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Difference Between Lunar and Solar Years

A picture of a crescent and the Sun

The definition of a solar year is referenced to the sun, whereas a lunar year is referenced to the movement of the moon. Since time immemorial, mankind has used the movements of the sun and the moon to break time into smaller portions. We have broken down vast time into millennia, centuries, decades, years, months, etc. Depending on which part of the world you are, you will be using the lunar or solar years or their combination. Solar years are longer than lunar years by 11 days. The term “epac” describes this time difference between a solar year and a lunar year, i.e. 11 days.

A lunar year is made up of 12 lunar months. A lunar month can also be defined as the time the moon takes to pass through each of its phases (new moon, half-moon and full moon) and return to its original position. A lunar month takes an average of 29.5 days.

What is a Solar Year?

The length of time required for Earth to complete one revolution around the sun is defined as a solar year.  Consequently, a solar month means one twelfth of a solar year. Gregorian months differ slightly from this, as the number of days in each month are not the same. But this is often overlooked, as the sum total of days are always the same.

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What is the Duration of a Lunar and a Solar Year

There is approximately 354 days in a lunar year. A solar year on the hand has 365 days. This leaves an 11-day difference between one solar year and one lunar year, resulting from the difference in their definitions. This difference of 11 days is termed epac. When about 33 years of time has passed, a full year will exist between the users of solar years and lunar years. Because there is an 11-day difference between a solar year and a lunar year, some users of the lunar calendar insert an extra (13th) month into it every three years. Other users do not. Users of the solar calendar add an extra day every four years. In those years, the total number of days in February changes from 28 to 29.

Who Uses the Lunar and Solar Calendars?

In modern times, the majority of people of the world uses the solar calendar. However, Muslims and Jews and some African civilisations follow the lunar calendar. Islamic calendars, also known as Hijri calendar, is a type of lunar calendar consisting of 12 lunar months. The Hijri calendar is essential in the observance of religious periods such as Ramadan, Hajj (pilgrimage to Mecca) and other Muslim religious festivals. The Jewish calendar is slightly different. Each month begins when a new crescent is sited, but Jewish years are still based on solar definitions. Chinese calendars use a combination of lunar and solar calendars. It is therefore termed lunisolar calendar.


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