The northern and southern lights occur when the solar wind affects our atmosphere, but this can happen on other worlds too

The shimmering northern lights, or aurora borealis, are a natural light show that occurs in a loop around the poles. The southern version is known as aurora australis. Aurorae occur when charged particles emanating from the Sun – the solar wind – crash into the upper atmosphere. A mixture of electrons, protons and helium nuclei, they lose energy as they collide with atmospheric gas molecules. These gas molecules become ionised – some of their electrons are pulled away – and the gases form a glowing plasma. The gas mix governs the colours we see. Red is generated by low concentrations of oxygen at high altitudes. This changes to green as oxygen density increases, with blue generated by nitrogen. Pink, yellow and orange have all been observed, presumably due to the layering of different amounts of red, green and blue. Intriguingly, because our eyes construct our colour perception from red, green and blue-sensing cells, aurorae could form any colour at all depending on the combination of the primary gas colours. Aurorae are clustered around the poles because Earth’s magnetic field dips into the surface. There, particles are repelled from lower latitudes and funnelled into the atmosphere in loops around both poles. But these bands can grow with strong solar storms, occasionally bringing aurora as far south as southern Britain and northern France.