The eclipse was fun to watch last Monday. Yet even with our world getting darker for a short while, events of this kind don’t make much of an impact on our natural systems. Much more dramatic is the effect of the earth’s orbit around the sun.
It takes us 365 days and six hours to complete one circuit. Because the earth’s axis is tilted, we experience huge seasonal climate changes. Currently we’re heading toward the Sept. 22 equinox, when both hemispheres receive equal amounts of sunlight.
This will end the time during which our northern half of the globe was leaning toward the sun, spending more time in the sunlight (daytime) than in the shade (nighttime). The equinox brings the end of summer and the beginning of fall. Starting in late September, nighttime will be more dominant in North Georgia than daylight.
At the same time, you’ll notice that the sun doesn’t rise as high in the sky anymore. In the afternoon, it seems to be more and more eager to disappear at the southwestern horizon. Commuters traveling from Gainesville to Oakwood, Buford and beyond will notice this as a traffic hazard. Interstate 85 goes southwest toward Atlanta, and driving there late on a clear fall afternoon means heading directly into the blinding light of the setting sun.
It can be worse on roads like Peachtree Industrial Boulevard, which takes the same direction, but the trip is interrupted by numerous traffic lights. In blinded conditions, it’s hard to see what color they are.
With less sunlight available, the North American land mass is cooling quickly. Cold air settling down on the ground during the lengthening nights begins to spread over the continent. We’ll see its edge coming to Georgia with a forceful push toward the end of October.
The arrival of this edge in the form of cold fronts makes Nov. 1 the average first frost date in Hall County. The www.plantmaps.com website provides detailed information on this for gardeners and farmers.
As the calendar progresses, the earth’s orbit reaches the darkest day of the year, and the longest night: Dec. 21. Beyond that date, the continent cools for six more weeks until we hit the coldest time in North Georgia. On March 20, another equinox starts the period of more daylight than nighttime, and plentiful sunshine returns to North Georgia.
Rudi Kiefer, Ph.D., is a professor of physical science and director of sustainability at Brenau University. His column appears Sundays and at gainesvilletimes.com.