 
The Earth is a giant magnet. Its hot liquid centre core contains iron, and as it moves, it creates an electric curent that causes a magnetic field around the Earth. The Earth has a north and south magnetic pole. These poles aren't quite lined up with the geographic North and South Poles on a map, because the moving inner core's poles are always wandering around.  The north magnetic pole in 2008 was situated near Bathurst Island in northern Canada, about 1600 km from the North Pole. (The south magnetic pole is near the Adélie Coast on the continent of Antarctica, about 2600 km from the South Pole). Both pole positions can wander up to 10 km per year. Because the Earth has a field just like a magnet, it attracts things. In particular, it will attract a small magnetised needle. A needle mounted in a case that lets it move freely will point to the north magnetic pole. We call this needle a compass. Using a compass in the north can give you problems. The needle is actually pointing at the magnetic pole, which is not right at the geographic pole. So your compass may read north, when 'north' is actually in a slightly different direction. Airplane pilots use a compass and map which provide corrections for this 'magnetic variation', to allow them to know which way is true north on the map. These have to be updated every few years as magnetic north wanders away from, or towards, actual north. 
A compass needle on the surface of the Earth will point along the magnetic field lines, towards the north magnetic pole. The needle is actually a tiny magnet, with the north end painted red. This red end is attracted to the 'north magnetic pole'. This means that, magnetically speaking, the north magnetic pole of the Earth is actually a south pole! We call it the 'north' magnetic pole because it's near the top of the Earth, or geographic north, but really it's a magnetic 'south' pole. That's why a compass needle's north end points to it. Earth's magnetic field lines also attract particles from outer space. As particles stream down through the atmosphere towards the magnetic poles, they cause the northern lights. You can also use a special sort of compass to tell you how far you are from the north magnetic pole. If you mount the needle sideways, so that it can dip up and down, you have a dip compass. The closer you are to the north magnetic pole, the more the needle will tilt downwards. Right at the pole, the needle will point straight down. Measuring this 'dip' at the place you're located will tell you how close to the pole you are.    |