese calendar is also known as the farming calendar or yin calendar because it uses both the sun and the moon to keep track of time. It has been used for thousands of years, with records dating back to around 1050 BC. Over time, it has been improved and changed, but it is still used today alongside the solar calendar. Important holidays like Chinese New Year, Lantern Festival, Mid-Autumn Festival, and Dragon Boat Festival are based on this calendar. The Chinese zodiac also comes from this calendar, assigning an animal to each year in a twelve-year cycle.

Movable feasts in the Christian calendars, related to the lunar cycle

The Gregorian calendar is the calendar most people use today, but Western Christian churches use a special method based on the Moon to decide the date of Easter and other special holidays that change each year. They look at a special full Moon that comes after the spring equinox in March to set the date. While this is close to the real full Moon, it is not exactly the same. Eastern Christian churches use a similar method, but they follow the Julian calendar instead.

Reconciling lunar and solar cycles

A tropical year is about 365.2422 days long, and a lunar month is about 29.5306 days long. This means a year has roughly 12.36826 lunar months, so a typical year of 12 months needs an extra month every few years to match up with the solar year.

Many lunisolar calendars add a leap month every 2 to 3 years. One common way to decide when to add this leap month is the Metonic cycle, which adds 7 leap months in every 19 years. This method was used by the Babylonians and is still used today in some calendars.

List of lunisolar calendars

Here is a list of different lunisolar calendars from around the world, grouped by their families:

• Babylonian calendar family
  • Ancient Macedonian calendar
  • Hebrew calendar
  • Umma calendar
• Hindu calendar family
  • Vikram Samvat
  • Buddhist calendar
  • Burmese calendar (Pyu calendar)
    • Chula Sakarat
  • Nepal Sambat
  • Thai lunar calendar
  • Vira Nirvana Samvat (Jain calendar)
• Chinese calendar family
  • Japanese calendar
  • Korean calendar
  • Mongolian calendar
  • Tibetan calendar
  • Vietnamese calendar
• Unclassified or independent
  • Attic calendar
  • A lunisolar calendar created by Plethon
  • Ptolemic Egyptian calendar
  • Inca calendar
  • Celtic calendar, including Coligny calendar
  • Muisca calendar
  • Nisg̱a'a calendar
  • Old Eastern Ojibwe calendar