Understanding aurora colors; the science behind the display

The Aurora Borealis is a spectacular spectacle, but what’s even more fascinating than its vibrant colors is the science that explains them.

One of the first things that captivated me as a young meteorologist was the northern lights. Witnessing them live as they perform their mystical dance is truly one of nature’s wonders. But have you ever wondered why or how this phenomenon occurs? Let’s dive a bit deeper…

Sun’s energy

Our sun is the main reason for an aurora display. Particles energized by the sun race toward Earth, colliding with our upper atmosphere. Earth’s magnetic field divert this energy towards the north and south poles. As these energized particles enter Earth’s atmosphere, they excite gas atoms and molecules. The colors observed depend on which gas atoms they interact with.

The Earth’s atmosphere is primarily composed of approximately 78 percent nitrogen, 21 percent oxygen and 0.9 percent argon, with trace amounts of other gases like carbon dioxide, methane, and water vapor making up the remaining percentage.

What does each color signify?

Green: The most common color, produced by excited oxygen molecules at altitudes up to 150 miles. Green is the color most frequently seen because our eyes are most sensitive to that wavelength.

Red: Less frequent, this color forms at higher altitudes (above 150 miles) when oxygen emits light in a higher energy state. A lot of reds can be observed during intense solar flares.

Blue: Created by interactions with nitrogen at lower altitudes (below 60 miles), giving a vivid blue hue. Blue aurora’s are more rare than red and green and typically seen around sunset or sunrise.

Purple/Pink: These colors result from both nitrogen and oxygen, often appearing when conditions allow for multiple gas interactions.

Our latest solar cycle, Cycle 25, remains very active, offering more opportunities to view the Aurora Borealis. Happy sky watching!