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Steve4Physics say: True north is the direction directly towards the north pole
Magnetic north is where a magnetic compass points, which is slightly different to true north, because the earth's magnetic field is not exactly lined-up with the earth's axis of rotation.
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Them say: We have arbitrarily agreed that True North is at the "top" of the world....... We picked a spot actually - and then from there we could set the longitude and latitude lines - and the whole world can navigate.
However.......... oddly enough the Magnetic North goes wandering around - and it can go quite a ways from the True North position. So some hapless freighter which is banging along across the Pacific navigating only on his compass and sextant will have to know how far off (today) the magnetic north is from true north. His compass reading won't correspond to True North. Of course nothing is perfect, so the navigator on that freighter will just have to do the best he can.
Now with GPS, you know where you are to the inch, and I don't imagine anybody worries about magnetic north anymore. But on the day some cranky N. Korean blows up our GPS system, we'll all go back to navigating with a compass and sextant.
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