BARNARD'S STAR

second nearest star to the Sun, at a distance of about 6 light-years. It is named for Edward Emerson Barnard, the American astronomer who discovered it in 1916. Barnard's star has the largest proper motion of any known star10.25 arc annually. It is a red dwarf star with a visual magnitude of 9.5; its intrinsic luminosity is only 1/2,300 that of the Sun. Because of its high velocity of approach, 108 km (67 miles) per second, Barnard's star is gradually coming nearer the solar system and by the year 11,800 will reach its closest point in distancenamely, 3.85 light-years. The star is of special interest to astronomers because its proper motion, observed photographically between the years 193881, has shown periodic deviations of 1 micrometre, or 0.02 of arc. This perturbation is interpreted as being caused by the gravitational pull of two planetary companions having orbital periods of 13.5 and 19 years, respectively, and masses of about two-thirds that of Jupiter. The existence of planetary bodies outside the solar system, however, remains unproved.