Auroras: The Northern and Southern Lights
Auroras aren't visible while the sun is shining, but our stormy star is the source of these nighttime shows. The sun generates a constant stream of charged particles, or plasma, that's ejected in all directions into space. When this so-called solar wind slams into the invisible magnetic field surrounding Earth, it produces currents of charged particles, mostly electrons, which flow toward the Poles. In the upper atmosphere, solar particles collide with gas atoms and "excite" them with extra energy, which then gets released as light.
An aurora's brilliant colors are determined by the compositions and densities of atmospheric gases—mostly oxygen and nitrogen—found at different altitudes. Reds are the highest of the auroral colors, appearing above 150 miles (240 kilometers). It takes