Science & history · Star guide
Alpha Centauri, the nearest star system
Alpha Centauri is the nearest star system to the Sun: three stars a little over four light-years away. To the naked eye the two bright ones merge into a single point, the third-brightest in the night sky.
About this picture
NASA/Goddard Space Flight Center Scientific Visualization Studio. Gaia DR2: ESA/Gaia/DPAC. Constellation figures based on those developed for the IAU by Alan MacRobert of Sky and Telescope magazine (Roger Sinnott and Rick Fienberg). NASA's page (opens in a new tab).
The map is a composite of 1.7 billion catalogued stars, not a photograph from one place: it shows stars far too faint for the eye, and no weather, Moon or city light. It is drawn here in this chart's projection, with each star where it was in 2000; the fastest-moving bright star has shifted about a minute of arc since, far less than a pixel here.
How to spot it: The brighter of the two Pointers beside the Southern Cross. Source (opens in a new tab)
Three stars
Alpha Centauri is three stars: two Sun-like ones that look like one, and a faint red dwarf that is the nearest star of all.
NASA describes (opens in a new tab) a system of three. Alpha Centauri A and B take 80 years to orbit each other; the third, Proxima Centauri, takes more than half a million years to circle the pair. At 4.25 light-years, Proxima is the nearest star to the Sun.
Proxima is a red dwarf (opens in a new tab), the smallest and coolest kind of main-sequence star and too faint to see with the unaided eye. It has at least one planet, Proxima b (opens in a new tab), about 1.27 times Earth's mass on an 11-day orbit in the star's habitable zone; whether it could support life is unknown, not least because Proxima often flares with intense ultraviolet light.
The bright pair is what you see. NASA calls Alpha Centauri (opens in a new tab) the closest main-sequence star visible to the unaided eye.
Sources for this section NASA Science, Our Nearest Celestial Neighbor? An Exotic 3-Star System (opens in a new tab); NASA Science, Star Types (opens in a new tab)
One point of light
To the eye, A and B merge into one star, the third-brightest in the sky.
The two bright stars are too close together on the sky to split by eye. ESA's Hipparcos table (opens in a new tab) ranks their combined light third among all stars, at a distance of 4.4 light-years.
The IAU's catalogue of star names (opens in a new tab) lists them separately: A is Rigil Kentaurus, magnitude −0.01; B is Toliman, magnitude 1.35; and C is Proxima Centauri, magnitude 11.01. NASA (opens in a new tab) uses the same names.
Sources for this section ESA, Hipparcos: The 50 Brightest Stars (opens in a new tab); IAU Working Group on Star Names, IAU Catalog of Star Names (IAU-CSN) (opens in a new tab); NASA Science, Our Nearest Celestial Neighbor? An Exotic 3-Star System (opens in a new tab)
How to find it
Alpha Centauri is the brighter of the two Pointers that lead to the Southern Cross.
With Hadar, beta Centauri, it forms the Pointers (opens in a new tab): two bright stars side by side that lead the eye to the Southern Cross. Alpha is the brighter of the two and, by this site's calculation (opens in a new tab), the farther from the Cross: about 16° from Acrux, against about 12° for Hadar.
It is a southern star. By this site's calculation (opens in a new tab) it never rises north of about 29°N, while from 35°S it climbs to about 64° up in the south and from far enough south it never sets. It is highest at about 9 p.m. local time in mid-June.
Sources for this section Ian Ridpath, Star Tales: Centaurus (opens in a new tab); Bright Star Catalogue, 5th Revised Ed. (Hoffleit & Warren 1991), as computed by this site's star engine (opens in a new tab)
Moving fast
Being so near, Alpha Centauri drifts across the background faster than any other bright star.
Nearby stars show the largest proper motions, ESA explains (opens in a new tab), because a given speed through space crosses a bigger angle on the sky when the star is close.
By this site's calculation (opens in a new tab) from its catalogued proper motion, Alpha Centauri moves 3.7 seconds of arc a year: the width of the full Moon in about 500 years, the fastest of any star in the catalogue brighter than magnitude 1.5.
Sources for this section ESA, How does Gaia study the Milky Way? (opens in a new tab); Bright Star Catalogue, 5th Revised Ed. (Hoffleit & Warren 1991), as computed by this site's star engine (opens in a new tab)
Where on Earth, and when
It rises from anywhere south of about 29°N.
South of about 29°S, it never sets.
It climbs at least 20° high, the finder's threshold for a suggestion, from anywhere south of about 9°N.
It is highest in the evening sky, at about 9 p.m. local time, in mid-June, from either hemisphere, wherever it rises. With daylight saving time, that is nearer 10 p.m. on the clock.
Worked out by this site from the Bright Star Catalogue, for a flat, clear horizon. Hills, buildings, haze and city light all cut into this; the air also lifts objects near the horizon by about half a degree. For your own place and night, use the sky finder.
Sources
- Astronomy NASA Science, Our Nearest Celestial Neighbor? An Exotic 3-Star System (opens in a new tab) for the three stars, their orbits, Proxima and its planet, the IAU names · checked 27 September 2026
- Astronomy NASA Science, Star Types (opens in a new tab) for red dwarfs and the nearest naked-eye main-sequence star · checked 27 September 2026
- Astronomy ESA, Hipparcos: The 50 Brightest Stars (opens in a new tab) for rank and combined distance · checked 27 September 2026
- Astronomy IAU Working Group on Star Names, IAU Catalog of Star Names (IAU-CSN) (opens in a new tab) for the IAU names and magnitudes · checked 2 October 2026
- History Ian Ridpath, Star Tales: Centaurus (opens in a new tab) for the Pointers · checked 27 September 2026
- Astronomy ESA, How does Gaia study the Milky Way? (opens in a new tab) for proper motion and distance · checked 27 September 2026
- Astronomy Bright Star Catalogue, 5th Revised Ed. (Hoffleit & Warren 1991), as computed by this site's star engine (opens in a new tab) for separations, northern limit, height, best month and proper motion
