16 December 2005

North is where the snow is

Looking out my office window the other day, I noticed that the week-old snow was still lingering in almost identical patterns facing the same direction at the bases of the trees lining the median strip of the street. The obvious explanation was that the side of a tree facing north was where snow hadn't melted yet, because that side gets less exposure to the sun. To confirm my hunch, I took my compass and went out for a walk.

The white end of the needle points to north; ignore the red arrow.

This was a common sight throughout the neighborhood.

The compass needle points not to the geographic north, the North Pole, but approximately in the direction of the magnetic north, which is at the present located in Canada.

The red square marks the present location of the magnetic north.

According to a report at the National Geographic News, the magnetic north is moving from Arctic Canada toward Siberia at ~40 km (25 miles) a year and its rate of movement is apparently accelarating. At lower latitudes, and especially when determining on which side of a tree the snow is, the difference between the locations of the magnetic north and the geographic north, the magnetic declination, doesn't make much of a practical difference. But as one gets closer to the North Pole, the magnetic declination must be taken into account for navigational purposes.


afarensis said...

Interesting! It would make a good example of the scientific method in a basic science class.

Henry said...

How fortunate to have both the excellent observation and a camera handy at the same time. I am beginning to suspect that you must keep your camera at hand most of the time.

the Robot Vegetable said...

I find I must carefully account for the 17.5deg declination hereabouts when wandering in the forest on cloudy days.


Yes, I do take my camera with me whenever I go out for a walk unless it is raining or snowing.