Making an Aurora The aurora takes its name from the Roman goddess of dawn, but its cause has nothing to do with the Sun's light (early explanations even suggested that auroras were simply the reflections of light off of ice crystals in the atmosphere). The light from auroras is actually similar to light produced by a neon sign – some gases become excited and glow when electricity passes through them. The solar wind sometimes causes disturbances in Earth’s magnetosphere. Auroras occur when high-energy electrons from the magnetosphere are guided by Earth's magnetic field towards the polar regions and our atmosphere. There, they collide with oxygen and nitrogen, atoms, electrically exciting these gases so that they emit light, much like the glow of a fluorescent lamp, a neon sign, and even your TV. Auroras Come in Different Colors Auroras that are most often seen occur about 100-160 km (60-100 miles) above Earth's surface. Different atmospheric gases emit different colors of light when excited (i.e. they have a unique EM spectrum). The particular color you see depends on the type of gas and how much energy the electrons have when they strike the ionosphere. Yellow-green and red auroras are caused by excited oxygen. Excited nitrogen is responsible for blue and purplish auroras as well as some red ones. The figure on the left compares light emitted from the Sun (continuous spectrum) to one from an aurora (discrete spectrum). Notice how different they are.