The proper motions of stars are
A) easy to measure for most stars on photographs taken 6 months apart.
B) noticeable to the unaided eye as a gradual shift of the constellations westward over the course of a month or two.
C) easy to observe with the unaided eye over the course of an hour or two.
D) difficult to measure even on photographs taken several years apart for any but the nearest stars.

Question

Quizplus · Accepted Answer

Proper motions of stars are very small because of the vast distances involved, making them difficult to measure even on photographs taken several years apart, and this is generally only noticeable for the nearest stars.

The Proper Motions of Stars Are