What is proper motion?
A) It is the annual apparent motion of a star across the sky.
B) It is the motion of a star towards or away from us, revealed by Doppler shifts.
C) It is the orbital motion of a star around the Galaxy.
D) It is the apparent shift as we go to opposite sides of our orbit every six months.
E) It is the true, not apparent, motion of a star in space.
Answer: A