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Northern lights: What causes the colors that we see — and don’t see?

(NEXSTAR) — Amid a massive solar storm, Americans as far south as Hawaii, Florida, and Texas have had the chance to see the northern lights. For some, it’s the first time in nearly two decades that conditions aligned to bring the aurora to their night skies.

If you saw the northern lights — either with your own eyes or with the help of your phone — you may have noticed an array of colors. But what causes the different shades of greens, reds, blues, and purples? It’s all about what’s hitting our atmosphere, and what it’s interacting with.

Northern lights are sparked by coronal mass ejections, or explosions of plasma and magnetic material shooting out of the sun, colliding with Earth’s magnetic field. As those ejections, known as CMEs, smack into our magnetic field, currents send particles flowing to the North and South Poles.

Those particles will ultimately interact with the gases in our atmosphere: oxygen and nitrogen. The excess energy created by those interactions, according to NASA, will cause a burst of light which we see as the aurora.

What color we experience depends on which gases are involved and where it happens.

Green northern lights, the most common, occur when particles interact with oxygen between 75 and 110 miles in altitude. If oxygen and nitrogen are “excited by the incoming particles” at the same altitude, we can see blue aurora, NASA explains.

Slight lower, 60 miles and below, an interaction with nitrogen will cause pink northern lights. Above 120 miles, interactions with oxygen spark red aurora.

Like mixing paint, when these colors blend, you may see purples, whites, and other shades of pink.

Our eyes aren’t always able to see the shimmering northern lights, even though we know they’re out there. However, your phone’s camera (as long as it’s newer) may capture it because they are often more sensitive than our eyes, Michael Bettwy, operations chief of NOAA’s Space Weather Prediction Center, said last week.

“You may not be able to see it with your naked eye, but if you have a clear night with not that many clouds, and you put your phone to the sky, you may actually get an image or two,” Bettwy said.

Visit Iceland (where northern lights are visible more frequently) recommends adjusting your phone’s settings to get the best shots. Look for something like “night mode” or another way to lengthen the camera’s exposure to help capture more light. Using a tripod can also help keep your hands steady.

Alix Martichoux contributed to this report.

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