“Why are some auroras purple?”, Asks Kenza Stambouli on our Facebook page. Thank you all for participating in our “Question of the Week”; Every Friday, we answer one of them on the Science at Avenir website.

What causes aurora?

Polar light, called borealis in the northern hemisphere and southern in the southern hemisphere, is caused by the interaction of charged particles traveling in the solar winds with the Earth’s atmosphere. “Colored sails are visible when particles emitted by the Sun are moved up along the lines of the solar wind along the lines of the Earth’s magnetic field and collide with atoms in the upper atmosphere.“The European Space Agency (ESA) says. These collisions occur between altitudes of 80 and 1000 km. Depending on the atoms that are struck, the aurora can exhibit different colors: nitrogen gives blue and red colors. Is, or even violet, while the oxygen palette. There are traces of green and red, while hydrogen and helium are blues and mawaes.

Most often confined to the poles, the aurora can appear at lower latitudes depending on the intensity of the solar vagina. But the time they are observed is also important. Thus, 2700 years ago, the auroras appeared as Mesopotamia. We have evidence of this thanks to three rectangular tablets engraved between 679 and 655 BCE by astrologers from Babylon and Assyria, recently discovered and studied by Japanese astronomers. They show red light in the sky, and for the astronomers who analyzed them the astrologers matched the polar lights. To confirm this, they measured the amount of carbon 14 present in tree rings dating from the same period. And they found a rapid increase in carbon-14 concentration, which is associated with increased solar activity.

Dawn forecast a science still imprecise

Auroras are celestial events that are of particular interest in this activity and also important for tourist agencies. They organize a stay in areas conducive to dawn. Problem: You are never sure if you can see them. It is indeed still difficult to predict their occurrence, because it is necessary to be interested in solar weather. Progress has been made in recent years and thanks Satellites that monitor the sun And the development of its magnetic field, forecasting solar flares now appears to be an objective Admirable. They also observe the explosions that make it possible to evaluate their strength, their speed and their direction and therefore have to know if the Earth will be affected. Sites like SpaceWeather continuously record solar activity. However, and even if we know that a packet of particles will grow on Earth and attack its magnetic shield, it is still difficult to predict whether the cause aurora they will be intense … or even That will appear.