“This is a story from long ago, when the great mammoths still roamed our lands. It’s the story of my two brothers and me. When the three of us were young, we were taught that the world is full of magic. The source of this magic is the ever-changing lights that dance across the sky. The shaman woman of our village told us that these lights are the spirits of our ancestors, and that they had the power to make changes in our world. Small things become big. Winter turns to spring. One thing always changes into another. But the greatest change I ever saw was that of my brother. A boy who desperately wanted to be a man…”

– Denahi, Brother Bear

I wouldn’t be surprised if you’ve never seen Brother Bear– it’s one of those early 2000s Disney films that don’t get enough credit, like Treasure Planet and Atlantis.  To catch you up, the film is about an Inuit boy named Kenai, who kills a bear in revenge for the bear killing his brother.  Kenai is then magically transformed into a bear as punishment.  In order to turn back into a human, Kenai must travel to where the lights touch the Earth, all while learning to see the world through another’s eyes.

Kenai bear

In this story, the transformation of Kenai is done by the spirits of the ancestors.  The spirits are represented by the aurora borealis, or northern lights, a natural phenomenon that you can see here on Earth.

The Sun’s outer layer, known as the corona, can reach temperatures of up to 2 million degrees Fahrenheit.  Sometimes, the particles in this layer move so rapidly that they are able to escape the Sun’s gravity in a stream called a solar wind.  These solar winds carry highly charged particles (protons and electrons) at speeds of about 1 million miles per hour to Earth.

solar winds

Once the solar winds reach the Earth, they follow the lines of the Earth’s magnetic field, which directs the charged particles to flow towards the magnetic north and south poles.  These highly charged particles may then interact with elements in the Earth’s atmosphere- namely oxygen and nitrogen.  When the solar wind particles collide with atoms and molecules in the Earth’s atmosphere, energy is transferred, causing electrons in the oxygen or nitrogen in Earth’s atmosphere to become excited and jump to a higher energy.  As they calm down or de-excite back down to a lower energy, they give off photons, small bursts of light.

The color of the light depends on what elements are involved as well as the altitude of the collision.  Each element has a unique emission spectrum, the spectrum of electromagnetic radiation (including visible light) that is emitted in the de-excitation process.

aurora-spektrum

Oxygen can emit bright green and red light, while nitrogen emits red, blue, and violet light.  The exact color seen depends on the altitude of the interactions, as well as the changing abundances of oxygen and nitrogen based on altitude.  For example, oxygen could emit red or green light.  It takes about two minutes for excited oxygen to emit red light, compared to less than a second to emit green light.  A collision of an excited oxygen with another gas molecule can result in an energy transfer with no light emitted.  At very high altitudes above 150 miles, there is a lower concentration of gas molecules, so excited atomic oxygen is less likely to bump into another molecule, allowing it the time to emit red light.  At lower altitudes down to about 90 miles, atomic oxygen is more abundant, allowing more collisions, but preventing red light from being emitted.  This is the range for where oxygen tends to give off green light.  From about 60 to 90 miles in altitude, excited nitrogen may pass energy to oxygen, which then de-excites to give off even more of the green light.

Below about 60 miles in altitude, the amount of atomic oxygen dips, allowing the red, blue, and violet colors from nitrogen to shine through.  While nitrogen de-excitation gives red light, in some cases the nitrogen becomes ionized- that is, it loses an electron.  When the nitrogen gains an electron back, blue light is emitted.  These colors can mix to create other colors such as pink, yellow, or orange.  So while green tends to be the more dominant in visible light in the northern lights, it’s possible to see a range of colors, including the yellow-orange that’s featured prominently in Brother Bear.

Unlike the movie, you can’t really touch the northern lights, as they’re tens or hundreds of miles above the ground.  So sorry, you won’t be able to go transform yourself into an animal in the Brother Bear method.

transformation

Where can you go to see these lights in action?  In general, you’ll probably need to head north.  While the lights have been seen in the southern United States, the lights tend to happen closer to the Arctic.  In Europe, you can catch the lights in the far northern parts of Norway, Sweden, or Finland.  Iceland is another popular choice.  The very northern parts of Russia also fall in prime viewing zones, but it may be difficult to get there.  Northwest Canada and Alaska are more likely to have better shows than northeast Canada due to lower light pollution.  It’s not all location though- you’ll need dark and clear skies, which is why December through April may be better as the skies tend to be less cloudy then.  Even with all this planning, you’ll still need a fair bit of luck- there’s no guaranteeing that the lights will show up on any particular day.

northern lights

You could also head far south to see the southern lights, or aurora australis.  However, these lights tend to show up above Antarctica, which isn’t exactly the easiest place to get to.

Keep calm and science on.

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