Aurora colors follow the same physics as neon lights. When a charged particle (electron) from the solar wind collides with an atmospheric gas molecule, it excites that molecule to a higher energy state. When the molecule returns to its ground state, it releases the stored energy as a photon of light — and the wavelength (color) of that photon is unique to each gas.
Two factors determine which colors appear: which gas is present and at what altitude. The atmosphere changes composition and density with altitude, so different altitude bands produce different colors.
There is also a third factor: collision frequency. At low altitudes, dense air means excited atoms collide with other molecules before they can emit light. At higher altitudes the air is thin enough that atoms can radiate freely — which is why red aurora only appears high up.
From the most common green to the extremely rare red — what causes each color.
The signature aurora color. Oxygen atoms at altitudes of 100–150 km emit green light at 557.7 nm when electrons excited by solar wind collide with them and release energy. Green dominates because this altitude is where the atmosphere is dense enough for frequent collisions but thin enough to emit visible light efficiently.
Pink and magenta fringe appears at the lower edge of the aurora curtain, where nitrogen molecules are more abundant. Nitrogen emits pink-red light, and when mixed with green oxygen light it creates the pink fringe. Often seen as bright lower borders on intense auroras.
Purple and violet hues come from molecular nitrogen at lower altitudes around 80–95 km. The denser air at this height produces more collisions, giving nitrogen molecules less time to emit longer-wavelength (redder) light before being de-excited. This results in violet and blue-purple emissions.
Blue aurora comes from ionised nitrogen (N₂⁺) at altitudes of 90–110 km. It is rarer because it requires higher energy particles to ionise nitrogen molecules. Blue is often mixed with purple in the lower bands of aurora and may appear near intense activity during strong geomagnetic storms.
Red aurora is rare and spectacular — it appears at very high altitudes (200–300 km) where oxygen atoms are excited but the atmosphere is so thin that collisions are infrequent. Excited oxygen has time to emit red light at 630 nm before being de-excited. Red aurora typically appears at the top of tall curtains during strong (KP 5+) storms.
The human eye is most sensitive to green light in darkness. Weak auroras often appear white or slightly greenish to the naked eye because the intensity is below the color threshold of our cone cells. Cameras with longer exposures can reveal greens, pinks and purples that appear white visually.
The human eye's color vision (cone cells) requires a certain brightness threshold to activate. Weak aurora often appears white or light grey to the naked eye, while a camera set to ISO 1600–3200 with a 5–15 second exposure can reveal vivid greens, pinks and purples.
Strong aurora — KP 5+ — will show full color to the naked eye, often with visible pink and purple at the edges. The green band is usually visible from KP 3 upwards in dark skies.
Read our camera settings guide →