aurora

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aurora Illumination of the sky, sometimes in brilliant colours, as a result of high-speed solar particles entering the ionosphere (at a height of 100–130 km) and releasing electrons from air molecules by excitation. The re-establishment of molecules leads to the emission of light, especially red- and green-coloured light, e.g. in arcs or bands over large areas. The effect is called ‘aurora borealis’ or ‘northern lights’ in the northern hemisphere and ‘aurora australis’ or ‘southern lights’ in the southern hemisphere. Such atmospheric disturbances occur in relation to disturbances on the Sun in the course of the sunspot cycle.

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