Aurora are natural coloured light displays in the sky, usually observed at night, particularly in the polar zone. They typically occured in the ionosphere. Some scientists called them "polar aurora". Aurorae are produced by the collision of charged particles from Earth's magnetosphere, mostly electron but also proton and heavier particles. The auroras is a common occurance in the Poles. It is occasionally in temperate latitudes, when a strong magnetic storm temporarily expand the auroral oval. The ultimate energy source of the aurora is the solar wind flowing past the Earth. Images of aurora are significantly more common today due to the rise of use of digital cameras that have high enough sensivities.