“I didn’t believe it for a second,” writes a photographer who managed to immortalize the northern lights on Sunday in Pas-de-Calais. A rare phenomenon, these celestial lights usually associated with the north and south poles were seen over the northern half of France on Sunday through Tuesday nights.
Called the “aurora borealis” in the northern hemisphere and the “austral lights” in the south, these colorful glows are the result of particles ejected from the sun passing through Earth’s magnetic field.
“An aurora borealis occurs when the sun expels matter”
Above all, we must understand that the Earth is surrounded by a magnetic field, “an invisible shield that protects us from the solar wind”, indicates the Canadian space agency. This field deflects particles arriving from our star, which could endanger life on Earth. But, sometimes, certain charged particles (electrons and protons), coming from the sun, go through the wall and the terrestrial magnetic field “directs them towards the poles”.
“An aurora borealis is produced when the sun ejects matter,” sums up Éric Lagadec, president of the French society for astronomy and astrophysics, on BFMTV. “And if this material is ejected in the direction of Earth, it’s very energetic, it can interact with the atmosphere.”
As they pass through the upper atmosphere, charged particles “collide with the atoms in them” such as nitrogen and oxygen, details unisciel university online, “this energy input excites the atoms to high energy levels and de-energized by emitting light”.
These collisions between solar particles and terrestrial gases “produce tiny flashes that fill the sky with colored light,” details the Canadian space agency. “As billions of lightning bolts strike in sequence, the aurora appears to move or ‘dance’ across the sky.”
“Green is the most common color”
The color that the aurora borealis emits “is specific to the excited atom, and since the concentrations of oxygen and nitrogen change with altitude, the color also changes,” says Unisciel.
The color of the aurora is related to the altitude at which it appears, the composition and density of the atmosphere in that place but also “the level of energy involved”, also writes the Canadian space agency. “Green is the most common color seen from the ground and is produced when charged particles collide with oxygen molecules at altitudes of 100 to 300 km,” he explains.
The pink or dark red colors are “produced by nitrogen molecules at altitudes of about 100 km” and at altitudes of 300 to 400 km, “collisions with oxygen atoms produce red auroras.” Finally, hydrogen and helium molecules can produce blue and purple auroras.
“The more active the sun is, the further south the auroras will appear”
“In general, the northern lights are seen quite close to the poles, because they interact with the magnetic field,” explains Éric Lagadec. In the diagrams that represent the magnetic field around the Earth, we can see a sphere that surrounds the planet and folds at the poles, where the particles that arrive from the sun are redirected.
If the recent aurora borealis could be observed at latitudes further south than usual, it means “there really was a very large solar flare,” says the astrophysicist. “As a general rule, the more active the sun is, the more southern auroras will appear,” the Canadian space agency also writes.
It is not the first time that the northern lights have been observed further south of the poles, in 2015 impressive photos of these lights were taken in the French sky. And the phenomenon could be reproduced shortly, emphasizes Éric Lagadec.
“The sun has an 11-year activity cycle, so it will peak in 2025, so maybe with a bit of luck we can see more by then.”
Source: BFM TV
