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Vernal Equinox also known as the The Northward equinox (or March equinox) is the equinox on the earth when the Sun appears to cross the celestial equator, heading northward. The Northward equinox is the vernal equinox in the Northern Hemisphere and the autumnal equinox in the Southern Hemisphere.
The equinox can be as early as March 19 or as late as March 21, the precise time being about 5 hours 49 minutes later in a common year, and about 18 hours 11 minutes earlier in a leap year, than in the previous year. It is the balance of common years and leap years that keeps the calendar date of the equinox from drifting more than a day from 20 March each year.