When and why is day as long as night?

As you know, in summer the day is much longer than the night, and in winter, on the contrary, the night is much longer than the day. But this transition occurs gradually, and therefore in the fall and spring there comes a moment when day is equal to night. And this happens around March 20 and September 22. This is due to the fact that the earth revolves around the sun and around its axis, the angle at which the sun’s rays fall on the earth changes.