The Fixed (?) Stars
At a recent astronomical seminar, I was reminded by a speaker that our term, the “fixed stars” is not really correct. Stars do move across the sky, their motion being a combination of two measurable quantities, "radial velocity”, or motion in the line of sight, and "proper motion", motion across the line of sight. These motions are extremely slow, although they can be measured with accurate astronomical instruments. To the unaided eye, however, the stars appear to be stationary, unless studied over a lengthy period of time.