Earth is rotating around it's axis, then around the sun, then around the center of the galaxy etc. But how can we know how fast it is moving in space? Let's take two objects in space, we know that the distance between them is changing, we can determine which one moves slower, the one who's time runs faster is moving slower (time dilation). Basically we can find a frame of reference where v = 0 (where object doesn't move in space and where is no time dilation (at least it is very small). So how fast the Earth is moving in space and what is our time dilation?