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The Spring Equinox Is Here, One of the Most Equally Divisive Days on the Planet

The sun sets due west on the spring equinox, set for March 20, 2022. (Patty Wetli / WTTW News) The sun sets due west on the spring equinox, set for March 20, 2022. (Patty Wetli / WTTW News)

Maybe it feels like the arrival of spring has already been celebrated a time or two this month, but the official start of astronomical spring takes place Sunday at 10:33 a.m.

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That’s when the vernal equinox is set to occur: Along with the fall equinox, it’s one of two days in the year when the sun is directly over the equator and earth is divided into equal halves of dark and light.

Picture a straight vertical line running from the North Pole to the South Pole, splitting the planet in two. This line is called the “terminator,” and with the exception of the fall and spring equinoxes, it’s tilted to provide less daylight to either the northern or southern hemisphere.

Here’s what the shifting terminator looks like from space, as captured by a NASA satellite. The 12-second timelapse video begins during an autumnal equinox and runs through an entire year of seasonal changes.


And here’s a more colorful variation.


Equinoxes are always extra special in Chicago, thanks to the city’s grid. The sun rises due east and sets due west on the equinox, creating a phenomenon known as “Chicagohenge“ (in reference to Stonehenge), when the sun is strikingly framed by the city’s skyscrapers. The Chicagohenge effect is most apparent downtown, but it can be appreciated from any east-west street, and lasts for a couple of days after the equinox. 

Contact Patty Wetli: @pattywetli | (773) 509-5623 |  [email protected]

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