Barnard's Star

Star

Barnard's Star — a dim red dwarf (M4V) just 5.96 light-years away: the closest single star to the Sun and the second-closest star system after Alpha Centauri. Famous as 'Barnard's Runaway Star' for the largest proper motion of any star, it races ~10.4 arcseconds across the sky each year. Ancient and slow-burning (7–12 billion years old), it hosts a compact family of at least four confirmed sub-Earth planets — all closer than Mercury and far too hot for liquid water.

Open in 3D viewSee Barnard's Star in the live, interactive 3D map

Key facts

Mass

3.22 × 10²⁹ kg

0.162 M☉

Radius

128,704 km

18% of the Sun's radius

Surface temperature

3,195 K (2922 °C)

Luminosity

1.34 × 10²⁴ W

Spectral type

M4V (red dwarf)

Science

Physical

Mass: 3.22 × 10²⁹ kg · 0.162 M☉
Radius: 128,704 km · 18% of the Sun's radius
Density: 36,080 kg/m³ · 36× water
Spectral type: M4V (red dwarf)

Rotation

Note: Rotates slowly, roughly once every 130 days — a sign of its great age. Famous instead for its motion THROUGH space: at 10.4 arcseconds per year it has the largest proper motion of any known star.

Composition

By mass: A small, fully convective ball of hydrogen and helium — so cool (~3195 K) that most of its light is infrared: it puts out only about 0.35% of the Sun's total energy, and just ~0.04% of its visible light. Metal-poor and very old, it is a quiet, inactive red dwarf (a rare flare aside).

Temperature

Surface: 3,195 K (2922 °C)

Radiation & temperature

Luminosity: 1.34 × 10²⁴ W · 0.0035 L☉
Surface temperature: 3,195 K (2922 °C)
Peak wavelength: 907 nm · near-infrared (mostly invisible to the eye)

Discovery & history

Discovered: January 1, 1916
By: Edward Emerson Barnard
Name: Named for Edward Emerson Barnard, who measured its record proper motion in 1916. Far too faint for the naked eye, it carries no ancient name — only its catalogue designations (GJ 699).

The faint star was catalogued in the 19th century, but in 1916 Edward Emerson Barnard measured its proper motion at a record 10.3 arcseconds per year — the largest of any star — and it has carried his name and the nickname 'Runaway Star' ever since. From the 1960s Peter van de Kamp claimed to see gas-giant planets in its astrometric wobble, but those were spurious instrumental effects and were refuted. The first REAL planet, b, was confirmed by ESO's ESPRESSO spectrograph in October 2024, and a full four-planet family followed in 2025.

Images

Where to find it — Barnard's Star in Ophiuchus, the Serpent-Bearer (IAU chart) — too faint (V=9.5) to see with the naked eye — IAU / Sky & Telescope, R. Sinnott & R. Fienberg (CC BY 3.0) · Wikimedia Commons

Images from open archives · credit shown per image