ABSTRACT
Charged particles from the sun, usually protons, encounter the earth’s magnetic field, spiral down toward the negatively charged earth, and meet the atmosphere above the magnetic north and south poles (Figure 6.1). The charged particles from the sun are moving at high speed and begin to collide with molecules of oxygen, nitrogen, and other gases in the upper atmosphere. These high-energy collisions cause electrons in the gas molecules to be excited into higher energy orbitals to form excited atoms or ions (Figure 6.2). Additionally, nitrogen and oxygen ions are formed if an electron is ejected from a molecule by the energy of collision. During this process, the remaining electrons in the ions may also be excited. Other gases are present in the atmosphere, such as carbon dioxide, and argon, and these also form excited molecules and ions. When the electrons in the excited atoms or ions return to their original (ground) state, light is emitted. The light can be green, red, or other colors, depending on which molecules have been excited (Figure 6.3).
