In 1916, the American astronomer E. E. Barnard measured its proper motion as 10.3 arcseconds per year. This is the largest-known proper motion of any star relative to the Sun. At a distance of about 1.8 parsecs from the Solar System, or just under six light-years, Barnard's Star is the nearest known star in the constellation Ophiuchus, and the fourth-closest known individual star to the Sun, after the three components of the Alpha Centauri system. Despite its proximity, Barnard's Star, at a dim apparent magnitude of about nine, is not visible with the unaided eye; however, it is much brighter in infrared light than it is in visible light.