The aurora borealis, which would be more correctly called the aurora borealis, since it occurs in the polar regions of the Earth, is one of the most beautiful natural phenomena. The essence of this phenomenon lies in the fact that the solar wind, being deflected by the earth's magnetic field towards its poles, collides with the atoms of gases in the earth's atmosphere. In this collision, the gas atom passes into an excited state and releases energy in the form of a photon - a particle that does not have mass and charges. It is these photons that produce the effect of the aurora borealis.
The deeper the charged particles of the solar wind penetrate into the earth's atmosphere, the more often they collide with atoms, because the concentration of gas atoms noticeably increases as they approach the Earth's surface. Accordingly, the stronger and longer the northern lights will be.
The color of the aurora depends on two factors: the height at which the collision occurred; the type of gas, the atom of which has come to an excited state. For example, if the color is either red or green, it means that particles of the solar wind have come into contact with oxygen atoms. Accordingly, the red color means that it happened at a high altitude (over 200 kilometers above the Earth), and green - at medium altitudes (from 100 to 200 kilometers). If the color is blue or violet, this means that nitrogen atoms have entered an excited state. The photons formed when the atoms of other gases are excited are almost indistinguishable, since nitrogen and oxygen are the most massive components of the earth's atmosphere.
The difference in colors produced by photons of excited oxygen atoms is explained by the following pattern. If the colliding oxygen atom does not collide with another oxygen atom within one second, it will emit a green photon. If this collision does not occur within two whole minutes, it will emit a red photon. But in the event that the collision occurs faster than a second, no photon is formed at all. It is easy to understand that red color will turn out only at altitudes, more than 200 kilometers, where the concentration of atoms is negligible and their collisions rarely occur. Well, at an altitude less than 100 kilometers, collisions occur so often that an excited oxygen atom does not have time to remain intact even for a second, and no photon is formed.
Of course, the stronger the disturbances in the Sun's atmosphere, the stronger the solar wind fluxes are. Therefore, upon hearing about another solar flare, residents of the polar regions in the northern hemisphere, as well as winterers in Antarctica, must be prepared: after a while they will see a particularly strong and beautiful aurora.