The natural world is full of all kinds of beauty. But every so often, you come across something so stunning that it doesn’t seem real — and the aurora borealis is one of those things. This phenomenon is commonly known as the Northern Lights, and if you’ve ever seen the curtains, swirls, or streaks of light yourself, it’s something you never forget.
Most people think of the color green when they think of the northern lights. But the truth is that while green is the most commonly seen color in the aurora borealis, the lights come in a spectrum of colors, and that spectrum encompasses hundreds of shades. Here’s a closer look at the many colors of the northern lights and how they form.
Quick Look: How Do Auroras Form?
It’s easy to get so swept up in the beauty of the northern lights that you don’t question how they form. But for centuries, different civilizations came up with their own theories of how the phenomenon came to be. Aristotle called the lights “chasmata” because he believed they were deep chasms in the sky that allowed celestial light to shine in. Cultures who lived far north enough to see the lights sometimes thought they were spirits, omens, or evidence of the activities of the gods.
We didn’t fully understand what caused this otherworldly phenomenon until the 20th century. It starts with “solar wind,” a flood of highly charged particles from the sun. The particles that head toward Earth are caught in its magnetic field, where they get pulled toward the two poles very quickly.
These energized particles speed through the atmosphere until they collide with molecules of air. Each time an atom crashes into an air molecule, the molecule momentarily becomes “excited,” or more energized. Millions of molecules release that excess energy as light, and that forms stunning curtains or swirls of light that unfurl across the sky.
When this phenomenon happens at the North Pole, it’s called “aurora borealis” (“Borealis” means “northern.”). When it happens at the South Pole, it’s called “aurora australis” (“Australis” means “southern.”). However, because very few people live close enough to the South Pole to get a great view of the lights, the northern lights are the ones most frequently seen and photographed.
If you’ve been fortunate enough to see the northern lights in person, you might have (understandably) thought this phenomenon happens very close to the ground. However, the northern lights primarily occur in the thermosphere. As you can see in the diagram below, parts of the thermosphere are hundreds of miles above even the altitude of an airplane.
The Many Colors of the Northern Lights
Now you understand the process of aurora formation. But you might wonder — what causes the different colors? When the electrons in solar wind collide with the gas molecules in the atmosphere, those molecules give off light. The color of the light is primarily determined by the type of air molecule.
1. Green
Green is the most common color seen in the northern lights. You see this color when the charged particles of the solar wind collide with oxygen molecules about 75 to 110 miles above the earth’s surface. Green northern lights tend to be the easiest to see because (1) oxygen is plentiful in Earth’s atmosphere, and (2) this color generally appears closer to the surface of the Earth than any other shade.
2. Red
Red auroras — and specifically those that are as bold as the ones in the picture — are very rare, so you should consider yourself lucky if you see one! Like green auroras, red auroras happen when the charged particles in solar winds collide with oxygen particles. However, you can only see them when those collisions happen at a higher altitude (about 120 miles or higher) above Earth’s surface.
3. Blue
Blue is one of the rarest aurora colors. It happens when both oxygen and nitrogen interact with the charged particles at about the same altitude. Blue auroras are primarily visible when there’s more solar activity than normal — meaning more charged particles are entering the atmosphere.
4. Purple
Sometimes, purple auroras can be seen when other colors mix. However, you might occasionally spot a green aurora with a purple edge or “fringe.” This happens when the air molecules in the atmosphere become extremely excited or energized.
5. Yellow
Yellow auroras are rare, and they often appear in the yellow/pink combination shown above. Like most rare color phenomena, this one usually happens during bursts of solar activity. If the sun emits far more charged particles than normal, there’s more opportunity for those particles to interact with the atmosphere — and that usually means we get to enjoy spectacular color displays.
6. Orange
You don’t see orange northern lights too often. But when they appear, they’re breathtaking! However, this color is more of an illusion than anything — there’s no singular atmospheric molecule that causes an orange aurora. Instead, the lights can appear orange when multiple aurora colors (usually red and green) are present. The photo above is of the southern lights, aurora australis.
7. Pink
Pink auroras can be caused by nitrogen molecules interacting with the charged solar particles at relatively low altitudes (around 60 miles above the Earth’s surface). They’re rare and often appear during “solar storms,” where the sun sends far more super-charged particles — and those particles reach closer to the surface than normal.
What About the Other Colors?
The seven colors listed above could be more accurately described as color categories. For instance, while most people describe green auroras as if they’re a single color, auroras that appear green can range from near-white, frosted shades to bold neons to cool-leaning bluish greens. Much like the colors of the rainbow, the colors of the northern lights fall on a spectrum — and that spectrum includes hundreds of colors.
But did you know that the northern lights are (literally) more colorful than we could imagine? The excited molecules of oxygen and nitrogen also emit ultraviolet light. We can’t see colors on the ultraviolet spectrum, but many birds and reptiles can!
Why the Northern Lights Look More Colorful in Photos
The northern lights are beautiful no matter how you see them. However, if you’ve witnessed them in person and then looked at photos of the same display, you might have noticed that they looked more saturated and colorful in the pictures. This doesn’t mean that the colors are artificially enhanced — it just means that the human eye works a bit differently than a camera.
There are a couple of reasons for this. One is that cameras can use a longer exposure, which essentially means that they can collect more light to use in a photo (while still creating a very sharp image).
Another has to do with the way our eyes work. You probably already know that our eyes have photoreceptor cells that detect light. Cone cells pick up on colors, and rod cells primarily distinguish between light and shadow.
As you might guess, you mostly use your cone cells during the day. However, when you’re in the dark, you mostly rely on your rod cells. That’s why it’s harder to distinguish colors at night. So when you’re standing outside in the dark watching the lights, your rod cells have no trouble picking up on the luminance. They do have trouble picking up on color. That’s why the northern lights may look more washed-out when seen in person than they look in photos.
Take in One of the World’s Natural Wonders
Whether you live close enough to the North Pole to see the northern lights or hope to travel one day to see them, the aurora borealis is a sight you should experience at least once in your lifetime. And once you understand the science behind it, it becomes that much more incredible!
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