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's orbit around the sun. During summertime, our planet's north pole points mildly toward the sun and those of us in the northern hemisphere get more than 12 hours of sunlight. During the winter 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've been thinking about sunlight, in part, because I dislike losing it so rapidly this time of year, but, in part, because the sun has garnered some media attention since its poles are reversing. That's right, its magnetic poles are in the process of flipping. Here's the scoop:
The sun has two big cycles of change. First, the number of sunspots - dark regions on the surface of the sun - wax and wane over time. That's something you may have once learned in science class. But another cycle that's 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's magnetic field is in the process of decaying to zero. In the coming weeks it will reorganize itself with north and south poles fully reversed.
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 said to me. "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 - it's a show you don't ever forget if once you see a really good example of it.
Variations in the sun's 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.
Enjoy the warmth of the sun's rays as much as you can in the coming days. We won't 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.