Figure 3-55Radial and Transverse Velocities of a Star The actual velocity of a star (or other object) can be separated into radial and transverse motions. The speed of the star toward or away from Earth in kilometers per hour is its radial velocity. This motion creates a Doppler shift (see Section 3-2) of the entire star’s spectrum. The speed in kilometers per hour perpendicular to the radial velocity is called its transverse velocity, which does not affect the star’s spectrum. The angular motion of the star across the celestial sphere (that is, in the direction of its transverse velocity) is called proper motion.