Today is the first day of Spring in the Southern Hemisphere.
And it’s also not the first day of Spring.
Wait. What?
There are two first days of Spring, depending upon which definition you use.
September 1st is the first day of Meteorological Spring.
September 22nd is the first day of Astronomical Spring (sort of, anyway; see below).
Meteorological seasons revolve around what’s happening with the weather on Earth, primarily viewed through temperature cycles, while Astronomical seasons are based on what’s happening in space and where the sun is relative to the Earth.
So yes, today is the first day of Spring here in South Africa… if you’re using the Meteorological Calendar.
And why would you do that? Well, the National Oceanic and Atmospheric Administration has a few good reasons:
Meteorological observing and forecasting led to the creation of these seasons, and they are more closely tied to our monthly civil calendar than the astronomical seasons are. The length of the meteorological seasons is also more consistent, ranging from 90 days for winter of a non-leap year to 92 days for spring and summer.
By following the civil calendar and having less variation in season length and season start, it becomes much easier to calculate seasonal statistics from the monthly statistics, both of which are very useful for agriculture, commerce, and a variety of other purposes.
Those are good reasons. But then they came from a meteorologist’s point of view. If we’re looking for a (possibly) less arbitrary, but more variable and difficult to use system, we still have another 3 weeks of winter – which seems entirely plausible, because despite what the so-called “temperature cycles” are supposed to be doing, it’s still very chilly here.
What happens during the September Equinox?
This:
During the September Equinox, the sun switches sides from the northern hemisphere to the southern hemisphere of the earth. That’s why the September equinox is also known as the Southward Equinox.
…and that Southward Equinox marks the start of (Astronomical) Spring.
In conclusion:
The official start of Spring this year is the 22nd September.
Although because of that late evening solstice, the first day of Spring in Cape Town will actually be the 23rd September.
Oh, and it’s also today.