Auroral displays are caused by interactions between energetic charged particles from the Sun and the Earth’s atmosphere. Moving at 400-500 kilometres a second, the charged particles of the solar wind are drawn by Earth’s magnetic field to the poles from space, where they collide with gas atoms and molecules, causing them to emit light. Green light is from oxygen atoms, red from nitrogen molecules. The displays can be hundreds of kilometres above the Earth. (Photo by Louise Murray/Science Photo Library Archive)
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