Skylights. (Freeze Frame).

LAST OCTOBER, dazzling multicolored lights lit up Michigan's West Grand Traverse Bay. First signs of an alien invasion? No, they're a celestial spectacle called the aurora borealis, or Northern Lights, which appear most often above the North Pole.

The sky show starts when searing gas particles ejected from the Sun--solar winds--speed toward Earth, explains geophysicist Hans Nielsen at the University of Alaska's Geophysics Institute. The 400-kilometer (250-mile)-per-second winds are pulled toward Earth's polar regions by a powerful magnetic field, an invisible region of forces surrounding the planet. "Solar winds stream around the field like water flowing around a rock in a stream," Nielsen says.

As billions of solar particles collide with air molecules in the outer edge of Earth's atmosphere, the collisions release energy waves that the eye detects as colors, or visible light. Although the Sun churns out solar winds constantly, scientists think its fiery activity peaks toward the end of 11-year-cycles.