Why are there different types of calendars?



There are many different kind of calendars being actively used around the world and are basically of three types – solar, lunar and lunisolar/solilunar calendars. As the name suggests, a solar calendar is concerned with the Sun, or, more precisely, it is based on the Earth’s rotation around the Sun.

Lunar calendars are based on the rotation of the Moon around Earth and are used mainly for religious purposes, while lunisolar or solilunar calendars combine the two kinds and are

basically solar calendars with dates indicating the moon phase.

The Islamic calendar is a pure lunar calendar with 12 months, each month being either 29 or 30 days. It is counted from the Hijrah, when Prophet Mohammad emigrated from Mecca to Madina, which corresponds to July 16, 622AD. A month starts with the first sighting of the lunar crescent by the human eye after a new moon and each new day begins at sunset.

The Chinese calendar is an example of a solilunar calendar with 12-year cycles, each related to a specific animal, with 12 months in each year and an intercalary month every two to three years. The Hindu calendar which is a lunisolar calendar, starts on Baisakhi, which marks the start of the harvest season.

There are 12 lunar months and each month begins with the new moon before sunrise. There are 29 to 30 days in a lunar month as against 30 to 31 days of a solar calendar and leap years coincide with those of the Gregorian calendar.

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