List all the known phenomena that affect the determination of the coordinates of stars from observations and should be taken into account when they want to find out the proper motion of stars on the celestial sphere, for which the coordinates determined at the moments of time, separated by an interval of at least a decade, are compared.
Refraction, aberration, annual and daily; precession; nutation: parallax annual.
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.