Magnetic Poles Galore

A great way to understand the main field of the Earth is to examine the magnetic pole positions that are marked on global maps. If we don't stop at the first chart viewing, but instead compare a few poles that are available in the literature, we see a problem immediately. There are many magnetic poles used by different groups. For example, scientists often refer to a pair of locations they call the "Geomagnetic Poles" and use the geomagnetic latitude and longitude coordinates about these poles to organize their upper atmosphere and space data (Figure 3.3).

Geomagnetic Latitude
FIGURE 3.3 ► Curves of geomagnetic latitude and longitude lines converge at the Geomagnetic North Pole in northwest Greenland.

Most commercial world maps (e.g., those by National Geographic, Rand McNally, and Hammond) indicate two unique "Magnetic Pole" positions. One is in the Queen Elizabeth Islands region of northern Canada (Figure 3.4) and the other is just off the Antarctic continent toward the Australian island state of Tasmania. The cartographers and news media tell us that these poles are "the locations toward which all world compasses point," a false explanation that is reminiscent of the "magnetic mountain" model of Columbus's time.

For many years following a famous 1831 discovery of the "Magnetic Pole" in northern Canada by James Clark Ross, expensive polar magnetic expeditions have set out for the sole purpose of establishing these distant spots where the Earth's magnetic field points directly into the ground. The basis for this effect has its roots in Gilbert's 1600 textbook (Figure 1.5) showing the Earth's field as an Earth-centered dipole magnet. It is now known that in reality there are five candidates for this important "Magnetic Pole" designation (Figure 3.5). To further confuse this situation, it appears that the cartographers' vertical-field locations are, most certainly, not the important

FIGURE 3.4 ► A map of northern Canada with a dubious "North Magnetic Pole" marked in the Queen Elizabeth Islands. Figure adapted from Citation World Atlas, Hammond Inc.

pole locations "to which all world compasses point." So that we can better understand this universal misconception, let's tour along with the scientists who measure the main field of the Earth.

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