equinox

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[Earth]

Meteorological vs Astronomical Spring

Meteorological Spring and Astronomical Spring are two ways of defining the start of spring, but they are based on different criteria. Meteorological Spring refers to the three calendar months of March, April, and May in the Northern Hemisphere (or September, October, and November in the Southern Hemisphere). These months are considered to be spring because they generally have milder temperatures and more rainfall than the preceding winter months, and the days start to become longer.

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[Sky]

Astronomical Spring

March 20 is the day of the vernal equinox, after which the length of the day will gradually become longer than that of the night. On the equinox day the Sun will cross the celestial equator and equalize day and night. That will start an astronomical spring in the northern hemisphere.

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