Radial velocity Radial velocity The radial velocity of an object with respect to a given point is the rate of change of the distance between the object and the point. That is, the radial velocity is the component of the object's velocity that points in the direction of the radius connecting the object and the point. In astronomy, the point is usually taken to be the observer on Earth, so the radial velocity then denotes the speed with which the object moves away from or approaches the Earth. In astronomy, radial velocity is often measured to the first order of approximation by
Angular velocity a true vector, rather than just a pseudo-vector. The only non-obvious property of the above addition is commutativity. This can be proven from the fact that the velocity tensor "W" (see below) is skew-symmetric, so that formula_34 is a rotation matrix which can be expanded as formula_35. The composition of rotations is not commutative, but formula_36 is commutative to first order, and therefore formula_37. Notice that this also defines the substraction as the addition of a negative vector. Given a rotating frame of three unit coordinate vectors, all the three must have the same angular speed at each instant. In