Why Colors?
Aurora colors come from which gas is hit and at what altitude. Oxygen at higher altitudes (around 200+ km) can emit red (630 nm); at lower altitudes (around 100 km) it emits green (557.7 nm)—the most common aurora color. Nitrogen produces blue and purple/violet when excited. The mix of altitude, particle energy, and gas density gives the variety of greens, reds, blues, and purples you see. Green is dominant because the green oxygen line is strong and in the visible range where the eye is sensitive. Cosmic Radar shows the daily aurora outlook so you can plan when to look for these colors in the sky.
Sources and further reading
- NOAA – Aurora – Aurora forecast and science
- NASA – What causes aurora – Aurora and magnetosphere
- AuroraWatch UK – When to look and where