Sirius

system

Sirius is the brightest star in Earth's night sky, 8.6 light-years away in Canis Major. It is a binary: the hot blue-white main-sequence star Sirius A, and Sirius B — a white dwarf, the Earth-sized, extraordinarily dense burnt-out core of a star that has already died. The two orbit their common centre of mass every 50.1 years on a markedly elliptical path, swinging between about 8 and 31 AU apart. No planets have been confirmed; precise astrometry has ruled out further companions down to a few tens of Jupiter masses.

Open in 3D viewSee Sirius in the live, interactive 3D map

Key facts

Type

Binary star

Distance

8.6 light-years

Mutual orbit

50.1 yr

Confirmed planets

Science

Classification

Type: Binary star system
Stars: Sirius A (A1V main sequence) + Sirius B (DA white dwarf)

Members

Stars: 2
Confirmed planets: None

Distance & orbit

Distance: 8.6 light-years · one of the Sun's nearest stellar neighbours
Orbital period: 50.1 years · e = 0.59; the pair's separation swings between ~8 and ~31 AU
Age: ~240 million years · estimated — a young system, far younger than the Sun

How we know

Note: Sirius A's brilliance is partly its nearness — it is intrinsically luminous, but also one of the Sun's closest neighbours. Sirius B is a white dwarf: no telescope has ever imaged the 'surface' of any white dwarf, so it is shown as an honest hot-white point, with its physics in the Science tab. No planets are confirmed, so none are shown. On the map the system is placed at a usable distance — the real gap is 8.6 light-years.

Discovery & history

Method: Naked-eye star
Name: 'Sirius' is the Greek Seirios, 'scorching' — the Dog Star of Canis Major, the Greater Dog. Its stars are Sirius A and Sirius B (nicknamed 'the Pup').

Sirius has blazed in the sky since prehistory, but its companion was found by reason before sight. In 1844 Friedrich Bessel deduced from a wobble in Sirius's motion that an unseen massive body orbited it; on 31 January 1862 Alvan Graham Clark first glimpsed that faint companion — Sirius B — while testing a new refractor. In 1915 its spectrum revealed it as a hot yet tiny star: the first white dwarf recognised for what it is, and a preview of the Sun's eventual fate.

Images

The Sirius binary — brilliant Sirius A with the white dwarf Sirius B (the tiny dot at lower left), imaged by Hubble — NASA, ESA, H. Bond (STScI) & M. Barstow (Univ. of Leicester) (public domain) · Wikimedia Commons

The Sirius system in X-rays — the white dwarf Sirius B is the brighter source (Chandra X-ray Observatory) — NASA / SAO / CXC (public domain) · Wikimedia Commons

Where to find it — Sirius blazes in Canis Major, the Greater Dog (IAU constellation chart) — IAU / Sky & Telescope, R. Sinnott & R. Fienberg (CC BY 3.0) · Wikimedia Commons

Images from open archives · credit shown per image