Radial velocity is a method used in astronomy to measure the speed at which a celestial object is moving either towards or away from an observer on Earth. This measurement is typically made by analyzing the Doppler shift in the light emitted or reflected by the object, which causes a shift in the observed wavelength. By measuring the radial velocity of stars, planets, and other celestial bodies, astronomers can determine important properties such as the mass of planets orbiting a star, the presence of binary star systems, and the structure and dynamics of galaxies. This information can provide valuable insights into the formation and evolution of celestial objects and help researchers better understand the underlying principles governing the universe.