Northern lights are the result of disturbances in the Earth’s magnetosphere caused by the solar wind. The solar wind consists of charged particles – these particles’ trajectories are altered by the magnetosphere and are pointed toward the upper atmosphere layers – thermosphere and/or exosphere. This results in ionization and excitation of atmosphere elements that emit light of varying color and complexity.

Auroras usually appear in the region 10 to 20 degrees from the Earth’s geomagnetic poles. In northern latitudes, this effect is known as aurora borealis and is visible from areas around the Arctic, such as Alaska, Canada, Greenland, Iceland, Finland, Siberia, etc. But on rare occasions when the K-index reaches high values (around 8-9) the auroras can be seen as far south as the Mediterranean and the southern states of the US. This scenario happened during the night of 10/11 May 2024, so the northern lights were easily visible in the southern part of Poland and also much further south.

Northern lights 2024 May 10
Norther lights 2024 May 10

Auroras seen from high latitudes may be watched directly overhead, but from farther away, they illuminate the poleward horizon as faint red or greenish glow. Large geomagnetic storms can occasionally enlarge the auroral oval – it is most common during the peak of the 11-year sunspot cycle.

Interesting fact is that most of the planets in the Solar System, some natural satellites, and even comets also host auroras.

Auroral light color depends on the element that was excited. At lower latitudes only the high part of the aurora can be spotted, and these are usually red. This color comes from excited oxygen that emits at 630nm. The low concentration of atoms and lower sensitivity of eyes at this wavelength make this color visible only under highly intense solar activity.

At lower altitudes green emission at 557.7nm dominates and suppresses the 630nm (red) light. Auroras seen in green light are also much better visible due to the fact, that the human eye is much more sensitive to this wavelength than in red. At yet lower altitudes atomic oxygen is uncommon and molecular nitrogen takes over in producing visible light, radiating in both red and blue parts of the spectrum, with 428nm (blue) being dominant. Blue and purple emissions are then typical for the lower edges of “curtains”.

Northern lights 2024 May 10
Northern lights 2024 May 10

Auroras in southern Poland are very rare, and the ones visible to the naked eye are extremely uncommon. The one from May 10th, 2024 was quite intense, and despite some clouds, I was able to take a few pictures.

During its maximum, it was easily seen with the naked eye as a red-purple glow in the sky, or behind the clouds. Also, some vertical bands could be seen at some moments. The dynamics were quite large, and significant changes could sometimes be noticed within 5-10 seconds.

All photos above were shot with a Sony A7 III camera and a Tamron 17-28 f/2.8 lens. The exposure time was 15 seconds and ISO was set to 400.