Understading Gravity at Long Distances Hi all, I have a simple curiosity and expect some simple answers. The star next to Sun does not have much gravitational influence on it. If it would have any influence it would have been felt by planets also. My questions are, 1. Then how do stars in a constellation stay together when they possibly cannot influence each other 'much' because of the huge distance between them? 2. How do clusters of galaxies form when there are utterly enormous distances between them? In other words, the stars that are at the boundary of a galaxy do not have any 'power' to influence the boundary stars of a galaxy that is very very far away from them. So how do galaxies interact with each other?