This is a guest post from Jeff.
The northern lights, or aurora borealis, have dazzled and puzzled humanity for millennia. More recently, science has provided answers for many of our questions about what causes this incredible display of light. Thousands of years ago, however, ancient civilizations didn’t have the insights we do now, and created their own stories to explain the origins of the northern lights.
The Cree, one of the largest populations of Native Americans in North America, referred to the northern lights as the “Dance of the Spirits”. They believed that the spirits of their loved ones and relatives watched over them and danced for them in the sky.
The Inuit of Alaska believed that the northern lights were the spirits of the animals that they hunted, such as salmon, deer, beluga whales and seals. The Menominee Indians of Wisconsin believed that the lights were a sign of “manabai’wok” – giants who embodied the spirits of great hunters and fishermen.
In medieval times, the northern lights were thought by some in Europe to be a harbinger of doom. Central Europe is at a lower altitude than Northern American and Nordic countries, so the northern lights occur there only very infrequently and the lights are usually red. Fearful central Europeans associated red with war, and assumed that the lights meant war was on the horizon. Further south, in France and Italy – which are at an even lower altitude and where the lights occur less frequently – the aurora were believed to be a signal of coming plague, illness or death.
What We Know
Today we know a little more. The northern lights are caused by the collision of energetic charged particles with atoms in the thermosphere, which is a higher point in our hemisphere. The charged particles that collide with gaseous elements in our atmosphere generate the magnificent coloured light we see.
When they’re electrically charged, neon bulbs get their colour depending on the type of gas that fills them. For example, helium creates orange to white light, argon creates lavender light, krypton causes green light, and so on. Similarly, the colour of the northern lights depends on which gases collide with solar particles, which are carried to Earth by solar winds from the upper atmosphere of the sun.
Accordingly, the colours we see in the northern lights depend on the height at which the collisions occurs. Very high up in the thermosphere, around 300 kilometres from the Earth’s surface, oxygen is the most common gas. Collisions with oxygen create a rare orange aurora. Collisions with oxygen at lower altitudes, between 100 and 300 kilometres, create the more common range of yellow and green light. At 100 km from the Earth’s surface, there are higher levels of nitrogen. Collisions at this level are far more rare and create the red light that so terrified medieval Europeans.