The rotation of the Earth's molten iron core creates electric currents that produce magnetic field lines around the Earth similar to those associated with an ordinary bar magnet. This magnetic field extends several thousand kilometers out from the surface of the Earth. The Sun produces a constant stream of particles which billow out into space and travel at almost 1 million miles per hour. This stream of particles, called the solar wind, varies in intensity with the amount of surface activity on the Sun. The solar wind contains ions from almost every element in the periodic table; however, it consists primarily of protons and electrons. The charged particles of the solar wind