"Auroras are created by radiation coming from the sun and hitting Earth's magnetic field. As the solar wind hits the Earth's atmosphere, ionized nitrogen atoms regain and electron and oxygen and nitrogen atoms from excited to ground state. They produce photons during that process, with the oxygen emitting green or brownish-red and the nitrogen producing blue—gaining electrons—or red—going to ground state." (via Gizmodo.com )
Video by Norwegian photographer Terje Sorgjerd.