Aurora borealis or northern lights display,over Paris,France,on 13 May 1869,historical artwork. Aurorae,displays of coloured lights in the sky,are rarely seen outside the polar regions. They appear when charged particles of the solar wind are drawn by Earth's magnetic field to the poles,where they collide with gas atoms and molecules,causing them to emit light. The displays can be hundreds of kilometres above the Earth. One reason for auroral displays being seen outside the polar regions is a rise in solar activity. Historical records show that solar activity was increasing in 1869 and peaked in 1870. Artwork by A. Marie,from The Atmosphere (1873) by Camille Flammarion |