Even as the bitter chill returned this week, reminding everyone that winter is upon us, there was a light at the end of the, no, not the tunnel, the light was at the end of the day. Take a peek out the window as the clock ticks toward 5 p.m. Just a couple of weeks ago, you would have been greeted by the total darkness of night. Now there’s a glimmer of light a little before 5 p.m., though the sun has officially set.

Minute by minute, daylight is creeping back, in a cycle that is as old as time. On the winter solstice, Dec. 22, we enjoyed just 8 hours and 38 minutes of daylight. Officially that’s the shortest day of the year, but in reality, the Northwoods received just 8 hours and 38 minutes of daylight each day for a whole week, from Dec. 18-25. That’s when the sun appears farther south in the sky than any other time of the year. Then it begins its annual journey back north.

The day is now several minutes longer than it was during that darkest week. None of the lengthening has come in the morning. The sun rose at 7:35 a.m. Dec. 22, and remained the same as the week progressed. The lengthening has all come in the evening, and we’re beginning to notice. It hints beguilingly at what’s to come. By the end of January; the day will begin to stretch out at both ends, with sunrise at 7:04 a.m. and sunset at 5:04 p.m.-a full 9 hours 38 minutes of daylight. By the summer solstice (June 20 this year), we’ll reach the maximum 15 hours and 5 minutes of sunlight. Then, continuing this age-old cycle, the sun once again will begin to sink south in the sky. It’s a useful reminder that glimmers of more light coming, even on these dark days, and darkness begins to fall earlier, even when the days seem endless.

What makes the world turn? Is it the gravitational tug of the moon? Our planet doesn’t rotate because of something that’s happening now. Something set it going eons ago, and though it’s gradually slowing down, it’s got many more eons to go before it stops. What kind of something? Here’s the leading theory:

The solar system formed out of dust and gas left over from the making of the sun. Little chunks of matter gradually gathered into bigger chunks, as gravity worked its magic. Eventually, about 4.5 billion years ago, a very large chunk-the size of Mars-is thought to have collided with Earth.

“It was really a titanic collision,” says Luke Dones of NASA’s Ames Research Center. “It hit off-center, so it set Earth spinning.”

Some of the debris from this collision, incidentally, is believed to have been thrown into orbit, forming our moon. Earth really got to twirling after that collision, a day might have been as short as four hours. Since then, the pace has slowed considerably because of a process known as “tidal friction.” The tides, of course, occur when the moon’s gravity raises a bulge in the ocean. To oversimplify a bit, the moon tries to hold onto the bulge, while Earth’s rotation tries to move it away, with the net effect that Earth turns a little slower (and the moon revolves around it a little faster) with each rotation. The slowdown isn’t what you’d call drastic-only a few thousandths of a second per century-but forewarned is forearmed: Eventually there’s going to be a day that lasts forever. What do you want to bet it’s a Monday?

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And now a bit of humor”

God is talking to an angel about creating the world. “I just made a 24-hour period,” God explains. “It will be half-light and half-dark, and it will keep repeating itself until the end of all time.”

“Wow,” says the angel. “What are you going to do next?”

“Well, I’m tired. I think I’ll call it a day.”

Peter Dring is a retired nature biologist and phenologist who lives in the Land ‘O Lakes area. Questions or comments for Dring can be sent to star [email protected].