Oct 03 2011
Incredible as it seems, the dotted blue line on this map is moving north.
That line is the Arctic Circle which defines the northern region on Earth that experiences at least one 24-hour day in summer and one 24-hour night in winter.
I thought the Arctic Circle was permanent so I was stunned to find out last weekend that it’s moving north 49 feet (15 meters) per year. The area inside the circle is shrinking — and it’s basically the moon’s fault.
The Arctic Circle moves because the earth wobbles on its axis. This happens for a variety of reasons but the biggest contributor is the tidal force caused by the moon’s gravitational pull. The result is a 2o change in the earth’s tilt over a 41,000 year period.
Right now the earth’s tilt is becoming less pronounced and the axis is slowly becoming upright. Inch by inch, the North Pole is facing the sun less than it did the day before and locations on the edge of the Circle are losing the midnight sun by 49 feet per year.
In practice this is far less noticeable than it sounds because atmospheric refraction bends the light and topography allows us to see the sun longer from mountaintops.
Besides, it’s happening very slowly. I don’t know when this particular wobble began its upward tilt nor when it will pause and start back down but with a 41,000 year period I don’t expect to see it in my lifetime.
(image in the public domain from Wikimedia Commons. Click on the image to see the original.)