As we hit St. Patrick’s Day, spring is right around the corner in the Northern Hemisphere, even if it doesn’t feel like it judging by Chicago’s forecast.
Spring will get underway, at least from an astronomical perspective, later this week, according to the National Weather Service.
In fact, we even know the precise time when spring begins: 10:06 p.m. Central Daylight Time on Tuesday.
The reason we know the exact date is because the spring equinox marks a precise moment in time on the Earth’s revolution around the sun. As the planet moves, it does so at an angle, meaning that its axis is either tipped away from, or towards, the sun.
During fall and winter in the Northern Hemisphere, the Earth’s axis is tilted away from the sun, meaning that the Southern Hemisphere experiences more sunlight and therefore warmer conditions and longer days.
On the spring equinox, the planet’s axis makes the transition to being tilted toward the sun, meaning that the Northern Hemisphere gets the warm weather treatment.
While the common conception is that each hemisphere receives equal daylight and night time on the equinox, that’s not precisely true because of the inexact nature of our solar-based calendar. As a matter of fact, according to TimeandDate’s sun graph, the city of Chicago will actually receive just over 12 hours of daylight on Sunday, the first time we’ve hit that milestone since Sept. 25, 2023.
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None of this holds true for meteorologists, however. That’s because “meteorological spring” officially began on March 1, a method used for ease of recordkeeping and comparison.
For those curious when summer will begin, the NWS has that information as well, with the season officially beginning at 3:51 p.m. on June 20.
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