Year

A year is the time between two recurrences of an event related to the orbit of the Earth around the Sun. By extension, this can be applied to any planet: for example, a "Martian year" is a year on Mars.

Calendar year

A calendar year is the time between two dates with the same name in a calendar.

Related Topics:
Calendar year - Calendar

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Solar calendars usually aim to predict the seasons, but because the length of individual seasonal years varies significantly, they instead use an astronomical year as a surrogate. For example, the ancient Egyptians used the heliacal rising of Sirius to predict the flooding of the Nile.

Related Topics:
Solar calendar - Ancient Egypt - Heliacal rising - Sirius

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The Gregorian calendar aims to keep the vernal equinox on or close to March 21; hence it follows the vernal equinox year.

Related Topics:
Gregorian calendar - Vernal equinox - March 21 - Vernal equinox year

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No astronomical year has an integer number of days or months, so any calendar that follows an astronomical year must have a system of intercalation such as leap years.

Related Topics:
Intercalation - Leap year

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In the formerly used Julian calendar, the average length of a year was 365.25 days. This is still used as a convenient time unit in astronomy, see below.

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