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Definition:
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The duration of the Earth's revolution round the Sun, forming a natural but slightly variable unit of time. In glaciology, as in other disciplines concerned with the natural progression of the seasons, the year may vary in length for reasons of necessity or convenience, and depending on whether the particular investigation requires precise treatment of calendar time. In mass-balance practice the year is always either exactly or approximately 365 calendar days long (the duration of a calendar year which is not a leap year. However the sidereal year is very nearly equal to 365.2564 mean solar days. In turn, the mean solar day is very nearly equal to 86 400 seconds, and 1 day is defined in the Syst
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