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Aurora borealis in the night sky over Iceland, with a lake in the foreground. The aurora borealis is a coloured light display (the northern lights) that is visible in the night sky, usually only at high latitudes. It occurs when charged and energetic particles from the Sun (the solar wind) are drawn by Earth's magnetic field to the polar regions. Hundreds of kilometres up, they collide with gas molecules and atoms, causing them to emit light. Photographed in Thingvellir National Park, Iceland. (KEYSTONE/SCIENCE PHOTO LIBRARY/JUAN CARLOS CASADO (starryearth.com) / SCIENCE PHOTO LIBRARY)