For this, it is necessary that the given object (planet or black hole) be part of a close binary system, and the second object is a visible star. Due to the movement of both objects around the center of mass, the visible component shows periodic deviations in the celestial sphere. The same method is applied when observing the line spectrum.
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.