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. It uses both the Moon's monthly cycles and the solar year to keep track of time.

Because the Moon's cycles don't match perfectly with Earth's year, most lunisolar calendars have twelve months in a year. But every few years, they add an extra month. This extra month helps keep the calendar in line with the seasons.

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

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 mix the moon's cycles with the sun's year. Some of these calendars, like the Chinese, Coligny, and Hebrew ones, help us know the seasons. Others, like the Buddhist and Hindu calendars, help us know when the full moon happens.

Chinese lunisolar calendar

Main article: Chinese calendar

The Chinese calendar is also called the farming calendar or yin calendar because it uses both the sun and the moon to track time. It has been used for thousands of years, with records going back to around 1050 BC. It has changed over time, but it is still used today with 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 comes from this calendar, giving each year an animal 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 way to decide the date of Easter and other holidays that change each year. They watch the Moon. They look at a special full Moon after the spring equinox in March. This helps them choose the date. This full Moon is close to the real one, but not exactly the same. Eastern Christian churches use a similar way, but they follow the Julian calendar instead.

Reconciling lunar and solar cycles

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

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

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