Barnard’s Star is the fourth closest star to Earth. Only the sun, Proxima Centauri, and the binary (double) star Alpha Centauri are closer. Barnard’s Star lies about 6 light-years away. One light-year is the distance light travels in a vacuum in a year, about 9.46 trillion kilometers. As seen from Earth, Barnard’s Star lies in the northern part of the constellation Ophiuchus, the Serpent Holder. The star takes its name from the American astronomer Edward Emerson Barnard, who discovered it in 1916.
Astronomers classify Barnard’s Star as a type of small, faint star called a red dwarf. It has about 17 percent of the sun’s mass (amount of matter). The diameter of Barnard’s Star measures about 15 to 20 percent that of the sun. Its reddish color results from relatively low surface temperatures, around 3000 K. One kelvin (K) equals one Celsius degree above absolute zero (–273.15 °C). Because of its small size and cool surface, Barnard’s Star gives off about 1/2,500 as much light as does the sun. It cannot be seen with the unaided eye.
Astronomers have observed that Barnard’s Star has sudden, intense increases in brightness called flares that fade within a few minutes. These flares probably resemble solar flares on the sun. But because Barnard’s Star is much smaller than the sun, the flares have a much more pronounced effect on its overall brightness. For this reason, astronomers refer to Barnard’s Star as a flare star.
Barnard’s Star exhibits proper motion—that is, it appears to move in relation to the backdrop of stars in the sky. In fact, Barnard’s Star shows the most dramatic proper motion of any known star. In about 200 years, the star drifts a distance across the sky equal to the diameter of the full moon as seen from Earth. In about 10,000 years, the movement of Barnard’s Star will carry it to within 3.8 light-years of the sun.
See also Barnard, Edward Emerson ; Fixed star ; Star (table: The 10 known stars nearest Earth) .
