space velocity

The space velocity is the velocity of a star, with respect to the local standard of rest, expressed as components along three axes. The components are usually given as U (radially outward from the galactic center), V (in the direction of galactic rotation), and W (in the direction of the galactic north pole, i.e. perpendicular to the galactic plane), with positive signs if as indicated or negative signs if oppositely directed. The resultant space velocity is given by the Pythagoras theorem as √(U 2 + V 2 + W 2). In the case of the Sun, U = –9 km/s, V = +12 km/s, and W = +7 km/s, giving a space velocity of 17 km/s.