Barnard's Star, also known occasionally as Barnard's "Runaway" Star, is a very low-mass red dwarf star approximately 6 light-years away from Earth in the constellation of Ophiuchus. In 1916, American astronomer E. E. Barnard measured its proper motion as 10.3 arcseconds per year, which remains the largest known proper motion of any star relative to the Sun. At a distance of about 1.8 parsecs, or just under six light-years, Barnard's Star is the nearest known star in Ophiuchus, the second-closest known star system to the Sun, 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 magnitude 9 is not visible with the unaided eye. It is, however, much brighter in the infrared spectrum. Barnard's Star has been the subject of much study and has probably received more attention from astronomers than any other M dwarf star due to its proximity and favourable location for observation near the celestial equator. Research has focused on stellar characteristics, astrometry, and refining the limits of possible extrasolar planets. Although it is an ancient star, observations suggest that Barnard's Star still experiences flare events.