year, time required for the earth to complete one orbit about the sun. The solar or tropical year is measured relative to the sun and is equal to 365 days, 5 hr, 48 min, 46 sec of mean solar time (see solar time). The sidereal year, measured relative to the stars, is longer than the tropical year by about 20 min. The calendar year is used for practical purposes and always contains a whole number of days, the ordinary year being 365 days and the leap year 366 days.
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