Does a Compass always point North?

     Scouts and sailors can tell you how important compasses are. Day or night, rain or shine, a compass will always show you where north is, or will it?  Does a compass always point north? What does it do at the north or south pole?  I was recently asked the following question on this subject.

     "Recently some sailors sailed in the South Pole region of the Earth. I would like to know what reading their compass showed as they sailed South to get as close to the pole as possible. What would happen if they left their ship and hiked overland to the magnetic south pole?"

     Hold a compass in your hand and it will point to the Earth's north pole. Why? Because the Earth is like one giant magnet and the compass points to the magnetic north pole. In fact, even if you go south of the equator and quite close to the south pole, the compass will still point to the north magnetic pole. With only two exceptions, it will always behave that way.  But first, you might wonder why the Earth behaves like a magnet at all.

     To best understand Earth's magnetic field, picture a bar magnet and a bunch of iron filings dumped around it. The filings form lines running from the north pole of the magnet to the south pole of the magnet. We call these lines magnetic field lines. The compass is acting somewhat like the iron filings and is pointing towards the north pole. The actual cause of the magnetism has to do with the interior of the Earth.

     We know that at the center of the Earth lies a molten metallic iron rich core. The outer portion of this core is molten. We also believe that this core is spinning. Our knowledge of the details of exactly what causes the magnetic field is sketchy but it is believed that the metals in the core have many loosely bound electrons and that these particles can conduct electricity. It is this mass  of moving electrons which produces the magnetic field.

     So now we know what causes the magnetism that attracts the compass. The sailors mentioned above also saw their compass pointing to magnetic north even though they were as far south as Antarctica. And we know that the compass nearly always points to magnetic north. So what are those two exceptions? If you were to take a compass and stand just over either the north or the south magnetic pole, you would see the compass spin freely. From the south pole, every direction is north and from the north pole, there is no north. But there is still a way you could know where you were!

     The kind of compass we usually think of is a standard compass -- held horizontally -- its needle is only free to move around to the left or the right. A different sort of compass, called a "dip compass," has a needle that moves in the vertical direction, rather than in the horizontal. From magnetic south, its needle would point straight up into the sky -- because at the south magnetic pole, the magnetic field emerges straight up out of the ground. At the north pole, the opposite end would point up.

Copyright © 2001 Kathy A. Miles and Charles F. Peters II