As an aging citizen of Scandinavian descent, I dread this time of year. Each evening the sun sets significantly earlier. Deep in the bones of us northern people is the notion that summertime is the season of life and hope while winter is, well, cold and horribly dark.
This week all of the globe enjoys roughly 12 hours of sunlight and 12 hours of night. The “reason for the season” relates to the Earth‚Äôs orbit around the sun. During summertime, our planet‚Äôs north pole points mildly toward the sun and we in the northern hemisphere get more than 12 hours of sunlight. During the winter the Earth has traveled halfway around its orbital path. At that time, the north pole is pointed away from the sun and the southern hemisphere enjoys more sunlight while we northerners shiver in the dark. Now, at the start of fall, we stand at the in-between time.
I‚Äôve been thinking about sunlight in part because I dislike losing it so rapidly this time of year, but in part because the sun has been in the news, too. The reason our favorite star has garnered some media attention is that its poles are reversing, north to south.
Here‚Äôs the scoop:
The sun has two big cycles of change. First, the number of sunspots ‚Äî dark regions on the surface of the sun ‚Äî wax and wane over time. That‚Äôs something you may have once learned in science class. But another cycle that‚Äôs less well known is that the magnetic poles of the sun swap places, north to south. Both of these changes occur on a cycle of about 11 years.
I recently talked about the sun to Dr. Michael Allen, a colleague of mine in the Department of Physics and Astronomy at Washington State University. Allen explained to me that the sun‚Äôs magnetic field is in the process of decaying to zero. In the coming weeks or months it will next reorganize itself with north and south poles fully reversed.
“It‚Äôs not surprising that the sun has cycles,” Allen said. “But our sun is pretty darn stable compared to other stars.”
That stability may have played a part in making it possible for earliest life to get off the ground and go to town.
“But that‚Äôs really quite speculative,” Allen said.
What was the north pole of the sun has actually already become a south pole. That means that at the moment the sun has two south poles.
“Presumably that configuration is unstable,” Allen explained. “It will likely change soon and the poles will be fully reversed.”
The changes the sun is going through mean the sun is producing more cosmic rays. That translates into more impressive shows of the Northern Lights (Aurora Borealis) which you may see lighting up portions of the night sky on clear nights. Once, riding sleepless on a Greyhound bus across North Dakota I saw the whole night sky lit up by the Northern Lights ‚Äî it‚Äôs a show you don‚Äôt ever forget if once you see a really good example of it.
But there‚Äôs an important point about the sun‚Äôs cycles that goes beyond entertaining light shows. Variations in the sun‚Äôs output of heat that goes along with changing numbers of sunspots appears to be one factor that can change climate here on Earth. The 11-year solar cycle, for example, shows up in the evidence of tree ring widths in the American Southwest, presumably because the solar cycle is a factor controlling precipitation.
“The link to climate is speculative but also potentially very important,” Allen said. “I knew you‚Äôd ask me about it,” he added with a laugh.
To measure how much solar energy is actually absorbed by the Earth over time, NASA developed the Deep Space Climate Observatory (DSCOVR). It‚Äôs designed to stay between the Earth and the sun, always “looking” at the sunlit side of the Earth and measuring energy absorption over time and in different regions.
The satellite was actually built long ago, but it‚Äôs been warehoused rather than launched due to political and budgetary issues, Allen explained.
Enjoy the warmth of the sun‚Äôs rays as much as you can in the coming days. We won‚Äôt see this much daylight again until March.
Dr. E. Kirsten Peters, a native of the rural Northwest, was trained as a geologist at Princeton and Harvard. This column is a service of the College of Agricultural, Human and Natural Resource Sciences at Washington State University.