While we’re not sure why auroras have so many different shapes, we do know what causes the different colors. When the Sun’s particles interact with oxygen, the greenish-yellow lights occur. Nitrogen causes the red, blue, and purple lights, and height has something to do with it, too. The lowest lights are the blue ones, while red lights are the highest. And there’s a fascinating variety of myths associated with the lights, from the idea that they’re the spirits of the unborn to harbingers of tragedy or good fishing.