At a distance of just 6.0 light years, Barnard's Star is the second closest star to the Earth, considering the Alpha Centauri system as a unit). However, at magnitude 9.54, it is not even close to being visible to the naked eye. It is a typical red dwarf star, appearing in the northernmost part of the constellation Ophiuchus.

The proper motion of Barnard's Star imaged over five years (Paul Mortfield & Stefano Cancelli)
Proper Motion

Barnard's Star's fame derives from a variety of properties, chief among them its proper motion, i.e. its angular annual movement across our line of sight as seen against the distant stellar background. The star was named after its discoverer, noted astronomer Edward Emerson Barnard, who found in 1916 that Barnard's Star has the greatest proper motion of any star: a whopping 10.4" per year. While that may not seem like much, it amounts to a quarter of a degree in a human lifetime, roughly the angular diameter of the full Moon. This huge angular displacement results from a truly high speed of 139 km/sec relative to the Sun. Barnard's Star is approaching the solar system rapidly, and will be closest at 3.8 light-years around 11,800 A.D.

Physical Properties

This dim, cool (3170 K), red dwarf has a luminosity merely 0.0035 times the Sun's, a diameter only 20% of the Sun's, and a mass of merely 17% the Sun's. Barnard's Star has a metal content only 10% the Sun's. That low metallicity, coupled with its high velocity, makes it a "subdwarf" that belongs ancient halo of our Galaxy. It is merely passing through the local solar neighborhood. Barnard's Star is clearly old, born before supernovae had enriched the interstellar medium with the amount of metals seen today. Stars slow down as they age, and Barnard's Star's long rotation period of 130 days - some five times longer than the Sun's - also attests to its age. Its low internal temperature and resultant feeble energy generation rate give it an incredibly long lifespan. Indeed, no class M dwarf born in the history of our galaxy has yet expired.

The closest star systems to our Sun. (ESO)
Nevertheless, Barnard's Star still has some magnetic activity, occasionally flaring due to the release of magnetic field energy. It has an active X-ray corona heated magnetically to two million K (as does the Sun), and probably starspots (from which its rotation period is inferred). Flares from magnetic effects have given Barnard's Star its variable-star designation, V2500 Ophiuchi. Observations of a particularly bright 1998 flare suggested a flare temperature of 8000 K, more than twice Barnard's Star's normal temperature - surprising because such intense stellar activity is not expected around stars of such age.

Possible Planets

Part of the star's notoriety is that it was among the first to be announced - in 1963 by Peter van de Kamp - as having orbiting planets, the result of perceived wobbles in its proper motion. Van de Kamp's initial suggestion was 1.6 Jupiter mass planet at 4.4 AU in a slightly eccentric orbit. Later in 1969 he suggested two planets of 1.1 and 0.8 Jupiter masses in periods of 12 and 26 years. Alas, the "discovery" was an error, as the apparent positional shifts were caused by adjustments in the telescope lens. Negative results for planetary companions continued throughout the 1980s and 90s, the latest based on interferometric work with Hubble space telescope in 1999, and on radial velocity observations in 2003.

The controversy did heighten the profile of Barnard's Star, however; during the period that the planetary claim was accorded credibility, the star's fame in science fiction grew. It was adopted as a target for Project Daedalus - a study conducted by the British Interplanetary Society between 1973 and 1978 to design a plausible interstellar unmanned spacecraft only current and near-future technologies, such as nuclear fusion for propulsion.

[Adapted from STARS by Jim Kaler, Professor Emeritus of Astronomy, University of Illinois]