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Our planet has a magnetic field that is approximately aligned with its north–south axis. Humans cannot sense magnetism directly but some animals can, including birds, insects, and even sharks. Migratory birds can fly thousands of miles over open oceans and not lose their way because they sense their direction (north, south, east, or west) from the Earth’s magnetic field. Humans do the same thing with a compass. The north magnetic pole of a compass points toward Earth’s north geographic pole. 
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This should cause you to stop and think a minute! Isn’t the north pole of a magnet attracted to the south pole of another magnet? Why does the north pole of a compass magnet point north on Earth? The answer is that Earth’s north geographic pole is a south magnetic pole. Long ago, people labeled the north magnetic pole of a magnet as the pole that points north! It was more than 1,000 years later when we figured out why the north magnetic pole of a compass needle points north. Although Earth’s magnetic field can be modeled as a large bar magnet, in reality the Earth’s magnetic field is likely created by electric currents within the Earth’s core.
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The direction of magnetic north is actually a few degrees off true north. The deviation between geographic north and magnetic north is called magnetic declination and it is important for navigation. A correction of up to 15º must be made to compass headings to align them to true geographic north. Magnetic declination differs around the world and even varies considerably from state to state within the USA.
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Earth’s magnetic field is slowly changing! A century ago, magnetic north was located at around 70ºN latitude and is now around 83°N latitude. The strength of Earth’s magnetic field has also decreased by about 6% in the past century. In fact, we know from the geological record that Earth’s magnetic field completely reverses itself every million years or so. The last time the Earth’s magnetic poles reversed was around 780,000 years ago. The animated map from the U.S. Geological Survey shows how magnetic declination has changed over the past 400 years.
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If you want to travel directly north, why can’t you just follow your compass needle?
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Compasses point toward the Earth’s magnetic north pole, and the magnetic north pole and the geographic north pole aren’t in the same place. 
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