Short answer
Aurora is light emitted by atoms and molecules in the upper atmosphere when energetic particles from space excite them. Each emitter has its own wavelengths: atomic oxygen gives the common green at 557.7 nm and a deep red at 630.0 nm higher up; molecular nitrogen gives the blues and purples, including an ionised-nitrogen line at 427.8 nm, usually at the lower edge. Faint aurora can look colourless to the eye but colourful to a camera.
Almost every other colour on this site comes from surfaces modifying light that falls on them. Aurora is different: it is the atmosphere itself emitting light. Electrons and protons guided along Earth's magnetic field collide with oxygen and nitrogen high above the ground and raise them to excited states; when they fall back, they emit photons at wavelengths fixed by the energy levels involved. The light is therefore a set of narrow emission lines and bands, much more like a discharge lamp than like daylight, and its colours are the colours of those lines.
The most common auroral colour is a pale green at 557.7 nm from atomic oxygen in an excited state that lives for about a second. The deep red at 630.0 nm comes from a different oxygen state with a lifetime of more than a minute and a half. Lower down, collisions with other molecules knock an excited atom out of its state before it can emit, so a long-lived state can only radiate where the air is very thin. That is why red aurora sits at the top of displays, highest of all, and why all-red aurora — often reported historically as distant fires — is rarer and associated with strong geomagnetic activity.
Molecular nitrogen, and nitrogen ions, emit in the blue and violet and also in the deep red. They emit promptly after excitation, so they can radiate at lower altitudes where oxygen's green is being quenched. The characteristic purple or pinkish fringe along the bottom edge of an active curtain is nitrogen emission; the 427.8 nm line of ionised nitrogen is one of the standard wavelengths auroral researchers image alongside oxygen's green, because both respond to energetic electron precipitation.
Faint aurora is often too dim for the cones, so night vision reports it as a grey or whitish glow; many first-time observers say it looked white. The green line sits close to the peak of both daytime and night-time sensitivity, so it is usually the first colour to become visible as displays brighten, while the deep red at 630 nm is poorly seen by rods at all. Camera sensors integrate light over seconds and have no such threshold, so photographs show greens, reds and purples that the eye did not register — a colour difference that is real, not a processing trick.
| Colour | Wavelength | Emitter | Where in the display |
|---|---|---|---|
| Green | 557.7 nm | Atomic oxygen | Most common; the main body of curtains |
| Red | 630.0 nm | Atomic oxygen (long-lived state) | Highest altitudes, tops of rays |
| Blue-violet | 427.8 nm | Ionised molecular nitrogen | Lower levels; with energetic precipitation |
| Purple, pink | Bands in blue and red | Molecular nitrogen | Lower border of active curtains |
Each statement is labelled by kind — established fact, a standard’s requirement, observed market data, a convention, or Colourwise’s own interpretation or analysis — with the strength of the evidence behind it.
FactStrong evidence
The most common auroral colour is a pale green at 557.7 nm from atomic oxygen; a deep red comes from a longer-lived excited state of atomic oxygen and is found only at high altitudes; purple comes from molecular nitrogen at lower altitudes.
Source: Aurora Tutorial
FactStrong evidence
The red oxygen line is at 630.0 nm, and the 427.8 nm band of ionised molecular nitrogen is one of the main auroral emissions observed with the 557.7 nm green line.
Source: Observations of ion upflow and 630.0 nm emission during pulsating aurora; Causes of Color (WebExhibits); The vivid lights: what causes the colour of the aurora?
FactStrong evidence
Faint aurora is often reported as white because night vision detects brightness without distinguishing colour, while digital cameras can record auroral colour when it is too dim for the eye.
Source: Aurora Tutorial
FactStrong evidence
The green oxygen state has a lifetime of about one second and the red state more than 150 seconds, which confines red emission to the thin upper atmosphere where collisions are rare.
Source: Aurora Tutorial
Reviewed 29 September 2026. Colourwise summarises its sources in its own words and does not reproduce standards text or proprietary colour data. Spotted an error? Tell us.