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By this time tomorrow, it will be spring. The spring or vernal equinox occurs at 12:50 a.m. ADT Friday (1:20 a.m. NDT). At that time, the Earth will reach the point in its orbit where its axis isn’t tilted toward or away from the sun. The sun will then be directly over a specific point on the Earth’s equator moving northward.
I often get asked when the spring equinox stopped taking place on March 21. It’s true that when I was in grade school, we were told the first day of spring was on March 21, not March 20, and as will be the case in time zones east of us, certainly not March 19!
And if it seems even earlier this year, you’re right! This is the earliest the vernal equinox has occurred in 124 years. It’s the first year since 1896 where the equinox occurs on March 19, rather than 20 or 21, for all time zones west of the Atlantic Time zone.
The equinox is determined by the sun’s location; the equinox time is when the sun is directly over the celestial equator. There are several factors to account for the date shift, including the precession or “wobble” of the Earth’s axis and the pull of gravity from the other planets, which – ever so slightly – affects the location of the Earth in its orbit.
We can add another variable to this year’s equinox equation – leap year. Because of the leap year, the equinox is almost 18 hours ahead of last year’s occurrence.
Interestingly, in the Northern Hemisphere, spring is currently being reduced by approximately one minute per year and winter by about one-half minute per year. Winter is the shortest astronomical season. With its seasonal duration continuing to decrease, it is expected to attain its minimum value of 88.71 days by about the year 3500.
If you’re waiting for spring to arrive on a March 21, you’ll be waiting a while. Here in North America, throughout the entire 21st century, the equinox will arrive no later than March 20.
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Cindy Day is the chief meteorologist for SaltWire Network