Most of the Northern Hemisphere will celebrate the beginning of spring in mid-March, but if you notice meteorologists breaking out the party hats and confetti early, there is a reason why.
The spring equinox in the Northern Hemisphere will fall on March 19 at approximately 10:06 p.m., according to NASA.
For meteorologists, the start of spring will be coming much sooner than that. In fact, the start of meteorological spring will fall on Friday in the eyes of those that study the weather.
The reason meteorologists have a different definition for spring is simple: the date never changes. Unlike astronomical spring, which doesn’t fall on the same date every year, the changing of the seasons for meteorologists always fall on the same dates. Winter begins on Dec. 1, spring begins on March 1, summer begins on June 1, and fall begins on Sept. 1.
That ensures consistency in recordkeeping, and just about mirrors the changing of the seasons in terms of temperatures and weather conditions.
The reason astronomical spring changes dates is because the Earth doesn’t take exactly 365 days to orbit the sun. In fact, the common wisdom is that it takes 365 and one-quarter days, which is why we have leap years, but that measurement isn’t precise either, leading to the seasons changing date very slightly each year.
Astronomical spring begins when the sun crosses the celestial equator, moving toward the Northern Hemisphere as opposed to the Southern Hemisphere.
Local
As a reminder to Chicago residents, the start of astronomical spring does not mean that the city will receive 12 hours of daylight and 12 hours of night. That date will actually fall on March 17, when Chicago will receive more than 12 hours of daylight, according to NASA.
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