Aurora
Auroral light is essentially formed from electronically charged oxygen molecules. Green emission predominates at low elevations and red at higher.
Most auroral light is from inspired oxygen atoms. Above 100 km the air is chiefly oxygen atoms and nitrogen particles, whereas the atomic oxygen is disengaged into fragments by solar excessive ultraviolet light. The auroral green light is a unique greatly restricted wavelength of 557.7 nm from very dynamic oxygen particles which is collapsing to a lower, but still excited energy level.