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Nature can sometimes manifest itself in all its brutality: volcanic eruptions, colossal earthquakes or devastating tsunamis. Fortunately, this one also reminds us of its beauty along with other phenomena that can leave us speechless. Count among these the Northern Lights, these veils of light dancing in the night skies. For centuries they have captivated the imagination of our ancestors.
In Norse mythology, for example, the ancient Scandinavians were convinced that the Northern Lights were caused by the armor of the Valkyries, celestial warriors. These lit the path of dead warriors to Valhalla, the warriors' paradise, where they would be welcomed by the god Odin. Among the Inuit, the northern lights were the spirits of hunted animals or represented messages from their ancestors. Certain other Native American tribes (Ojibwe or Athabaskans), for their part, sometimes attributed them to evil spirits or demons.
Today, we obviously know that this extraordinary atmospheric phenomenon finds its origins elsewhere. It results from a complex interaction between charged particles emitted by the Sun and the Earth's magnetic fields. Much less poetic, but just as interesting.
From the Sun to the Earth: the cosmic route of particles
It all starts with our only star in the solar system: the Sun. This, in its bubbling activity, emits an incessant flow of charged particles , known as solar wind. This solar blast, composed mainly of electrons and protons, propagates through space at sidereal speeds, reaching up to 2,000 km/s.< /p>
From time to time, the Sun engages in more spectacular flares, called coronal mass ejections (CMEs). These sudden explosions project colossal quantities of charged particles into space. These particularly intense solar storms send waves of these particles towards Earth which can reach our planet in just a few hours. Whatever their mode of emission, these solar particles travel around 150 million kilometers, a journey that lasts between two and three days, before meeting the Earth. Upon their arrival, they collide with the magnetosphere, the invisible shield that protects our planet from harmful radiation.
The Earth's magnetic field, like a giant funnel, channels charged particles toward the magnetic poles, guiding them along magnetic field lines. This phenomenon occurs primarily in auroral zones, circular regions centered around the magnetic poles, where the density of magnetic field lines is particularly high. This is where the magic happens !
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Atmospheric alchemy: the birth of an aurora
Heading towards Earth , charged particles from the solar wind and coronal mass ejections impact the gas molecules of the Earth's atmosphere, essentially oxygen and nitrogen. These collisions trigger intense excitation within the atoms, ionizing them and propelling them toward higher energy states. When these excited atoms return to their normal state, they release the accumulated energy in the form of photons, particles of light. The color of this light depends on the altitude at which the interaction occurs and the type of excited gas.
Below 100 km At altitude, it is nitrogen that takes center stage. Collisions with this gas produce blue and purple glows, giving the auroras these completely mesmerizing hues. Between 100 and 240 km, oxygen is involved, giving rise to the famous green lights. Beyond 240 km, it is again oxygen which is the cause, but this time in tones red, deep and intense< /strong>.
The other fascinating aspect of this phenomenon is its variability. Their intensity and appearance are not constant, but closely linked to solar activity. Periods of high solar activity considerably amplify the auroras. These celestial shows intensify and become visible well beyond the polar circles and sometimes reach countries far from the polar circles. This was the case last year in France where some lucky people were able to see Mont Saint-Michel embraced by these famous lights (see video below).
Where and when to admire the auroras
To admire the northern lights, you must look towards the clear night skies , far from any light pollution. The regions most conducive to this contemplation are located in high latitudes, where night reigns for a long time during the winter seasons.
Norway, Sweden and Finland, s& ;#8217;establish as privileged destinations for observing these dancing veils of light. Northern Canada, Scotland, Alaska and Russia also offer spectacular panoramas. If you think that the Northern Lights are an exclusively Nordic phenomenon, think again! New Zealand, too, is lucky to see its sky sometimes decorated with this spectacle. The southern tip of the South Island also offers the possibility of admiring the auroras australis, the cousins of the northern lights, located in the southern hemisphere.
To maximize your chances of witnessing the appearance of the aurora, it is recommended to choose dates close to the spring equinoxes (March) and autumn (September). Indeed, during these periods, the Earth tilts optimally towards the Sun, thus increasing the probabilities of observing them. However, it is important to keep in mind that nature is capricious and the appearance of the Northern Lights is not a constant.
In addition to being staggeringly beautiful, the Northern Lights remind us that our planet Earth does not orbit alone in space, but is in permanent interaction with it and all the cosmic forces which pass through it. A good little reminder, which makes us remember one thing: we are nothing, or very little compared to the immensity of the Universe. Simple little dust in front of him, which will remain, in any case, completely indifferent to what we can do here on earth. It never hurts to remind yourself of it.
- The Northern Lights are caused by cosmic particles in coming from the Sun.
- These interact with the gases present in the Earth's atmosphere and release energy in the form of light.
- This phenomenon only appears in certain areas of the world and at specific times.
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