Why, before spacecraft orbited the moon and photographed its far side, people could only see one half of it?

The period of rotation of the Moon around its axis is equal to the period of its revolution around the Earth, so that it always faces the Earth with the same side.

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.