| Term: | Aurorae |
| Definition: |
A phenomenon consisting of luminous colorful arcs, rays, and streamers that appear in a planet's upper atmosphere during the night with the greatest frequency in the northern and southern polar magnetic zones. This non-thermal radiation is caused by the emission of light from atoms excited by electrons accelerated along the planet's magnetic field lines at the magnetic poles. Fluorescent emission from atomic oxygen at 5557 Å results in a greenish glow, and there is a weaker effect from the red line at 6300 Å. Blue and purple colors are emitted by atomic and molecular nitrogen. |