Why do astronomers measure a stars/cluster of stars proper motion and direction.?
First off this Bill character just threw out random garbage. Don’t take what he says to mean anything because it doesn’t. Second it seems you’re lacking in an understanding on stars and clusters of stars. The reasons for measuring the motion of stars and clusters is very extensive. I think first I need to distinguish the difference between just stars and star clusters. There are two types of clusters, Open clusters, which are very loosely bound collections of relatively young stars, and Globular clusters, which are more tightly bound large collections of older stars. Open clusters are generally found within the disk of the milky way and Globular clusters are found outside the disk, either above or below it. Knowing the motion of these clusters is important in gathering general knowledge of our galaxy. How it looks, where mass is, how it moves overall. Knowing the general structure and motion of our galaxy is a very important and pressing matter in galactic astronomy. Our lack of reason
