A SAR Arc from New Zealand.

What is that unusual red halo surrounding this aurora? It is a Stable Auroral Red (SAR) arc. SAR arc s are rare and have only been acknowledged and studied since 1954. The featured wide-angle photograph , capturing nearly an entire SAR arc surrounding more common green and red aurora, was taken earlier this month from Poolburn , New Zealand , during an especially energetic geomagnetic storm . Why SAR arcs form remains a topic of research , but is likely related to Earth's protective magnetic field , a field created by molten iron flowing deep inside the Earth . This magnetic field usually redirects incoming charged particles from the Sun's wind toward the Earth's poles. However, it also traps a ring of ions closer to the equator, where they can gain energy from the magnetosphere during high solar activity . The energetic electrons in this ion ring can collide with and excite oxygen higher in Earth's ionosphere than typical auroras , causing the oxygen to glow red. Ongoing research has uncovered evidence that a red SAR arc can even transform into a purple and green STEVE .