Recommended Readings Introduction Imagine yourself far out to sea, no land in sight, sailing in a small ship. During the day, you navigate by the sun and at night by the stars. Then it becomes overcast for several long days. This was a discovery which revolutionized the world since it allowed for improved seafaring navigation and exploration. This simple discovery has been developed, over time, into the modern compass.
Compasses work because the earth acts like a giant bar magnet.
Motions in the liquid nickel-iron core of the earth induce a magnetic field with a north and south pole. I said approximately because you'll note in the figure above that the north and south magnetic poles don't exactly align with the earth's axis of rotation which defines the north and south geographic poles. We'll discuss this important fact shortly. Structural geologists use compasses to create geologic maps and measure the orientations of geologic structures. Therefore, in order to do structural geology research in the field, you need to know how a compass works and how to properly use one.