Officially, the equinox is today, but the actual crossover doesn’t take 24 hours. Strictly speaking, day and night aren’t precisely 12 hours long.
Daylight duration has been getting shorter since the summer solstice on June 21 started the season. All summer long, the earth was in a position where its northern half, where we’re located, leans toward the sun. Now we’ll see more darkness hours than daylight until March 20. On that day, the pattern will reverse again.
At first glance, it may look like June 21 and Sept. 23, summer’s boundary dates, are out of sync with the climate. After all, we have the hottest days of the year in August, eight weeks after the summer solstice, and it’s still very warm now in September.
The reason for the long lag time is the fact that we live on an ocean planet, with 71 percent of the world covered by ocean water. The world’s oceans take weeks to warm up or cool.
Inland locations, especially deserts, adjust quickly to changes in sunlight. Some deserts, hot during daytime, even freeze at night. But the southeastern edge of Georgia borders on the Atlantic Ocean, so the warm weather can remain longer in the fall than at locations farther inland.
We won’t notice much seasonal temperature change right away after today. But plants know when the equinox happens. Their cycles of growth, flowering and fruit production depend on the length of daily sunlight, not on temperature. Chrysanthemums and poinsettias, for example, prefer short days. The equinox marks the time when they get on the gardener’s agenda.
Sometimes a question comes up about the relationship between equinoxes and climate change. The so-called precession of the equinoxes has been known for a long time. The earth isn’t a sphere. It resembles a medicine ball, slightly flattened at the top and bottom. This causes a wobble, which in part is responsible for the Ice Ages. There were five that we know about, going back thousands to millions of years. As far as the current climatic changes due to increased CO2 in the atmosphere are concerned, there is no connection to the solstices and equinoxes.
Rudi Kiefer, Ph.D., is a professor at Brenau University, teaching physical and health sciences on Brenau’s Georgia campuses and in China. His column appears Sundays and at gainesvilletimes.com.