statistical parallaxThe mean parallax of a group of stars that are all at about the same distance and whose space velocities are randomly orientated. It is derived from the radial velocities and the tau components of the stars' proper motions: the tau component is measured perpendicular to the great circle joining a star to the solar apex. It is thus perpendicular to and independent of the Sun's motion, i.e. it results entirely from the motion of the star. The average velocity in one direction will equal that in any other direction. The average radial velocity is thus a measure of average velocity. The average distance is then found from the ratio of average radial velocity to average tau component.
statistical parallax[stə′tis·tə·kəl ′par·ə‚laks]
The mean parallax of a collection of stars that are all at approximately the same distance, as determined from their radial velocities and proper motions.