From science and technology to engineering and math, Magnetic North is a perfect STEM subject, starting with its origins. Earth’s rotation slowly swirls a molten soup of metals deep within the planet, creating powerful magnetic fields that exert their greatest influence from two areas on the globe’s surface: the magnetic poles.
The ebb and flow of Earth’s magnetism cause the poles to drift at a rate of 10 miles or more each year. Magnetic North is currently in the Arctic Sea about 500 kilometers from the true North Pole and moving in a northwesterly direction. Magnetic South is off the coast of Antarctica.
You can detect Earth’s magnetic fields by stroking a steel needle with a magnet and then placing the needle on a small wood chip floating in a bowl of water. The needle will stabilize with one end pulled toward Magnetic North and the other toward Magnetic South.
Similar experiments a thousand years ago led to the development of the compass, one of humankind’s greatest inventions. With it, explorers could venture into the unknown and then find their way home again.
Many early travelers believed compass needles were drawn toward a magnetic mountain in the far north. Gradually, scientists came to understand the existence of magnetic fields. In 1831, British navigator James Clark Ross was the first to reach the Magnetic North Pole, determined when his ship’s compass needles were drawn straight down.
Attracted by magnetic fields rather than True North, the needle of every magnetic compass speaks the language of Magnetic North.
On the other hand, most maps are drawn with the geographic North Pole as their main reference. Extend the side margins of a topography map far enough and you’ll find yourself at the North Pole. In general, maps can be said to speak the language of True North.
A diagram in the margin of most topography maps indicates the difference between a map line extending to True North and another drawn toward Magnetic North. That difference — the map’s declination — is noted in degrees.
In portions of Mississippi, Arkansas, Missouri, Iowa and Minnesota, a compass needle pointing toward Magnetic North will also appear to be aimed at True North. Lines drawn to Magnetic North and to True North will appear to be as one. This agonic line takes its name from an ancient Greek mathematical term meaning “without angle.”
Go east or west of the agonic line, and the lines spread apart as the angle of declination increases. By the time you reach Washington in the west or Maine in the east, declination can be 20 degrees or more. That can lead to dramatic errors in navigation when a map and compass are used together.
[Don’t Be] Lost in Translation
The easiest remedy is to teach your compass to speak the language of True North. Some adjustable compasses let you account for declination by using a tiny screwdriver to reposition the floor of the compass housing.
For non-adjustable compasses, red fingernail polish will do the trick. Check the declination diagram in the map margin and note the number of degrees. If the Magnetic North arrow is to the right of the True North arrow, put a dot of polish that many degrees to the right of N on the compass rim. If it is to the left, put the dot on the left side of the N.
Rather than lining it up inside the needle outline on the floor of the housing as you take bearings, point the north end of the needle at the dot of polish. Your compass will be speaking the language of True North, the same as your map, and you will be all set to go.
When your adventures take you to a different area, wipe off the first dot with fingernail polish remover and apply a fresh mark on the rim at the correct number of degrees to match the new declination.
Magnetic North is not an issue for Global Positioning System receivers, cellphone map programs or other electronic navigational aids that rely on satellites rather than magnetic fields for points of reference.
Even so, the attraction of the Magnetic North Pole is at the heart of developing strong route-finding skills that won’t go down when batteries run dry. And that is worthy of celebration any time you need to find your way.
For more on the Magnetic North Pole, see the current editions of the BSA Fieldbook and Orienteering merit badge pamphlet.