Calendopaedia - Astronomical Calendar

Definition of a Year

The most common definition in the western world of the year is based on the revolution of the Earth around the Sun and is therefore called a `Solar Year'. However, there are several possibilities to define beginning and end of one revolution and thus also several kinds of solar years:

The years so defined differ in length because of the precession of Earth's rotation and the tumbling of the Earth orbit.

The Julian year (365.25 days UT) and the Gregorian year (365.2425 days UT) as defined in the calendars of the respective name are solar years as well.

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