Protons and electrons stream away from the sun at speeds of up to 3 million miles per hour, creating what's known as solar wind. As this particle-filled wind hits the magnetic field surrounding earth, it's drawn toward the magnetic poles. Along the way, it collides with and energizes atoms (mostly oxygen and nitrogen) in the earth's upper atmosphere. When these energized atoms return to their normal state, they release energy in the form of colored light-most commonly pink, red, or ghostly green. Exactly which colors you see depends on several factors, such as altitude, the amount of energy being released, and gases encountered in the atmosphere. But generally, the colors fall into one of five basic auroral types: green with red along the top; green with red along the bottom edge; all green; all red; and blue-purple sunlit auroras.