linguistic:paraphrasing, structural:scholar_edition
Kinematics

The radial velocity of Vega is the component of this star's motion along the line-of-sight to the Earth. Movement away from the Earth will cause the light from Vega to shift to a lower frequency (toward the red), or to a higher frequency (toward the blue) if the motion is toward the Earth. Thus the velocity can be measured from the amount of shift of the star's spectrum. Precise measurements of this blueshift give a value of −13.9 ± 0.9 km/s. The minus sign indicates a relative motion toward the Earth.

Motion transverse to the line of sight causes the position of Vega to shift with respect to the more distant background stars. Careful measurement of the star's position allows this angular movement, known as proper motion, to be calculated. Vega's proper motion is 202.03 ± 0.63 milliarcseconds (mas) per year in right ascension —the celestial equivalent of longitude —and 287.47 ± 0.54 mas/y in declination, which is equivalent to a change in latitude. The net proper motion of Vega is 327.78 mas/y, which results in angular movement of a degree every 11,000 years.

In the galactic coordinate system, the space velocity components of Vega are (U, V, W) = (−16.1 ± 0.3, −6.3 ± 0.8, −7.7 ± 0.3) km/s, for a net space velocity of 19 km/s. The radial component of this velocity—in the direction of the Sun—is −13.9 km/s, while the transverse velocity is 12.9 km/s. Although Vega is at present only the fifth-brightest star in the night sky, the star is slowly brightening as proper motion causes it to approach the Sun. Vega will make its closest approach in an estimated 264,000 years at a perihelion distance of 13.2 ly (4.04 pc).

Based on this star's kinematic properties, it appears to belong to a stellar association called the Castor Moving Group. However, Vega may be much older than this group, so the membership remains uncertain. This group contains about 16 stars, including Alpha Librae, Alpha Cephei, Castor, Fomalhaut and Vega. All members of the group are moving in nearly the same direction with similar space velocities. Membership in a moving group implies a common origin for these stars in an open cluster that has since become gravitationally unbound. The estimated age of this moving group is 200 ± 100 million years, and they have an average space velocity of 16.5 km/s.