““The one thing we know is that planet Earth does keep moving in the direction of the constellation Leo at a rate of 390 km per second; the motion of the Earth around the Sun, which obviously changes directions, happens to involve a velocity of about 30 km per second, and does not easily lend itself to our best measurement techniques. Rather, we have trouble separating it from the motion with which our solar system orbits the center of the Milky Way. Once we include this, we arrive at the velocity of the Milky way with respect to the system where the universe as a whole is at rest; this velocity comes in at 600 km per second.””
