COSMIC RAYS
In the early part of this century scientists found evidence for some kind of radiation entering the earth's atmosphere from outer space. Believing the radiation to be electromagnetic in nature, they called it "cosmic rays." Shortly thereafter cosmic rays were shown to consist of subatomic particles rather than electromagnetic waves; but the name stuck, and scientists still refer to them as rays. They should not be confused with very small meteoric particles that also enter the atmosphere.
Cosmic rays consist primarily of protons and helium nuclei (or alpha particles) with some heavier nuclei and a few electrons. They appear to be coming from all directions in space in about equal numbers. The kinetic energies of the cosmic-ray particles cover a very wide range, with the high-energy ones among the most energetic known in nature. There is a lowenergy-that is, a low-velocity-component of cosmic rays that we know to be coming from the sun. Thus scientists divided the cosmic rays into a Galactic cosmic-ray component coming from outside the solar system and a solar cosmic-ray component.
When cosmic-ray particles encounter the magnetosphere, the lowest-energy ones are trapped in the earth's magnetic field, while those with a little larger energies are channeled by the magnetic field to enter the earth's atmosphere at high magnetic latitudes (which is approximately the same as high geographic latitudes). The higher-energy cosmic rays from Galactic space penetrate the magnetosphere almost as if it were not there, striking the nuclei of atmospheric molecules, from which enormous showers of subatomic particles rain down on the surface of the earth. As we go about our daily lives, we are almost continually pierced by these cosmic-ray-shower particles.
The dynamics of these cosmic-ray showers and primary cosmic-ray particles have told us a lot about the earth's magnetic field and the magnetosphere. Charged particles, such as the cosmic-ray particles, are controlled in their motion by magnetic fields and thus are natural probes to reveal the intensity and direction of the magnetic field.
