Spring 2021 will arrive at 5:37 a.m. Saturday, March 20, which is squarely in the middle of the range of days on which it can fall, March 19, 20 or 21.
The first day of spring is also known as the vernal equinox.
Spring and fall begin at an equinox, while summer and winter begin at a solstice.
At the equinox, the tilt of the Earth is zero relative to the Sun, and the northern and southern hemispheres receive about equal amounts of the Sun’s rays. For someone standing on the equator, the Sun would pass directly overhead on the equinox.
A solstice happens when the Sun appears to reach its most northerly or southerly points in the sky. Here, in the northern hemisphere, summer begins when that northerly mark is reached, and winter begins when that southerly mark arrives.
The dates for all those events vary because Earth makes a full orbit of the sun every 365.24 days, which leads to our seasons varying from 89-93 days. That’s also why our calendar adds an extra day every 4 years, giving us our leap years.
The astronomical start of spring can fall on March 19, 20 or 21, although we won’t see another March 21 equinox in the continental U.S. until 2101.
Because of that variation, meteorologists view the first day of spring every year as March 1. By marking the start of each season on the same date each year, they build in more consistency in comparing climatological statistics from one year to the nest.
Contact Marcus Schneck at mschneck@pennlive.com.
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March 01, 2021 at 05:03PM
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When is the first day of spring? - pennlive.com
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