Why auroras glow green, red and purple
Energetic particles make oxygen and nitrogen in the upper atmosphere emit light. The gas, its energy state and altitude help determine the colours, while a camera can reveal light our eyes miss.
The green ribbons of an aurora come from gases in Earth’s own upper atmosphere. Energetic particles arriving from space transfer energy to those gases, which release light. Oxygen is responsible for familiar green and red emissions; nitrogen contributes blue and pink, and overlapping light can appear purple.
How a collision becomes light
The process starts well beyond the glowing curtain. The solar wind interacts with Earth’s magnetic environment, transferring energy into the region called the magnetosphere. Energy released there can accelerate particles toward the atmosphere. This is more involved than sunlight simply reflecting from the sky.
NOAA explains that visible auroras are mainly produced by electrons. Guided along Earth’s magnetic field, they collide with oxygen and nitrogen atoms and molecules, raising them into higher energy states. As the gases return to lower states, they emit light. Each visible curtain combines the light from enormous numbers of such interactions.
The magnetic field also helps organise the display geographically. Auroras commonly form in two oval-shaped regions around the magnetic poles. During major geomagnetic storms those ovals expand toward lower latitudes, making the lights visible farther from the polar regions. That explains where a display may spread; the atmospheric gases explain its colours.
Why oxygen can glow both green and red
A gas does not have just one possible colour. Different changes in its energy state can release different colours of light. NASA’s aurora guide places common green oxygen emission roughly 100–200 kilometres above the surface, with red oxygen emission above about 200 kilometres.
Nitrogen adds blue and pink light. The result depends on the gas’s state, the particles interacting with it and where the interaction occurs. Light from different emissions can overlap in our view, producing mixtures that look purple, pink or white. These are broad relationships, rather than sharply separated coloured floors in the sky.
Colour therefore provides clues about the emitting gas and conditions, but a photograph alone does not give a precise altitude for every bright patch. The comparison illustrates typical associations; it does not measure the height of the ribbons in the space-station photograph.
Why photographs can look more colourful
A camera and an observer’s eyes do not record a dim display in the same way. NASA’s photography guide notes that sensitive digital cameras can capture auroras that are not visible to the naked eye. A vivid image is therefore not a guarantee that someone standing below saw equally vivid colours.
The photograph here is an identified example, rather than a forecast: an Expedition 75 crew member captured it above Kyrgyzstan on September 7, 2026. NASA published the processed view on September 16, explaining its contrast enhancement and removal of lens artifacts. Those processing details and the observation date remain separate from the underlying explanation of how auroral light is made.
Join the conversation