How it forms
The Sun constantly streams out charged particles as the solar wind, and flares or coronal mass ejections (CMEs) release far more. Earth's magnetic field deflects most of them, but as the field and the solar wind interact, energy builds up and particles are funnelled along magnetic field lines into the upper atmosphere around the poles. There they excite oxygen and nitrogen atoms, which give off light of particular colours as they return to their normal state. That is why auroras are seen most often in a ring-shaped auroral oval around each magnetic pole, at roughly 65–70 degrees magnetic latitude. The name aurora borealis is traditionally credited to Galileo in 1619, combining Aurora, the Roman goddess of dawn, and Boreas, god of the north wind.
Why the colours differ
An aurora's colour depends on which atoms emit light and at what height. The common green glow is oxygen emitting at 557.7 nm between about 100 and 250 km; higher up, where the air is very thin, oxygen gives off red light at 630 nm. Nitrogen adds purple or pink fringes along the lower edge.
| Colour | Source | Approx. height |
|---|---|---|
| Green | Atomic oxygen, 557.7 nm | About 100–250 km |
| Red | Atomic oxygen, 630.0 nm | Above about 200 km |
| Blue/purple | Ionised molecular nitrogen and others | Around 100 km, lower edge |
| Pink | Molecular nitrogen | Below about 100 km |
During strong geomagnetic storms the auroral oval expands towards the equator, and red auroras that are rarely seen appear over mid-latitudes.
When and where to see it
The best places lie under the auroral oval: Yellowknife in Canada, Fairbanks in Alaska, Tromsø in Norway, Finnish Lapland and Iceland. Aim for the dark months from September to March, on clear nights with little moonlight, roughly between 10 p.m. and 2 a.m. Forecasts from NOAA's Space Weather Prediction Center and the Kp index (0–9) of geomagnetic activity help; the higher the Kp, the farther from the poles the aurora can be seen. During the Carrington Event of 1859 auroras were seen in the Caribbean and telegraph systems failed. In May 2024, near the peak of the roughly 11-year solar cycle, the strongest geomagnetic storm in about two decades (G5) brought auroras to southern Europe and the southern United States and was even caught by observatory cameras in South Korea. Planets with magnetic fields and atmospheres, such as Jupiter and Saturn, have auroras too.
FAQ
- Can you see the aurora from places like Korea or southern Europe?
- Only rarely, during very strong geomagnetic storms, when a faint red glow may be photographed low on the northern horizon. For a clear naked-eye display you need to travel to high latitudes.
- When is the best time to go aurora hunting?
- September to March on clear nights away from the full moon. Staying three or four nights or more improves your chances despite bad weather, and years near solar maximum are best.
Sources reviewed: 2026-10-26
References
- Akasofu, S.-I. (1964). The development of the auroral substorm. Planetary and Space Science, 12(4), 273–282.
- Tsurutani, B. T., Gonzalez, W. D., Lakhina, G. S., & Alex, S. (2003). The extreme magnetic storm of 1–2 September 1859. Journal of Geophysical Research, 108(A7), 1268.
- Eather, R. H. (1980). Majestic Lights: The Aurora in Science, History, and the Arts. American Geophysical Union.
- NOAA Space Weather Prediction Center. (2024). Aurora: Tutorial and 30-Minute Forecast. National Oceanic and Atmospheric Administration.