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True North vs. Magnetic North

Before we start working with the compass we need to discuss how True North and Magnetic North differ.  True North is the geographic north that points to the north pole.  This geographic point is located directly below the North Star - Polaris.  The geographic north pole is the location of the axis on which the Earth revolves about.

Magnetic North on the other hand are not necessarily aligned with True North or the Earth's rotation axis.  The Earth's magnetic fields are slightly off.  In fact the magnetic fields point in a slightly different direction depending on your location on Earth. Furthermore, the direction of the magnetic fields change a little bit over time. ( kind of confusing is it not?)

The picture below is an illustration of the North Magnetic Pole and the True North or Geographic North.

Magnetic Declination

The angle difference (measured in degrees) between True North and Magnetic North is called Declination. Here in the United States, the magnetic declination changes depending on where you are standing in the US.  If you are in the East Coast, the magnetic declination points westerly to the left.  If you are in the West Coast, the magnetic declination points approximately 20 deg. easterly to the right.

So if you are standing on Washington State, your compass will point to magnetic north which is 20 degrees east of true north.  If you are navigating over relative short distances, this difference may not be an issue.  However, if you require a higher level of accuracy or if you are traveling over large distances, then you must be able to account for declination and make the necessary adjustments.

Every topo map has a legend at the bottom.  There you will find two arrows; one pointing to True North (N, TN or ★)  and the other pointing to Magnetic North (MN) as shown on the image on the right.  If you were to follow the True North arrow, you will go straight up.  However if you were to follow the magnetic arrow, you will move slightly at an angle towards the right.  The further away you move along magnetic arrow, you would end up further away from true north.

So to sum it up, your map is aligned to True North, and your compass points to Magnetic North.  So how do you use both tools to navigate if they point to two different directions?  Well that's the topic of the next article:  How to align your map with your surroundings using a compass.