The sun and planets in the solar system are used to help propel and guide spacecraft to their ultimate destinations. These bodies provide "gravity assists," commonly called "slingshot" trajectories, ...
Einstein’s theory of general relativity explains how gravity works. It says that massive objects like planets, stars, or ...
A POPULAR exposition of the doctrine of Relativity and what it implies: for this the world has been crying since the astronomers announced that the stars had proved it true. Here is an excellent ...