Why do the northern lights change colors?

If you have ever seen a neon sign glowing in the window of your favorite pizzeria, you’ve actually seen a human-made example of how an aurora works. Much like neon signs, an aurora can appear in various colors. The color you see comes down to the type of molecules we are dealing with.

It all begins with the sun. Our home star is constantly emitting a stream of charged particles out into space. Spreading out in all directions, these particles are known as the solar wind.

When the solar wind reaches Earth, particles in the solar wind interact with our planet’s magnetic field. Most are safely deflected away from the planet, but some are captured and pulled in where the field converges near the north and south poles.

An aurora borealis, also known as the northern lights, is seen in the night sky in the early...
An aurora borealis, also known as the northern lights, is seen in the night sky in the early morning hours of Monday, April 24, 2023, near Washtucna, Wash. An intense solar storm has the aurora borealis gracing the skies farther south than usual.(AP Photo/Ted S. Warren)

When this happens, the captured particles become electrically charged and begin to glow. That glow becomes an aurora, which we know best as the Northern Lights (or Southern Lights in the Southern Hemisphere). The lights vary in intensity and shimmer depending on the strength of the solar wind, and can sometimes spread to locations farther away from the poles following solar eruptions.

Green is perhaps the most common and well-known color of the Northern Lights, but the aurora can sometimes appear blue, red, or pink, sometimes even changing from minute to minute. The colors depend on what type of molecule becomes charged by the magnetic field.

Green and red colors come from oxygen molecules, while blue and pink tend to result from nitrogen molecules. A similar process occurs in neon signs, where gas is sealed within a glass tube and glows a certain color when electrically charged. For that reason, you could think of a neon sign or light as an aurora in a bottle!