As you know, auroras arise in the upper atmosphere of the Earth when exposed to particles of the solar wind.

As you know, auroras arise in the upper atmosphere of the Earth when exposed to particles of the solar wind. Why, then, can they be observed in polar night conditions, when even the upper atmosphere is not illuminated by the Sun?

If the trajectory of the solar wind particles were a straight line, then, like sunlight, they would not fall into the winter polar atmosphere, which is in the deep shadow of the Earth. But these particles have an electrical charge, and their trajectory is curved in the Earth’s magnetic field. Due to this, they enter the upper atmosphere at night, especially near the magnetic poles of the Earth, causing aurora there.