Why Is the Aurora Green? A Guide to Aurora Colors
Everyone pictures a curtain of green when they think of the Northern Lights, and most of the time that's exactly right. But the Aurora can also glow red, purple, pink, and blue. Every one of those colors comes down to the same two gases and a difference in altitude of a few hundred kilometres. Here's what actually produces each color, and why your camera often sees shades your eyes can't.
It all comes down to two gases and altitude
The Aurora happens when charged particles from the solar wind funnel down Earth's magnetic field lines and slam into the upper atmosphere. Those collisions excite electrons in oxygen and nitrogen atoms, and when the electrons drop back down they release the extra energy as light. Which color you get depends on which gas gets struck and how high up the collision happens.
Think of the atmosphere as layered, with different gases dominating at different heights. That's the whole secret to Aurora color: it's really a map of altitude.
Green: the signature color
The classic Aurora green comes from oxygen atoms around 100–300 km up, emitting light at a wavelength of 557.7 nanometres. It's by far the most common Aurora color, for two reasons: oxygen at that altitude is abundant, and it happens to be the easiest excited state to trigger.
Red: the rare, high-altitude glow
Higher up (roughly 300 to 400+ km, where the atmosphere is far thinner), oxygen can also emit a deep red light at 630 nanometres. This transition is much slower (it takes almost two minutes for the atom to release the photon), so it only survives at altitudes where collisions with other molecules are rare enough not to interrupt it first.
Red Aurora tends to show up during the strongest geomagnetic storms, when particles penetrate to unusually high energies and altitudes. It's the color behind some of the most famous Aurora sightings in history: the 1859 Carrington Event reportedly turned skies blood-red as far south as the Caribbean, and the May 2024 G5 storm produced a similar red glow visible from Mexico and Florida.
Blue and purple: nitrogen's contribution
Lower down, below about 100 km, nitrogen molecules take over and can glow blue or purple. This requires the most energetic, fastest-moving particles, since they need to punch deeper into the thicker lower atmosphere before colliding. Blue and purple typically appear as a fringe along the bottom edge of a bright curtain during an intense, fast-moving substorm, rarely as the dominant color on their own.
Purple and magenta hues you sometimes see in Aurora photos are usually a blend: nitrogen blue at the base mixing with the much more common green above it, sometimes with a touch of high-altitude red at the very top of a tall curtain.
Cheat sheet: color, gas, altitude
| Color | Gas | Altitude | How common |
|---|---|---|---|
| Green | Oxygen | ~100–300 km | Very common, the default |
| Red | Oxygen | ~300–400+ km | Rare, strong storms only |
| Blue / purple | Nitrogen | ~60–100 km | Rare, fast substorms only |
| Pink / magenta | Blend | Mixed altitudes | Occasional, at curtain edges |
Why your camera sees more colors than your eyes
This is the single biggest source of both Aurora disappointment and Aurora delight, often on the same night. In low light, the human eye relies on rod cells, which are far more sensitive to brightness than to color, so a faint Aurora often looks like a pale grey or washed-out green haze to the naked eye, even when it's genuinely active. A camera sensor doesn't have that limitation: given a multi-second exposure, it accumulates light and renders the true, saturated color the whole time.
Rare and exotic colors: STEVE
Occasionally you'll see a narrow, glowing mauve-to-pink ribbon that isn't classic Aurora at all: it's called STEVE (Strong Thermal Emission Velocity Enhancement). STEVE is produced by a different mechanism (a fast-moving ribbon of hot, drifting gas in the upper atmosphere rather than the usual particle-precipitation process), and it's often accompanied by a picket-fence pattern of green vertical stripes beneath it. It was only formally studied in the last decade, discovered in large part thanks to citizen Aurora photographers.
Check tonight's forecast to see what color you might catch→So next time someone asks why the Aurora is green, you've got the real answer: oxygen, around 100–300 km up, the easiest color for the atmosphere to produce. Everything rarer (red, blue, purple, STEVE) is a sign you caught something special.