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The Earth's Magnetic Field

Exploring Earth's magnetic field: Intensity and direction

Article Overview

In this article we will cover the following topics:

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Magnetic field marked on Earth's surface

1. Intensity of the Earth's magnetic field

This globe shows the intensity and direction of the Earth's magnetic field at the surface of the Earth. On average, the field strength is about half a gauss; 0.5 gauss or 50 μT. Locally, however, this varies.

For example, the field strength here at K&J Magnetics in Pennsylvania, USA is about twice as strong as in Rio de Janiero, Brazil.

2. Declination of the Earth's magnetic field

Declination is the measure of how magnetic north varies from true north. For example, here at K&J Magnetics in Pennsylvania, USA, the angle between true north (where the top of the globe is, on the spinning axis) and magnetic north (where a compass points) is about 12 degrees.

The globe at below shows the declination of the magnetic field at various locations on the surface of the Earth. In a location where declination is zero, on a bright green line, magnetic north is the same as true north. A compass points to the true north pole.

In a location where declination is a positive number, on a red line, magnetic north is to the right of true north. A compass points to the right of the true north pole.

In a location where declination is a negative number, on a blue line, magnetic north is to the left of true north. A compass points to the left of the true north pole.

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3. Inclination of the Earth's magnetic field

Inclination is the measure of how the direction of the local magnetic field varies from horizontal. At the north pole, the field's direction is straight down. At the south pole, the direction is straight up.

Near the equator, the field direction is about parallel with the surface of the earth. This is shown as the green line where inclination equals zero.

Where inclination is shown as a positive number, with a red line, the magnetic field is pointing down into the ground.

Where inclination is shown as a negative number, with a blue line, the magnetic field is pointing up out of the ground.

Here in Pennsylvania, USA, the direction of the magnetic field is pointed downward at about a 67° angle.

4. Tracing Earth's magnetic field lines north

This globe shows some paths you might follow if you held a magnetic compass and walked north, in the direction it's arrow points. We ignore minor problems, such as walking across water, over mountains, etc.











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