Jay Gallé: 1 season, 2 beginnings; The difference between the official, unofficial starts of seasons
Wednesday was the last official full day of winter in the Northern Hemisphere, as spring officially arrives late Thursday morning at 11:57 a.m. CST.
Unofficially, spring arrived March 1, and will last until May 31, when the “meteorological” or “climatological” start of summer occurs on June 1.
But the “astronomical” start of summer doesn’t arrive until June 21.
Why the lag and different start times?
The two beginnings of each season have to do with how the seasons are scientifically governed and how we humanly express them.
As we move through the seasons, the sun’s rays are migrating across the globe from pole to pole with the most intense sun occurring in the summer and least in the winter.
The official start of any season is tied to the sun and how its rays strike the earth; or more accurately, when the sun’s rays strike the Earth at a perpendicular angle.
For spring, this usually occurs between March 19 and 21 when the sun’s perpendicular rays strike the Earth at the equator. It’s also the reason spring is known as the spring equinox.
The word equinox is Latin for “equal night” and it is called so because the length of daylight and nighttime are equal and roughly 12 hours each.
The same phenomenon occurs in September during the autumnal equinox except the sun’s perpendicular angle is traveling toward the South Pole as opposed to the northern path toward the North Pole in the spring and summer.
It all can be a little confusing, and to make matters worse, all of the above applies to the northern hemisphere and is reversed in the southern hemisphere.
Whereas, summer in the northern hemisphere means it is winter south of the equator.
That’s why we humans like to keep it simple when we can, and why we get the meteorological / unofficial start of the seasons.
All wrapped in tidy, easy to understand packages are our four “meteorological” seasons beginning and ending at the same time every year in easy to remember three-month sections that are relative approximations of the actual, official, “astronomical” seasons.
So when summer rolls around June 1, don’t be surprised if it doesn’t feel quite like summer because remember, it really hasn’t started yet -- it’s just easier and more convenient for us to say it has.
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