Magnetic Field and Cosmic Rays
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.
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
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
Illinois Central College
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Update: June 2012