Aurora over Antarctica, ultraviolet satellite image. Australia is at upper left. This is the aurora australis (green ring), the southern lights display. It is caused by interactions between charged particles from the Sun (the solar wind) and gas atoms and molecules about 100 kilometres above the Earth. On reaching Earth, the charged particles are drawn by Earth's magnetic field to the poles, where they collide with gas atoms and molecules, causing them to emit light. This display, on 11 September 2005, was caused by a large solar flare. The aurora image was obtained by NASA's IMAGE satellite, which carried out a five year study of Earth's magnetic field.