2023-11-14 19:26:02
The French sky lit up with bright colors in September, then once more in early November. What is this miracle?
This phenomenon, which is called the aurora borealis, is quite common in the Nordic countries, but much rarer in France. It has been observed for a very long time, but was only fully explained in 2008!
Ingredients
As with any physical phenomenon, a few ingredients are necessary for the appearance of an aurora borealis. The first is the sun, which is mainly responsible for this spectacle, although it is only visible when it is quite dark!
The second is the Earth’s magnetic field. It is created by the movements of molten iron and nickel in the Earth’s core. It is this same principle of moving metal that explains the operation of all electric motors and generators that produce electricity.
The last is our atmosphere, whose composition depends on altitude: nitrogen, oxygen, hydrogen are mixed, but, the higher we go, the more we find a significant proportion of oxygen.
The mechanism
Have you ever heard of magnetic storms? The sun is a star in constant activity. It regularly projects matter over long distances, notably electrically charged particles which can strike the Earth.
These particles might be harmful to life on Earth. Fortunately, we are protected by the Earth’s magnetic field! In the same way that it directs compass needles towards the north, it channels charged particles sent by the sun towards the north and south poles.
When these particles encounter the atmosphere, they collide with the atoms that compose it. This gives them additional energy which allows them to emit a light particle. It is the same phenomenon which explains why certain objects are fluorescent (see Actuailes n°92). Depending on the type of atom, the color will be different: green or red for oxygen; blue, red or purple for nitrogen.
This is how we obtain magnificent skies of varied colors. The bigger the solar flare, the bigger the solar storm and the more auroras can be seen at significant distances from the equator. Thus, in November, the auroras might be seen as far away as the south of France and Italy.
Malo du Bretoux
News n°167 – November 15, 2023
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