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Tuesday, May 31, 2011

Now is the winter of our discontent

Would you believe today is the first day of winter. If you're in the northern hemisphere, you might be thinking: "Do not be a fool Noah, the sun is shining. Summer is about to start." Those of you who know we're in New Zealand might be thinking something like: "One would think winter starts on June 21st...you fool." Hey, quit trying to spread your American Imperialist ideas down here. Winter starts today, and that's final. Also, I'm really cold.

In astronomical reckoning, the solstices and equinoxes ought to be the middle of the respective seasons, but, because of thermal lag, regions with a continental climate often consider these four dates to be the start of the seasons as in the diagram, with the cross-quarter days considered seasonal midpoints. The length of these seasons is not uniform because of the elliptical orbit of the earth and its different speeds along that orbit.

From the March equinox it takes 92.75 days until the June solstice, then 93.65 days until the September equinox, 89.85 days until the December solstice and finally 88.99 days until the March equinox. In Canada and the United States, the mass media consider the astronomical seasons "official" over all other reckonings, but no legal basis exists for this designation.

Because of the differences in the Northern and Southern Hemispheres, it is no longer considered appropriate to use the northern-seasonal designations for the astronomical quarter days. The modern convention for them is: March Equinox, June Solstice, September Equinox and December Solstice. The oceanic climate of the Southern Hemisphere produces a shorter temperature lag, so the start of each season is usually considered to be several weeks before the respective solstice or equinox in this hemisphere, in other countries with oceanic climates, and in cultures with Celtic roots.

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