Alpha Centauri

α CentauriAlphaα Centauri ARigil KentaurusACentauriαα Cenα Centauri BAlpha Centauri A
Alpha Centauri (Latinized from α Centauri, abbreviated Alpha Cen or α Cen) is the closest star system to the Solar System at 4.37 ly from the Sun.wikipedia
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Proxima Centauri

Alpha Proximaits host starProxima
It is a triple star system, consisting of three stars: α Centauri A (officially Rigil Kentaurus ), α Centauri B (officially Toliman ), and α Centauri C (officially Proxima Centauri ).
Proxima Centauri forms a third component of the Alpha Centauri system, currently with a separation of about 12950 AU and an orbital period of 550,000 years.

Centaurus

Cena picture of himselfCentaur
Alpha Centauri A and B are Sun-like stars (Class G and K), and together they form the binary star Alpha Centauri AB. To the naked eye, the two main components appear to be a single star with an apparent magnitude of −0.27, forming the brightest star in the southern constellation of Centaurus and the third-brightest in the night sky, outshone only by Sirius and Canopus. To the naked eye, Alpha Centauri AB appears to be a single star, the brightest in the southern constellation of Centaurus.
Notable stars include Alpha Centauri, the nearest star system to the Solar System, its neighbour in the sky Beta Centauri, and V766 Centauri, one of the largest stars yet discovered.

List of brightest stars

brightest starsbrightest starone of the brightest stars
Alpha Centauri A and B are Sun-like stars (Class G and K), and together they form the binary star Alpha Centauri AB. To the naked eye, the two main components appear to be a single star with an apparent magnitude of −0.27, forming the brightest star in the southern constellation of Centaurus and the third-brightest in the night sky, outshone only by Sirius and Canopus.
Stellar brightness is traditionally based on the apparent visual magnitude as perceived by the human eye, from the brightest stars of 1st magnitude to the faintest at 6th magnitude. Since the invention of the optical telescope and the documenting of binary stars and multiple star systems, stellar brightness could be expressed as either individual (separate) or total (combined) magnitude. The table is ordered by combined magnitude of all naked eye components appearing as if it they were single stars. Such multiple star systems are indicated by parentheses showing the individual magnitudes of component stars bright enough to make a detectable contribution. For example, the double star Alpha Centauri has the total or combined magnitude of −0.27, while its two component stars have magnitudes of +0.01 and +1.33.

K-type main-sequence star

orange dwarfKK-type star
Alpha Centauri A and B are Sun-like stars (Class G and K), and together they form the binary star Alpha Centauri AB. To the naked eye, the two main components appear to be a single star with an apparent magnitude of −0.27, forming the brightest star in the southern constellation of Centaurus and the third-brightest in the night sky, outshone only by Sirius and Canopus.
Better known examples include Alpha Centauri B (K1 V) and Epsilon Indi.

G-type main-sequence star

yellow dwarfGG-type
Alpha Centauri A and B are Sun-like stars (Class G and K), and together they form the binary star Alpha Centauri AB. To the naked eye, the two main components appear to be a single star with an apparent magnitude of −0.27, forming the brightest star in the southern constellation of Centaurus and the third-brightest in the night sky, outshone only by Sirius and Canopus.
Besides the Sun, other well-known examples of G-type main-sequence stars include Alpha Centauri A, Tau Ceti, and 51 Pegasi.

Thomas Henderson (astronomer)

Thomas HendersonHenderson, ThomasProfessor Thomas Henderson
The large proper motion of Alpha Centauri AB was discovered by Manuel John Johnson, observing from Saint Helena, who informed Thomas Henderson at the Royal Observatory, Cape of Good Hope of it. The parallax of Alpha Centauri was subsequently determined by Henderson from many exacting positional observations of the AB system between April 1832 and May 1833.
Thomas Henderson FRSE FRS FRAS (28 December 1798 – 23 November 1844) was a Scottish astronomer and mathematician noted for being the first person to measure the distance to Alpha Centauri, the major component of the nearest stellar system to Earth, the first to determine the parallax of a fixed star, and for being the first Astronomer Royal for Scotland.

Alpha Crucis

Acruxα Crucisα Cru
Alpha Centauri was only the second binary star to be discovered, preceded by Alpha Crucis.
It is the southernmost first-magnitude star, 2.3 degrees more southerly than Alpha Centauri.

First magnitude star

brightestfirst magnitudefirst magnitude stars
To the naked eye, Alpha Centauri AB appears to be a single star, the brightest in the southern constellation of Centaurus.

Canopus

α Carinaea first magnitude starCanopean
Alpha Centauri A and B are Sun-like stars (Class G and K), and together they form the binary star Alpha Centauri AB. To the naked eye, the two main components appear to be a single star with an apparent magnitude of −0.27, forming the brightest star in the southern constellation of Centaurus and the third-brightest in the night sky, outshone only by Sirius and Canopus.
English explorer Robert Hues brought it to the attention of European observers in his 1592 work Tractatus de Globis, along with Achernar and α Centauri, noting: "Now, therefore, there are but three Stars of the first magnitude that I could perceive in all those parts which are never seene here in England. The first of these is that bright Star in the sterne of Argo which they call Canobus. The second is in the end of Eridanus. The third is in the right foote of the Centaure."

Crux

Southern CrossSouthern Cross constellationconstellation
some 4.5° west, points to the constellation Crux—the Southern Cross.
Alternatively, if a line is constructed perpendicularly between Alpha Centauri and Beta Centauri, the point where the above-mentioned line and this line intersect marks the Southern Celestial Pole.

Beta Centauri

Hadarβ Cenβ Centauri
It forms the outer star of The Pointers or The Southern Pointers, so called because the line through Beta Centauri (Hadar/Agena),
A line made from the other pointer, Alpha Centauri, through Beta Centauri leads to within a few degrees of Gacrux, the star at the north end of the cross.

Luhman 16

Luhman 16 (WISE 1049-5319)Luhman 16B
Alpha Centauri is inside the G-cloud, and its nearest known system is the binary brown dwarf system Luhman 16 at 3.6 ly.
These are the closest-known brown dwarfs and the closest system found since the measurement of the proper motion of Barnard's Star in 1916, and the third-closest-known system to the Sun (after the Alpha Centauri system and Barnard's Star).

Sirius

SothisDog StarSirius B
Alpha Centauri A and B are Sun-like stars (Class G and K), and together they form the binary star Alpha Centauri AB. To the naked eye, the two main components appear to be a single star with an apparent magnitude of −0.27, forming the brightest star in the southern constellation of Centaurus and the third-brightest in the night sky, outshone only by Sirius and Canopus.
This proximity is the main reason for its brightness, as with other near stars such as α Centauri and in contrast to distant, highly luminous supergiants such as Canopus, Rigel or Betelgeuse.

Binary star

spectroscopic binaryeclipsing binarybinary
Alpha Centauri A and B are Sun-like stars (Class G and K), and together they form the binary star Alpha Centauri AB. To the naked eye, the two main components appear to be a single star with an apparent magnitude of −0.27, forming the brightest star in the southern constellation of Centaurus and the third-brightest in the night sky, outshone only by Sirius and Canopus.
Orbital periods can be less than an hour (for AM CVn stars), or a few days (components of Beta Lyrae), but also hundreds of thousands of years (Proxima Centauri around Alpha Centauri AB).

Royal Observatory, Cape of Good Hope

Royal ObservatoryCape ObservatoryRoyal Observatory at the Cape of Good Hope
The large proper motion of Alpha Centauri AB was discovered by Manuel John Johnson, observing from Saint Helena, who informed Thomas Henderson at the Royal Observatory, Cape of Good Hope of it. The parallax of Alpha Centauri was subsequently determined by Henderson from many exacting positional observations of the AB system between April 1832 and May 1833.
The second HM Astronomer, Thomas Henderson, aided by his assistant, Lieutenant William Meadows, made the first observations that led to a believable stellar parallax, namely of Alpha Centauri.

Angular diameter

apparent diameterangular sizeapparent size
As seen from Earth, Proxima Centauri is 2.2° southwest from Alpha Centauri AB, about four times the angular diameter of the Moon.
The angular diameter of the Sun is also about 250,000 times that of Alpha Centauri A (it has about the same diameter and the distance is 250,000 times as much; the Sun is 4×10 10 times as bright, corresponding to an angular diameter ratio of 200,000, so Alpha Centauri A is a little brighter per unit solid angle).

Orbital period

periodsynodic periodsynodic
It has an estimated orbital period of approximately 12 Earth days – less than that of Mercury – with a semimajor axis of 0.10 AU and an eccentricity smaller than 0.24.
When describing orbits of binary stars, the orbital period is usually referred to as just the period. For example, Jupiter has a sidereal period of 11.86 years while the main binary star Alpha Centauri AB has a period of about 79.91 years.

List of nearest stars and brown dwarfs

passing starsnearest starsclosest stars
Alpha Centauri (Latinized from α Centauri, abbreviated Alpha Cen or α Cen) is the closest star system to the Solar System at 4.37 ly from the Sun.

Manuel John Johnson

Manuel Johnson
The large proper motion of Alpha Centauri AB was discovered by Manuel John Johnson, observing from Saint Helena, who informed Thomas Henderson at the Royal Observatory, Cape of Good Hope of it. The parallax of Alpha Centauri was subsequently determined by Henderson from many exacting positional observations of the AB system between April 1832 and May 1833.
While comparing his results with those of Nicolas Louis de Lacaille he noted the high proper motion of Alpha Centauri and communicated these to Thomas Henderson at the Royal Observatory, Cape of Good Hope.

Alpha Centauri in fiction

Alpha Centauri(3) Alpha CentauriAlpha Centauri A
Alpha Centauri in fiction
Alpha Centauri, a double star system with the binary designation Alpha Centauri AB, is the brightest visible object in the southern constellation Centaurus.

Breakthrough Starshot

StarChipBreakthrough Starshot initiativeSprites
Using current spacecraft technologies, crossing the distance between the Sun and Alpha Centauri would take several millennia, though the possibility of nuclear pulse propulsion or laser light sail technology, as considered in the Breakthrough Starshot program, could reduce the journey time to decades.
Breakthrough Starshot is a research and engineering project by the Breakthrough Initiatives to develop a proof-of-concept fleet of light sail spacecraft named StarChip, to be capable of making the journey to the Alpha Centauri star system 4.37 light-years away.

Star system

multiple star systemmultiple systemstriple star
It is a triple star system, consisting of three stars: α Centauri A (officially Rigil Kentaurus ), α Centauri B (officially Toliman ), and α Centauri C (officially Proxima Centauri ). Alpha Centauri (Latinized from α Centauri, abbreviated Alpha Cen or α Cen) is the closest star system to the Solar System at 4.37 ly from the Sun.
Alpha Centauri is a triple star composed of a main binary yellow dwarf pair (Alpha Centauri A and Alpha Centauri B), and an outlying red dwarf, Proxima Centauri. Both A and B form a physical binary star, designated as Alpha Centauri AB, α Cen AB, or RHD 1 AB, where the AB denotes this is a binary system. The moderately eccentric orbit of the binary can make the components be as close as 11 AU or as far away as 36 AU. Proxima is much further away (~15,000 AU) from α Cen AB than they are to each other. Although this distance is still comparatively small to interstellar distances, it is still debatable whether Proxima, whose orbital period would be more than 500,000 years, is gravitationally bound to α Cen AB.

Apparent magnitude

apparent visual magnitudemagnitudevisual magnitude
Alpha Centauri A and B are Sun-like stars (Class G and K), and together they form the binary star Alpha Centauri AB. To the naked eye, the two main components appear to be a single star with an apparent magnitude of −0.27, forming the brightest star in the southern constellation of Centaurus and the third-brightest in the night sky, outshone only by Sirius and Canopus.

Robert T. A. Innes

Robert InnesRobert Thorburn Ayton InnesDr Robert T A Innes
Alpha Centauri C was discovered in 1915 by Robert T. A. Innes, who suggested that it be named Proxima Centaurus, later amended to Proxima Centauri.
In 1915, he found a faint star fairly close to and sharing the same large proper motion with Alpha Centauri, which until then was believed to be the closest star system to the Sun.

61 Cygni

61 Cyg61 Cygni A61 Cyg A
He withheld his results, however, because he suspected they were too large to be true, but eventually published them in 1839 after Friedrich Wilhelm Bessel released his own accurately determined parallax for 61 Cygni in 1838.
His measurement was published only shortly before similar parallax measurements of Vega by Friedrich Georg Wilhelm von Struve and Alpha Centauri by Thomas Henderson that same year.