The northern lights change color due to the nature of the molecules present in Earth's atmosphere. Each color corresponds to a type of ionized molecule reacting with solar particles.
The colors of the northern lights mainly come from the different gases present in our atmosphere. Oxygen is largely responsible for those famous green and red hues: when it is excited by particles from the sun, it emits a very intense green light (the typical color of the auroras) in the lower layers of the atmosphere, and higher up it shifts to a reddish hue. Nitrogen, on the other hand, often causes bluish, purple, or pink shades, giving the auroras those varied colors that are much less common but highly appreciated. It is thus thanks to this nice gaseous cocktail of oxygen and nitrogen that the northern lights are dressed in different colors.
The solar wind constantly swings towards Earth a flow of charged particles such as electrons and protons. When these particles reach our atmosphere, they collide with and excite the gaseous atoms present. It is mainly these collisions that give rise to the magnificent colors of the auroras. The more active the sun is with its solar flares or magnetic storms, the more energy the particles it releases have, which alters the types of atoms affected and therefore the observed hues. With highly energetic particles, one can even see less common shades like deep red or purple. When they are calmer, it will be more of a pale green, the most classic color of the northern lights.
The altitude at which the auroras occur greatly determines their colors. High up in the atmosphere, around 200 kilometers and higher, it is often oxygen that comes into play, giving a rather red hue. When descending to 100 to 200 kilometers, oxygen expresses itself more in shades of bright green, which is what is most frequently seen from the ground. And if we go even lower, to about 90 kilometers, it is nitrogen that takes over and colors the aurora blue or violet. Therefore, it is truly the altitude, depending on the molecules present, that offers this beautiful natural gradient.
The Northern Lights vary depending on where you are. Near the magnetic poles (auroral zones such as Alaska, Canada, Iceland, Scandinavia), intense auroras with bright green colors are frequently observed. The further you move away from these regions, the rarer and more diffuse the sightings become, with colors often appearing pinkish or red at mid-latitudes. Seasons also have an influence: during the equinoxes of spring and autumn, the tilt of the Earth facilitates increased interaction between solar particles and the atmosphere, intensifying the phenomenon. Conversely, in the heart of winter or summer, auroral activity may slightly wane.
The reddish colors of the northern lights are particularly rare because they only appear during solar interactions with oxygen located at very high altitudes, typically beyond 200 km.
Some Scandinavian legends viewed the auroras as manifestations of gods or warriors, while the Inuit peoples believed they were created by spirits playing ball with walrus skulls.
The ideal time to observe the Northern Lights is generally around the equinoxes, in March and September, as the Sun's magnetic activity interacts more intensely with that of the Earth during these times.
Although rarer, the southern lights appear in the southern hemisphere and share the same creation mechanism as the northern lights.
The periods around the equinoxes (March-April and September-October) generally provide the best chances. During these times, geomagnetic activity tends to increase, thereby enhancing the frequency and visibility of the auroras.
The northern lights primarily occur near the poles, where the Earth's magnetic field directs solar particles straight into the atmosphere. This phenomenon explains their higher frequency and intensity in polar regions.
Some accounts describe a faint sound similar to crackling or whispering during intense auroras. However, these sounds remain rare and are still the subject of scientific studies for confirmation.
A clear sky, far from urban light pollution, provides the best conditions for observation. Cold temperatures and a clear, cloudless sky also allow for better visibility.
It is difficult to precisely predict the color of an aurora borealis as it mainly depends on the atmospheric composition and the energy of solar particles. However, by knowing the dominant presence of certain gases like oxygen and nitrogen, one can anticipate the possible hues.
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