Why is the sphere of fixed stars preserved in the system of the world of N. Copernicus?

In the era of N. Copernicus, they could not yet measure the distance to the stars and their own motion, so he believed that the stars are located at the same distance from the Earth.

Remember: The process of learning a person lasts a lifetime. The value of the same knowledge for different people may be different, it is determined by their individual characteristics and needs. Therefore, knowledge is always needed at any age and position.