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Name: Andie
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Grade: other
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Date: 8/17/2005

How does the magnetic field around the earth protect us from cosmic ray bombardment?

Cosmic rays are charged nuclear fragments, usually protons, traveling at almost the speed of light. The Earth's magnetic field will deflect the particles somewhat, but their speed is so high the deflection is not so large as to "stop" the particle. Cosmic rays can be detected at the Earth's surface. The magnetic field of the Earth deflects and captures particles -- electrons, protons, helium nucleii (alpha particles) -- emitted by the Sun (called solar winds). However, the speed of these fragments is much slower than the speed of cosmic rays.

Vince Calder


Cosmic rays are composed of many particles. Most of the particles are charged (some positive, some negative). The charged particles are the ones that will do the most damage.

When a charged particle moves ACROSS a magnetic field (i.e. velocity not aligned with the field), the magnetic field causes the particle to turn. Although positive particles turn one way and negative particles turn the other, the Earth's magnetic field turns all of them away from us. Uncharged particles, such as neutrinos, just pass through us without much effect. Neutrons can do damage, but they have another safety factor. By the time neutrons reach the Earth, most have changed into a proton, an electron and an antineutrino. The proton and electron are turned. The antineutrino just passes through.

One dangerous particle that is not turned by the magnetic field is light. High energy light (ultraviolet, x-rays, gamma rays) could hurt us. The atmosphere protects us from these.

Dr. Ken Mellendorf
Physics Instructor
Illinois Central College

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