Ladies and Gentlemen
Welcome to the greatest free show on earth. Take a look at this (sorry about the music..) These spectacular images, named after the Roman goddess of dawn are called auroras, both surrounding the north magnetic pole (aurora borealis) and south magnetic pole (aurora australis). They occur when fast moving electrons from the solar wind interact with elements in the earth’s atmosphere. Solar winds, plasmas of charged particles, stream away from the sun at speeds of about 1 million miles per hour. When they reach the earth, some 40 hours after leaving the sun, they follow the lines of magnetic force generated by the earth’s core and flow through the magnetosphere, a teardrop-shaped area of highly charged electric and magnetic fields which protects us from the wost ravages of the solar wind.
As the electrons enter the earth’s upper atmosphere, they encounter atoms of oxygen and nitrogen at altitudes from 30 to 300 km above the earth’s surface. The color of the aurora depends on which atom is struck, the exact excitation event and the altitude of the meeting. The magnetic and electric forces interact with one another in constantly shifting combinations. These shifts and flows can be seen as the auroras “dance,” moving along with the atmospheric currents that can reach 20,000,000 A at 50,000 V. By comparison, the circuit breakers in your home will disengage when current flow exceeds 15-30 amperes at 240 volts.
This video from howstuffworks is good