Oct 03 2011

Moving North

Published by at 7:15 am under Musings & News

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.)

3 responses so far

3 Responses to “Moving North”

  1. Kathyon 03 Oct 2011 at 9:52 am

    Kate, this is true. Tampa International Airport had to remark its runways due to this gravitaional pull also!

    http://www.cfnews13.com/article/news/2011/january/191834/FAA-orders-Tampa-airport-to-redo-markings?cid=rss

  2. Kate St. Johnon 03 Oct 2011 at 10:27 am

    It’s even more incredible than that! It turns out that the earth’s magnetic field is not much related to the location of it’s rotational axis. The magnetic field moves around on its own and has been known to shift completely so that “the Earth’s magnetic field reverses itself every million years or so (the north and south magnetic poles switch).” !Yow!

    Read more here at this Physics Dept web page at Univ of Tennessee at Knoxville:
    http://csep10.phys.utk.edu/astr161/lect/earth/magnetic.html

  3. Kathyon 04 Oct 2011 at 7:34 am

    That is wild! On a lighter side…I was just thining of how I explain to the Grandkids that Santa’s reindeer have to learn the reverse route.

    It’s the kid in me, Kate. Sorry……

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