During the night from Sunday to Monday, November 6, impressive northern lights were observed in the sky. Threads of blue, orange and pink light, which were visible from the early evening in Auvergne or even in Pas-de-Calais, but also in the United Kingdom and as far as Ukraine. A rare sight for these territories, less accustomed to large, colorful sails than the north of the continent.
How are the Northern Lights formed?
At the origin of this phenomenon, “the arrival last night of a wave of solar particles”, deciphers science popularizer Pierre Henriquet on Twitter (renamed X). Because if the Northern Lights appear on Earth, they find their source near the sun, confirms Nathalie Huret, professor of atmospheric physico-chemistry at Clermont-Auvergne University. “The sun is continually active. But when it experiences strong eruptions, it ejects plasma, a hot gas composed of charged particles, towards the Earth.” This plasma then reaches our planet, and “collides with the Earth’s magnetic field, which will excite the particles in our atmosphere.”
This is what will produce light, and form the northern lights in the sky. The colors differ depending on the atoms stimulated. Oxygen thus gives a green color, and nitrogen gives more blue and purple tones. “And when a large coronal mass ejection (of solar plasma) takes place, we then speak of a solar storm” explains the director of the Clermont-Ferrand globe physics observatory.
Why are we seeing them in France?
If the phenomenon is rare in France, it is “not unprecedented”, assures Nathalie Huret. Since the start of 2023, the Northern Lights have decorated the French sky on several occasions. The last time was just a few weeks ago, on the night of Sunday September 24 to 25. Multicolored light nets could also be observed in February and April 2023.
According to the figures, however, the Northern Lights are observable “every ten years” on average in France, continues Nathalie Huret. So how can we explain the multiplication of the phenomenon? For the researcher, the answer is simple: “It denotes intense solar activity.” “In general, it’s true, the Northern Lights mainly occur in what are called “polar horns”, at the North and South Poles. But as the sun is very active at the moment, a lot of particles luckily arrived in the direction of the Earth, and at very high speed, which explains why we were able to observe the Northern Lights at a medium altitude, in France. » This is also what justifies colors closer to mauve than green, the composition of the atmosphere being “a little different in mid-latitude”.
Will they become more and more frequent?
Can the French hope to observe more and more northern lights in the sky? Not impossible, replies Nathalie Huret. “Really, it depends on the solar cycle.” That is to say a period which lasts approximately eleven years, and during which the activity of the sun varies. Today, the sun is in its 25th cycle, which began in December 2019. “According to current forecasts, it should be at its peak of activity in 2025,” explains the professor. However, the closer we get to this maximum, the more we will have significant and intense particle ejections.”
In the months to come, new colored waves could therefore decorate the French sky. “We’re not going to have them every two days, but there’s a better chance,” admits the researcher. On the other hand, it will always be necessary to combine different factors: the solar flare must be oriented in the right direction, and with sufficient speed and intensity.”
In any case, to hope to enjoy the show, “you will have to get as far away from light sources as possible,” recalls Nathalie Huret. “As well as looking north, since the majority of particles rush toward the solar horn.” And if the natural phenomenon offers impressive images, “it can also have important consequences, with significant impacts”, emphasizes the professor of atmospheric physics. “Aurorae can notably disrupt the waves, and therefore telecommunications or even electrical networks.” In 1989, a major solar storm caused a total blackout in Quebec, plunging 6 million people into darkness.
This article is originally published on liberation.fr