The magnetosphere, or the magnetic field of the Earth, is not something most people will think about, but it is responsible for so much, including life as we know it. Pelted each moment by deadly radiation from the Sun, the magnetosphere blocks these deadly rays from reaching the surface. Most of the planets in the Solar System have their own magnetosphere, acting in a similar way to our own.
Zone in on the basic facts on the magnetosphere:

1. The magnetosphere is the magnetic field surrounding Earth and protects it from deadly cosmic rays that would otherwise make life as we know it impossible.

2. The magnetosphere is caused by the rotation of the Earth’s core, which is mostly iron and other, heavier, metals.

3. The Earth’s magnetic field was studied as early as 1600 by English astronomer and physician William Gilbert (1544-1603), and the first satellite to study the magnetosphere was NASA’s Explorer 1 probe in 1958.

4. The aurorae seen at extreme northern and southern latitudes (also called the Aurora Borealis and the Aurora Australis, respectively) are caused by particles from the Sun interacting with the poles of the magnetosphere.

5. The magnetosphere allows compasses to work on Earth, as magnetic North is part of the planet’s magnetic field.

6. On the side facing the Sun, the magnetosphere extends outward about 40,000 miles (or about 64,300 kilometers) but extends outward almost 4 million miles (6.4 million kilometers) facing away from the Sun.

7. NASA astronomers suggest that the magnetotail, the end of the magnetosphere facing away from the Sun, may cause small dust disturbances on the Moon from time to time as it passes through the Earth’s magnetic field.

8. Since the solar wind shapes the magnetosphere, the magnetotail always points away from the Sun.

9. Some of the charged particles from the Sun are trapped in an area of the magnetosphere called the Van Allen Radiation Belts (after American astrophysicist James Van Allen (1914-2006)), extending about 600 miles to 37,000 miles (or 965 kilometers to 59,545 kilometers) above the surface of the Earth, but astronauts face few radiation hazards from the belts because of protective shielding and careful orbits.

— Dr. Bridges is a professor of history and geography living in Arkansas. He can be contacted at