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True North versus Magnetic North:

True North is what is commonly thought of as the North Pole. Looking at a globe, true North would be at the very top, in the middle of an icy continent. True North never changes over time.

Magnetic North is more complicated. The Earth is not a simple solid magnet. Scientists believe that the Earth's magnetic field comes from its liquid core. The liquid core moves and generates electrical currents, and these currents create the Earth's magnetic field. Since the core is liquid, the core itself and its electrical currents change over time. This causes the Earth's magnetic field to change slowly, and we can observe this change by looking at historical positions of Magnetic North.

The North magnetic pole is in Canada! Early explorers started measuring the position of the pole in 1831. In recent years, Canadian Government scientists have measured the position of the pole every few years. The maps below show how much the pole has moved

The North magnetic pole has been moving an average of 10km per year over the last century! Today, the magnetic pole is located somewhere near Ellef Ringnes Island, in Canada's far North. The pole is always moving, but it moves slowly enough that it only needs to be accurately measured for maps or charts every few years.

Maps and Charts:

Maps and charts always use true North as their reference point. All of the latitude and longitude lines (maps and charts use lines of latitude and longitude to give us a way to express location) on a map or chart are drawn in relation to true North. The longitude lines (which are drawn North-South) all converge at the true North Pole.

So what good is a magnetic compass? The problem is magnetic compasses always point to magnetic North, while maps and charts always use true North. A bearing measured on a chart won't be the same as a bearing measured by a magnetic compass.

Fortunately, maps and charts provide us with a correction factor called magnetic declination (or sometimes called magnetic variation). The correction factor is simply added (or subtracted) to a bearing to convert the bearing from degrees magnetic to degrees true, or from degrees true to degrees magnetic.

Web site built by Craig Humpleby                                            
Last up dated 05/09/06