The Earth’s magnetic poles move. The magnetic North Pole moves in loops of up to 50 miles (80 km) per day. But its actual location, an average of all these loops, is also moving at around 25 miles a year . In the last 150 years, the pole has wandered a total of about 685 miles (1102 kilometers). The magnetic South Pole moves in a similar fashion.
The poles can also switch places. Scientists can study when this has happened by examining rocks on the ocean floor that retain traces of the field, similar to a recording on a magnetic tape. The last time the poles switched was 780,000 years ago, and it’s happened about 400 times in 330 million years. Each reversal takes a thousand years or so to complete, and it takes longer for the shift to take effect at the equator than at the poles. The field has weakened about 10% in the last 150 years. Some scientists think this is a sign of a flip in progress.
The North magnetic pole is at a point where a dipping compass–a compass that allows the needle to move freely in a vertical plane (as opposed to the horizontal needle movements seen in most compasses)–points straight down into the earth. The South magnetic pole is the point where a dipping compass points up. A dipping compass points horizontally on the Earth’s magnetic equator, also called the Earth’s dip equator.
The magnetic poles are quite distant from their geographic counterparts. The North magnetic pole is located to the south in Northern Canada; the geographic South pole is at the center of the Antarctic continent, but the magnetic pole is hundreds of miles away, near the coast. In regions near the magnetic poles, compasses are virtually useless.
Complicating this issue is that these pole positions are not static–for either magnetic or geographic poles. The location of the North geographic pole wanders in a small erratic circle-like path, called the “Chandler wobble.” This motion is less than 6 meters per year on the surface; a worldwide network of very precise global positioning satellite (GPS) receivers is used to determine this wander.