What are Aurorae?
Aurorae are a luminous glow of the upper atmosphere caused by energetic particles descending from the Earth’s magnetosphere or coming directly from the Sun. These energetic particles are mostly electrons, but protons can also be involved, and their energetic rain into the atmosphere is greatest during magnetic storms. As the particles descend, they collide with molecules in the atmosphere, causing an excitation of the oxygen and nitrogen molecular electrons. The molecules can return to their original, unexcited state by emitting a bit of light, a photon. This light, a photograph of which appears in the banner of this website, is the aurora that we see. Since electrically-charged particles tend to follow magnetic-field lines, and since magnetic-field lines are oriented in and out of the Earth and its atmosphere, near the magnetic poles, aurorae tend to be seen at high latitudes.
