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This article is about "α Centauri".
For "a Centauri", see .
For "A Centauri", see .
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Location of Alpha Centauri in Centaurus (right-click on starmap to enlarge)
Alpha Centauri (α Cen); also known as Rigil Kent ( ) or Toliman, is the brightest
in the southern
star in the night sky. The Alpha Centauri system is located 1.34
from the Sun, making it the
to our . Although it appears to the unaided eye as a single object, Alpha Centauri is actually a
(designated Alpha Centauri AB or α Cen AB) whose combined
of -0.27 makes it the third brightest star (other than the ) seen from
after the -1.46 magnitude
and the -0.72 magnitude .
Its component stars are named Alpha Centauri A (α Cen A), with 110% of the mass and 151.9% the luminosity of the , and Alpha Centauri B (α Cen B), at 90.7% of the Sun's mass and 44.5% of its luminosity. During the pair's 79.91-year orbit about a common center, the distance between them varies from about that between
and the Sun to that between
and the Sun.
A third star, known as , Proxima, or Alpha Centauri C (α Cen C), is probably gravitationally associated with Alpha Centauri AB. Proxima is at the slightly smaller distance of 1.29
from the Sun, making it the closest star to the Sun even though it is not visible to the naked eye. The separation of Proxima from Alpha Centauri AB is about 0.06 , 0.2 light years or 15,000
(AU); equivalent to 400 times the size of 's orbit.
The Alpha Centauri system has been reported to contain one planet, the Earth-sized , which would be the closest known
to Earth, but its existence has been questioned.
"Alpha Centauri" is the name given to what appears as a single
to the naked eye and the
star in the southern constellation of . At -0.27v , it is fainter only than
and . The next brightest star in the night sky is . Actually a multiple star system, its two main stars are Alpha Centauri A (α Cen A) and Alpha Centauri B (α Cen B), usually defined to identify them as the different components of the binary α Cen AB. A third companion— (or Proxima or α Cen C)—has a distance much greater than the observed separation between stars A and B and is probably gravitationally associated with the AB system. As viewed from Earth, it is located at an
of 2.2° from the two main stars. If it were bright enough to be seen without a telescope, Proxima Centauri would appear to the naked eye as a star separate from α Cen AB. Alpha Centauri AB and Proxima Centauri form a visual . Direct evidence that Proxima Centauri has an elliptical orbit typical of binary stars has yet to be found. Together all three components make a triple , referred to by double-star observers as the
(or multiple star), α Cen AB-C.
Component sizes and colors. Shows the relative sizes and colors of stars in the Alpha Centauri system and compares them with those of the Sun.
Alpha Centauri A is the principal member, or primary, of the , being slightly larger and more luminous than the Sun. It is a solar-like
star with a similar yellowish color, whose
G2 V. From the determined mutual orbital parameters, Alpha Centauri A is about 10% more massive than the Sun, with a radius about 23% larger. The
( v·sin i ) of this star is 2.7 ± 0.7 km·s-1, resulting in an estimated rotational period of 22 days, which gives it a slightly faster rotational period than the Sun's 25 days. When considered among the individual
in the sky (excluding the ), Alpha Centauri A is the fourth brightest at -0.01 magnitude, being fractionally fainter than Arcturus at -0.04v magnitude.
Alpha Centauri B is the companion star, or secondary, of the , and is slightly smaller and less luminous than the Sun. It is a main-sequence star of spectral type K1 V, making it more an orange color than the primary star. Alpha Centauri B is about 90% the mass of the Sun and 14% smaller in radius. The projected rotational velocity ( v·sin i ) is 1.1 ± 0.8 km·s-1, resulting in an estimated rotational period of 41 days. (An earlier, 1995 estimate gave a similar rotation period of 36.8 days.) Although it has a lower luminosity than component A, star B emits more energy in the
of B varies on a short time scale and there has been at least one observed flare. Alpha Centauri B at 1.33v magnitude would be twenty-first in brightness if it could be seen independently of Alpha Centauri A.
Alpha Centauri C, also known as , is of
M5 Ve or M5 VIe, suggesting this is either a small main-sequence star (Type V) or
(VI) with . Its B-V
is +1.90 and its mass is about 0.123  (), or 129 .
Together, the bright visible components of the
system are called Alpha Centauri AB (α Cen AB). This "AB" designation denotes the apparent gravitational centre of the main binary system relative to other companion star(s) in any . "AB-C" refers to the orbit of Proxima around the central binary, being the distance between the centre of gravity and the outlying companion. Some older references use the confusing and now discontinued designation of A×B. Because the distance between the Sun and Alpha Centauri AB does not differ significantly from either star, gravitationally this binary system is considered as if it were one object.
studies, , and stellar rotation (), are all consistent with the α Cen system being similar in age to, or slightly older than, the Sun, with typical ages quoted between 4.5 and 7 billion years (). Asteroseismic analyses that incorporate the tight observational constraints on the stellar parameters for α Cen A and/or B have yielded age estimates of 4.85 ± 0.5 Gyr, 5.0 ± 0.5 Gyr, 5.2–7.1 Gyr, 6.4 Gyr, and 6.52 ± 0.3 Gyr. Age estimates for stars A and B based on chromospheric activity (Calcium H & K emission) yield 4.4–6.5 Gyr, whereas gyrochronology yields 5.0 ± 0.3 Gyr.
View of Alpha Centauri from the
The two Alpha Centauri AB binary stars are too close together to be resolved by the naked eye, because the angular separation varies between 2 and 22 arcsec, but through much of the orbit, both are easily resolved in binoculars or small 5 cm (2 in) telescopes.
In the southern hemisphere, Alpha Centauri forms the outer star of The Pointers or The Southern Pointers, so called because the line through
(Hadar/Agena), some 4.5 west, points directly to the
 — the . The Pointers easily distinguish the true Southern Cross from the fainter
known as the .
South of about , Alpha Centauri is
and never sets below the horizon. Both stars, including Crux, are too far south to be visible for mid-latitude northern observers. Below about
to the equator (roughly ,
in Mexico, ,
of Spain) during the northern summer, Alpha Centauri lies close to the southern horizon. The star
each year at midnight on 24 April or 9 p.m. on 8 June.
As seen from Earth,
lies 2.2° southwest from Alpha Centauri AB. This is about four times the
of the Full Moon, and almost exactly half the distance between Alpha Centauri AB and . Proxima usually appears as a deep-red star of 13.1v
in a poorly populated star field, requiring moderately sized telescopes to see. Listed as V645 Cen in the , this -type
can unexpectedly brighten rapidly to about 11.0v or 11.09V magnitude. Some amateur and professional astronomers regularly monitor for outbursts using either optical or radio telescopes.
English explorer
brought Alpha Centauri to the attention of European observers in his 1592 work Tractatus de Globis, along with Canopus and , 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 . The
is in the end of Eridanus. The third [Alpha Centauri] is in the right foote of the Centaure."
The binary nature of Alpha Centauri AB was first recognized in December 1689 by astronomer and Jesuit priest . The finding was made incidentally while observing a passing
from his station in . Alpha Centauri was only the second binary star system to be discovered, preceded only by . By 1752, French astronomer
positional measurements using a . Later,
made the first
observations in 1834. Since the early 20th century, measures have been made with .
By 1926, South African astronomer
calculated the approximate
close to those now accepted for this system. All future positions are now sufficiently accurate for visual observers to determine the relative places of the stars from a binary star . Others, like the Belgian astronomer D. Pourbaix (2002), have regularly refined the precision of any new published orbital elements.
The two bright stars are (left) Alpha Centauri and (right) . The faint red star in the center of the red circle is .
Taken with
f/1.8 lens with 11 frames stacked, each frame exposed 30 seconds.
Alpha Centauri is the closest star system to the . It lies about 4.37
in distance, or about 41.5 trillion kilometres, 25.8 trillion miles or 277,600 AU. Scottish astronomer
made the original discovery from many exacting observations of the trigonometric
of the AB system between April 1832 and May 1833. He withheld the results because he suspected they were too large to be true, but eventually published in 1839 after
released his own accurately determined parallax for
in 1838. For this reason, Alpha Centauri is considered as the second star to have its distance measured because it was not formally recognized first. Alpha Centauri is inside the , and the nearest known system to it is
at 3.6 light years.
Scottish astronomer
discovered
in 1915 by blinking photographic plates taken at different times during a dedicated
survey. This showed the large proper motion and parallax of the star was similar in both size and direction to those of Alpha Centauri AB, suggesting immediately it was part of the system and slightly closer to us than Alpha Centauri AB. Lying 4.24 light-years away, Proxima Centauri is the
to the Sun. All current derived distances for the three stars are from the
obtained from the
star catalog (HIP).
Alpha Centauri distance estimates
Henderson (1839)
Woolley et al. (1970)
1.346±0.013
4.39±0.04
Gliese & Jahreiss (1991)
749.0±4.7
1.335±0.008
4.355±0.027
41.2±0.26
van Altena et al. (1995)
749.9±5.4
1.334±0.01
4.349+0.032
Perryman et al. (1997) (A and B) (Hipparcos)
742.12±1.40
1.3475±0.0025
4.395±0.008
41.58±0.08
Perryman et al. (1997) (A and B) (Tycho)
S?derhjelm (1999)
747.1±1.2
1.3385+0.0022
4.366±0.007
41.3±0.07
van Leeuwen (2007) (A)
754.81±4.11
1.325±0.007
4.321+0.024
40.88±0.22
van Leeuwen (2007) (B)
796.92±25.90
1.25±0.04
RECONS TOP100 (2012)
747.23±1.17
1.3383±0.0021
4.365±0.007
41.29±0.06
Non-trigonometric distance estimates are marked in italic. The most precise estimate is marked in bold.
Apparent and true orbits of Alpha Centauri. The A component is held stationary and the relative orbital motion of the B component is shown. The apparent orbit (thin ellipse) is the shape of the orbit as seen by an observer on Earth. The true orbit is the shape of the orbit viewed perpendicular to the plane of the orbital motion. According to the radial velocity vs. time
the radial separation of A and B along the line of sight had reached a maximum in 2007 with B being behind A. The orbit is divided here into 80 points, each step refers to a timestep of approx. 0.99888 years or 364.84 days.
With the orbital period of 79.91 years, the A and B components of this
can approach each other to 11.2 , equivalent to 1.67 billion km or about the mean distance between the Sun and , or may recede as far as 35.6 AU (5.3 billion km—approximately the distance from the Sun to ). This is a consequence of the binary's moderate
e = 0.5179. From the , the total mass of both stars is about 2.0 —or twice that of the Sun. The average individual stellar masses are 1.09 M☉ and 0.90 M☉, respectively, though slightly higher masses have been quoted in recent years, such as 1.14 M☉ and 0.92 M☉, or totalling 2.06 M☉. Alpha Centauri A and B have
of +4.38 and +5.71, respectively.
theory implies both stars are slightly older than the Sun at 5 to 6 billion years, as derived by both mass and their spectral characteristics.
Viewed from Earth, the apparent orbit of this binary star means that the separation and
are in continuous change throughout the projected orbit. Observed stellar positions in 2010 are separated by 6.74  through the P.A. of 245.7°, reducing to 6.04 arcsec through 251.8° in 2011. Next closest approach will be in February 2016, at 4.0 arcsec through 300°. Observed maximum separation of these stars is about 22 arcsec, while the minimum distance is 1.7 arcsec. Widest separation occurred during February 1976 and the next will be in January 2056.
In the true orbit, closest approach or
was in August 1955, and next in May 2035. Furthest orbital separation at
last occurred in May 1995 and the next will be in 2075. The apparent distance between the two stars is rapidly decreasing, at least until 2019.
Main article:
The much fainter
named Proxima Centauri, or simply Proxima, is about 15,000
away from Alpha Centauri AB. This is equivalent to 0.24  or 2.2 trillion kilometres—about 5% the distance between Alpha Centauri AB and the Sun. Proxima is likely gravitationally bound to Alpha Centauri AB, orbiting it with a period between 100,000 and 500,000 years. However, it is also possible that Proxima is not gravitationally bound and thus moving along a
with respect to Alpha Centauri AB. The main evidence for a bound orbit is that Proxima's association with Alpha Centauri AB is unlikely to be coincidental, because they share approximately the same motion through space. Theoretically, Proxima could leave the system after several million years. It is not yet certain whether Proxima and Alpha Centauri are truly gravitationally bound.
Proxima is a red dwarf of
M5.5V with an
of +15.53, which is only a small fraction of the Sun's luminosity. By mass, Proxima is calculated as 0.123 ± 0.06 M☉ (rounded to 0.12 M☉) or about one-eighth that of the Sun.
Stars closest to the , including Alpha Centauri (25 April 2014).
All components of Alpha Centauri display significant
against the background sky, similar to the first magnitude stars
and . Over the centuries, this causes the apparent stellar positions to slowly change. Such motions define the high-proper-motion stars. These stellar motions were unknown to ancient astronomers. Most assumed that all stars were immortal and permanently fixed on the , as stated in the works of the philosopher Aristotle.
in 1718 found that some stars had significantly moved from their ancient
positions. For example, the bright star
(α Boo) in the constellation of
showed an almost 0.5° difference in 1800 years, as did the brightest star, , in
(α CMa). Halley's positional comparison was 's catalogue of stars contained in the
whose original data included portions from an earlier catalog by
during the 1st century . Halley's proper motions were mostly for northern stars, so the southern star Alpha Centauri was not determined until the early 19th century.
Scottish-born observer
in the 1830s at the Royal Observatory at the Cape of Good Hope discovered the true distance to Alpha Centauri. He soon realised this system displayed an unusually high proper motion, and therefore its observed true velocity through space should be much larger. In this case, the apparent stellar motion was found using 's astrometric observations of , by the observed differences between the two measured positions in different epochs. Using the
(HIP) data, the mean individual proper motions are -;mas/yr or -3.678 arcsec per year in
and +481.84 mas/yr or 0.4;arcsec per year in . As proper motions are cumulative, the motion of Alpha Centauri is about 6.1  each century, and 61.3  or 1.02 each . These motions are about one-fifth and twice, respectively, the diameter of the . Using
the mean radial velocity has been determined to be 25.1 ± 0.3 km/s towards the Solar System.
As the stars of Alpha Centauri approach us, the measured proper motion and trigonometric parallax slowly increase. Changes are also observed in the size of the semi-major axis of the orbital , increasing by 0.03 arcsec per century. This change slightly shortens the observed orbital period of Alpha Centauri AB by some 0.006 years per century. This small effect is gradually decreasing until the star system is at its closest to us, and is then reversed as the distance increases again. Consequently, the observed
of the stars are subject to changes in the
over time, as first determined by W. H. van den Bos in 1926. Some slight differences of about 0.5% in the measured proper motions are caused by Alpha Centauri AB's orbital motion.
Apparent motion of Alpha Centauri relative to
Based on these observed proper motions and radial velocities, Alpha Centauri will continue to gradually brighten, passing just north of the
or , before moving northwest and up towards the
and away from the . By about 29,700 , in the present-day constellation of , Alpha Centauri will be 1.00  or 3.26  away. Then it will reach the stationary radial velocity (RVel) of 0.0 km/s and the maximum apparent magnitude of -0.86V (which is comparable to present-day magnitude of ). However, even during the time of this nearest approach, the apparent magnitude of Alpha Centauri will still not surpass that of
(which will brighten incrementally over the next 60,000 years, and will continue to be the brightest star as seen from Earth for the next 210,000 years).
The Alpha Centauri system will then begin to move away from the Solar System, showing a positive radial velocity. Due to visual , about 100,000 years from now, these stars will reach a final
and slowly disappear among the countless stars of the Milky Way. Here this once bright yellow star will fall below naked-eye visibility somewhere in the faint present day southern constellation of
(this unusual location results from the fact that Alpha Centauri's orbit around the galactic centre is highly tilted with respect to the plane of the ).
In about 4000 years, the
of Alpha Centauri will mean that from the point of view of Earth it will appear close enough to
to form an optical . Beta Centauri is in reality far more distant than Alpha Centauri.
Until the 1990s, technologies did not exist that could detect planets outside the . Since then, exoplanet-detection capabilities have steadily improved to the point where Earth-mass planets can be detected.
Further information:
On 16 October 2012, researchers, mainly from the
and from the , announced that an Earth-mass () planet had been likely detected in orbit around Alpha Centauri B using the
technique. Over three years of observations had been needed for the difficult analysis, finding the planet orbiting very close to the host star at just 0.04 AU and completing one orbit every 3.236 days. It is not in Alpha Centauri B's habitable zone, with a surface temperature estimated to be 1200 ° (about 1500 K), far too hot for liquid
and also above the melting temperatures of many
. For comparison, the surface temperature of , the hottest planet in the , is 462 °C (735 K). Alpha Centauri Bb has a
of 1.13 .
The Alpha Centauri B planetary system
(in order from star)
1.13 ± 0.09 
3.2357 ± 0.0008
On 25 March 2015, a scientific paper by Demory et al. published transit results for Alpha Centauri B using the
for a total of 40 hours. Although the team could rule out, with 96.6% confidence, transit events for Alpha Centauri Bb (which does not preclude its existence, merely the fact that it is in the same plane as the Sun and Alpha Centauri B), they evidenced a transit event possibly corresponding to a planetary body with different orbital parameters. This planet would most likely orbit Alpha Centauri B with an orbital period of 20.4 days or less, with only a 5% chance of it having a longer orbit. The median average of the likely orbits being 12.4 days with an impact parameter of around 0–0.3. Its orbit would likely have an eccentricity of 0.24 or less. If confirmed, this planet would be called Alpha Centauri Bc. This planet would also still be far too close to its parent star to harbour life.
The discovery of , including similar binary systems (), raises the possibility that additional planets may exist in the Alpha Centauri system. Such planets could orbit Alpha Centauri A or Alpha Centauri B individually, or be on large orbits around the binary Alpha Centauri AB. Because both the principal stars are fairly similar to the Sun (for example, in age and ), astronomers have been especially interested in making detailed searches for planets in the Alpha Centauri system. Several established planet-hunting teams have used various
methods in their searches around these two bright stars. All the observational studies have so far failed to find any evidence for
In 2009, computer simulations (then unaware of the close-in planet Bb) showed that a planet might have been able to form near the inner edge of Alpha Centauri B's habitable zone, which extends from 0.5 to 0.9 AU from the star. Certain special assumptions, such as considering that Alpha Centauri A and B may have initially formed with a wider separation and later moved closer to each other (as might be possible if they formed in a dense ) would permit an accretion-friendly environment farther from the star. Bodies around A would be able to orbit at slightly farther distances due to A's stronger gravity. In addition, the lack of any brown dwarfs or gas giants in close orbits around A or B make the likelihood of terrestrial planets greater than otherwise. Theoretical studies on the detectability via radial velocity analysis have shown that a dedicated campaign of high-cadence observations with a 1–m class telescope can reliably detect a hypothetical planet of 1.8  in the habitable zone of B within three years.
Radial velocity measurements of Alpha Centauri B with
spectrograph ruled out planets of more than 4 M⊕ to the distance of the habitable zone of the star (orbital period P = 200 days).
Alpha Centauri is envisioned as the first target for unmanned . Crossing the huge distance between the Sun and Alpha Centauri using current spacecraft technologies would take several millennia, though the possibility of
technology could cut this down to a matter of decades.
Early computer-generated models of planetary formation predicted the existence of
around both Alpha Centauri A and B, but most recent numerical investigations have shown that the gravitational pull of the companion star renders the accretion of planets very difficult. Despite these difficulties, given the similarities to the Sun in , star type, age and probable stability of the orbits, it has been suggested that this stellar system could hold one of the best possibilities for harbouring
on a potential planet.
In the Solar System both Jupiter and Saturn were probably crucial in perturbing
into the inner Solar System. Here, the comets provided the inner planets with their own source of water and various other ices. In the Alpha Centauri system
may have influenced the planetary disk as the Alpha Centauri system was forming, enriching the area around Alpha Centauri A and B with volatile materials. This would be discounted if, for example, Alpha Centauri B happened to have gas giants orbiting Alpha Centauri A (or conversely, Alpha Centauri A for Alpha Centauri B), or if the stars B and A themselves were able to perturb comets into each other's inner system as Jupiter and Saturn presumably have done in the Solar System. Such icy bodies probably also reside in
of other planetary systems, when they are influenced gravitationally by either the gas giants or disruptions by passing nearby stars many of these icy bodies then travel starwards. There is no direct evidence yet of the existence of such an Oort cloud around Alpha Centauri AB, and theoretically this may have been totally destroyed during the system's formation.
To be in the star's , any suspected planet around Alpha Centauri A would have to be placed about 1.25  away []– about halfway between the distances of Earth's orbit and 's orbit in the  – so as to have similar planetary temperatures and conditions for liquid water to exist. For the slightly less luminous and cooler Alpha Centauri B, the habitable zone would lie closer at about 0.7 AU (100 million km), approximately the distance that
is from the Sun.
With the goal of finding evidence of such planets, both Proxima Centauri and Alpha Centauri AB were among the listed "Tier 1" target stars for 's
(SIM). Detecting planets as small as three Earth-masses or smaller within two
of a "Tier 1" target would have been possible with this new instrument. The SIM mission, however, was cancelled due to financial issues in 2010.
Looking toward the sky around Orion from Alpha Centauri with
generated by
Viewed from near the Alpha Centauri system, the sky would appear very much as it does for an observer on Earth, except that Centaurus would be missing its brightest star. The Sun would be a yellow +0.5 visual magnitude star in eastern
of Alpha Centauri's current
at 02h 39m 35s +60° 50′ (2000). This place is close to the 3.4 magnitude star . An interstellar or alien observer would find the \/\/ of Cassiopeia had become a /\/\/ shape
nearly in front of the
in Cassiopeia.
lies less than a degree from
in the otherwise unmodified
and is with -1.2 a little fainter than from Earth but still the brightest star in the Alpha Centauri sky.
is also displaced into the middle of , outshining , whereas both
are shifted northwestward relative to
(which barely moves, due to its great distance)- giving the
appearance.
From Proxima itself, Alpha Centauri AB would appear like two close bright stars with the combined magnitude of -6.8. Depending on the binary's orbital position, the bright stars would appear noticeably divisible to the naked eye, or occasionally, but briefly, as single unresolved star. Based on the calculated , the
of Alpha Centauri A and B would be -6.5 and -5.2, respectively.
Artist's rendition of the view from a hypothetical airless planet orbiting Alpha Centauri A
An observer on a hypothetical planet orbiting around either Alpha Centauri A or Alpha Centauri B would see the other star of the binary system as an intensely bright object in the night sky, showing a small but discernible disk.
For example, some theoretical planet orbiting about 1.25 AU from Alpha Centauri A (so that the star appears roughly as bright as the Sun viewed from the Earth) would see Alpha Centauri B orbit the entire sky once roughly every one year and three months (or 1.3(4) ), the planet's own . Added to this would be the changing apparent position of Alpha Centauri B during its long eighty-year elliptical orbit with respect to Alpha Centauri A (comparable in speed to
here). Depending on the position on its orbit, Alpha Centauri B would vary in apparent magnitude between -18.2 (dimmest) and -21.0 (brightest). These visual magnitudes are much dimmer than the observed -26.7
for the Sun as viewed from the Earth. The difference of 5.7 to 8.6 magnitudes means Alpha Centauri B would appear, on a linear scale, 2500 to 190 times dimmer than Alpha Centauri A (or the Sun viewed from the Earth), but also 190 to 2500 times brighter than the -12.5 magnitude full
as seen from the Earth.
Also, if another similar planet orbited at 0.71 AU from Alpha Centauri B (so that in turn Alpha Centauri B appeared as bright as the Sun seen from the Earth), this hypothetical planet would receive slightly more light from the more luminous Alpha Centauri A, which would shine 4.7 to 7.3 magnitudes dimmer than Alpha Centauri B (or the Sun seen from the Earth), ranging in apparent magnitude between -19.4 (dimmest) and -22.1 (brightest). Thus Alpha Centauri A would appear between 830 and 70 times dimmer than the Sun but some 580 to 6900 times brighter than the full Moon. During such planet's orbital period of 0.6(3) , an observer on the planet would see this intensely bright companion star circle the sky just as we see with the 's planets. Furthermore, Alpha Centauri A
of approximately eighty years means that this star would move through the local
as slowly as
with its eighty-four year period, but as the orbit of Alpha Centauri A is more elliptical, its apparent magnitude will be far more variable. Although intensely bright to the eye, the overall illumination would not significantly affect climate nor influence normal plant .
An observer on the hypothetical planet would notice a change in orientation to
reference points commensurate with the binary orbit periodicity plus or minus any local effects such as
Assuming this hypothetical planet had a low orbital inclination with respect to the mutual orbit of Alpha Centauri A and B, then the secondary star would start beside the primary at 'stellar' . Half the period later, at 'stellar' , both stars would be opposite each other in the sky. Then, for about half the planetary year the appearance of the night sky would be a darker blue – similar to the sky during totality at any total . Humans could easily walk around and clearly see the surrounding terrain, and reading a book would be quite possible without any artificial light. After another half period in the stellar orbit, the stars would complete their orbital cycle and return to the next stellar conjunction, and the familiar day and night cycle would return.
The colloquial name of Alpha Centauri is Rigel Kent or Rigil Kent, short for Rigil/Rigel Kentaurus, the romanization of the Arabic name ??? ???????? Rijl Qan?ūris, from the phrase Rijl al-Qan?ūris "the foot of the ". This is sometimes further abbreviated to Rigel, though that is ambiguous with , which is also called Rigel. Although the short form Rigel Kent is common in English, the stars are most often referred to by their
Alpha Centauri.
Distances of the
from 20,000 years ago until 80,000 years in the future
A medieval name is Toliman, whose etymology may be Arabic ??????? al-?ulmān "the ostriches". During the 19th century, the northern amateur popularist Elijah H. Burritt used the now-obscure name Bungula, possibly coined from "β" and the
ungula ("hoof"). Together, Alpha and Beta Centauri form the "Southern Pointers" or "The Pointers", as they point towards the Southern Cross, the
of the constellation of .
In , 南門 Nán Mén, meaning , refers to an asterism consisting of α Centauri and . Consequently, α Centauri itself is known as 南門二 Nán Mén ?r, the Second Star of the Southern Gate.
of northwestern , Alpha and
are Bermbermgle, two brothers noted for their courage and destructiveness, who speared and killed Tchingal "The Emu" (the ). The form in
is Bram-bram-bult.
Equal values of parallax and its error for A and B.
Weighted parallax based on parallaxes from van Altena et al. (1995) and S?derhjelm (1999).
Spellings include Rigjl Kentaurus, , "Ulugh Beighi Tabulae Stellarum Fixarum", Tabulae Long. ac Lat. Stellarum Fixarum ex Observatione Ulugh Beighi, Oxford, 1665, p. 142., Hyde T., "In Ulugh Beighi Tabulae Stellarum Fixarum Commentarii", op. cit., p. 67., Portuguese Riguel Kentaurus da Silva Oliveira, R., , Artigos: Planetario Movel Inflavel AsterDomus.
Hoffleit+ (1991). . .
Datin, K Dewarf, LE.; Guinan, EF.; Carton, JM. (January 2009). "FUSE Observations of alpha Centauri B". American Astronomical Society () 213: 200. :.
Nordstr?m, B.; Andersen, J.; Holmberg, J.; Pont, F.; J?rgensen, B. R.; Olsen, E. H.; Udry, S.; Mowlavi, N. et al. (2004). "The Geneva-Copenhagen survey of the Solar neighbourhood. Ages, metallicities, and kinematic properties of ~14000 F and G dwarfs".
418 (3): 989–1019. :. :. :.
, database entry, The Geneva-Copenhagen Survey of Solar neighbourhood, J. Holmberg et al., 2007,
ID . Accessed on line 19 November 2008
S?derhjelm, Staffan (1999). . Visual binary orbits and masses post Hipparcos.
Kervella, P Thevenin, Frederic (March 15, 2003). . .
from the original on 16 June 2008.
Gilli G.; Israelian G.; Ecuvillon A.; Santos NC.; Mayor M. (2006). "Abundances of Refractory Elements in the Atmospheres of Stars with Extrasolar Planets".
449 (2): 723–36. :. :. :. libcode 2005astro.ph.12219G.
Bazot, M. et al. (2007). "Asteroseismology of α Centauri A. Evidence of rotational splitting".
470 (1): 295–302. :. :. :.
Pourbaix, D. et al. (2002). "Constraining the difference in convective blueshift between the components of alpha Centauri with precise radial velocities".
386 (1): 280–85. :. :. :.
, Our Local Galactic Neighborhood, NASA
, Into the Interstellar Void, Centauri Dreams
Wall, Mike (). . . TechMediaNetwork.
Dumusque, X.; Pepe, F.; Lovis, C.; Ségransan, D.; Sahlmann, J.; Benz, W.; Bouchy, F.; ; ; Santos, N.;
490 (7423): 207–11. :. :.  .
Eric Hand, Nature, October 16, 2012. Accessed October 16, 2012.
Hatzes, Artie P. (May 21, 2013). .
770: 133. :. :. : 2013.
Overbye, Dennis. .
Burnham, Robert (1978). Burnham's Celestial Handbook. . p. 549.  .
Mason, B.D.; Wycoff, G.L. I. Hartkopf, W.I. (2008). . .
. Australia Telescope, Outreach and Education. Commonwealth Scientific and Industrial Research Organisation. December 21, 2004.
from the original on 12 November 2007.
Guinan, E.; Messina, S. (1995). "IAU Circular 6259, Alpha Centauri B". .
Robrade, J.; Schmitt, J. H. M. M.; Favata, F. (2005). "X-rays from α Centauri – The darkening of the solar twin".
442 (1): 315–321. :. :. :.
. SIMBAD. . — some of the data is located under "Measurements".
Kervella, P Thevenin, Frederic (). . ESO.
from the original on 7 June 2007.
Heintz, W. D. (1978). Double Stars. . p. 19.  .
Worley, C.E.; Douglass, G.G. (1996). . .
E. E. M L. A. Hillenbrand (2008). "Improved Age Estimation for Solar-Type Dwarfs Using Activity-Rotation Diagnostics". Astrophysical Journal 687 (2): . :. :. :.
Thévenin, F.; Provost, J.; Morel, P.; Berthomieu, G.; Bouchy, F.; Carrier, F. (2002). "Asteroseismology and calibration of alpha Cen binary system". Astronomy & Astrophysics 392: L9. :. :. :.
Bazot, M.; Bourguignon, S.; Christensen-Dalsgaard, J. (2012). "A Bayesian approach to the modelling of alpha Cen A". MNRAS 427: . :. :. :.
Miglio, A.; Montalbán, J. (2005). "Constraining fundamental stellar parameters using seismology. Application to α Centauri AB". Astronomy & Astrophysics 441: 615–629. :. :. :.
Thoul, A.; Scuflaire, R.; Noels, A.; Vatovez, B.; Briquet, M.; Dupret, M.-A.; Montalban, J. (2003). "A New Seismic Analysis of Alpha Centauri". Astronomy & Astrophysics 402: 293–297. :. :. :.
Eggenberger, P.; Charbonnel, C.; Talon, S.; Meynet, G.; Maeder, A.; Carrier, F.; Bourban, G. (2004). "Analysis of α Centauri AB including seismic constraints". Astronomy & Astrophysics 417: 235–246. :. :. :.
Van Zyl, Johannes Ebenhaezer (1996). Unveiling the Universe: An Introduction to Astronomy. Springer.  .
Hartung, E.J.; Frew, David Malin, David (1994). "Astronomical Objects for Southern Telescopes". .
Norton, A.P., Ed. I. Ridpath (1986). Norton's 0;:Star Atlas and Reference Handbook. . pp. 39–40.
Mitton, Jacquelin (1993). The Penguin Dictionary of Astronomy. . p. 148.
This is calculated for a fixed latitude by knowing the star's
(δ) using the formulae (90°+ δ). Alpha Centauri's declination is -60° 50′, so the latitude where the star is circumpolar will be south of -29° 10′S or 29°. Similarly, the place where Alpha Centauri never rises for northern observers is north of the latitude (90°+ δ) N or +29°N.
James, Andrew. . Sydney, New South Wales: Southern Astronomical Delights.
Matthews, R.A.J.; Gilmore, Gerard (1993). "Is Proxima really in orbit about α Cen A/B?".
261: L5. :. :.
Page, A.A. (1982). "Mount Tamborine Observatory". International Amateur-Professional Photoelectric Photometry Communication 10: 26. :.
Knobel, p. 416.
Kameswara Rao, R. (1984). "Father J. Richaud and early telescope observations in India".
Herschel, J.F.W. (1847). Results of Astronomical Observations made during the years ,7,8 at the Cape of Good H being the completion of a telescopic survey of the whole surface of the visible heavens, commenced in 1825. Smith, Elder and Co, London.
Kamper, K.W.; Wesselink, A. J. (1978). "Alpha and Proxima Centauri".
83: 1653. :. :.
, "The Binary Stars", Dover, 1961, pp. 236–237.
Hartkopf, W.; Mason, D. M. (2008). . .
Pannekoek, A., "A Short History of Astronomy", Dover, 1989, pp. 345–6
Boffin, Henri M.J. et al. ().
(PDF). Astronomy and Astrophysics 561: L4. :. :. :.
(PDF). ESA.
from the original on 6 August 2008.
(PDF). ESA.
Henderson, H. (1839). "On the parallax of α Centauri".
4 (19): 168–169. :. :.
Woolley R.; Epps E. A.; Penston M. J.; Pocock S. B. (1970). . Catalogue of stars within 25 parsecs of the Sun.
Gliese, W. and Jahreiss, H. (1991). . Preliminary Version of the Third Catalogue of Nearby Stars.
Van Altena W. F., Lee J. T., Hoffleit E. D. (1995). . The General Catalogue of Trigonometric Stellar Parallaxes (Fourth ed.).
Perryman et al. (1997). . The Hipparcos and Tycho Catalogues.
Perryman et al. (1997). . The Hipparcos and Tycho Catalogues.
Perryman et al. (1997). . The Hipparcos and Tycho Catalogues.
Perryman et al. (1997). . The Hipparcos and Tycho Catalogues.
van Leeuwen F. (2007). . Validation of the new Hipparcos reduction.
van Leeuwen F. (2007). . Validation of the new Hipparcos reduction.
. THE ONE HUNDRED NEAREST STAR SYSTEMS brought to you by RECONS (Research Consortium On Nearby Stars). 2012.
, "The Binary Stars", Dover, 1961, p. 236.
Kim, Y-C. J. (1999). "Standard Stellar M alpha Cen A and B".
32: 119. :.
Andrew James (). . .
, "The Binary Stars", Dover, 1961, p. 235.
Anosova, J; Orlov, V. V.; Pavlova, N. A. (1994).
292: 115. :.
Matthews, R.A.J. (1994). "The Close Approach of Stars in the Solar Neighbourhood".
35: 1–8. :.
Wetheimer, J.G.; Gregory Laughlin (2008). "Are Proxima and Alpha Centauri Gravitationally Bound?". The Astronomical Journal 132 (5): . :. :. :.
Ségransan, D.; Kervella, P.; Forveille, T.; Queloz, D. (2003). "First radius measurements of very low mass stars with the VLTI".
397 (3): L5–L8. :. :. :.
Clavin, W Harrington, J.D. (25 April 2014). . .
from the original on .
ESA: Hipparcos Site. .
Aristotle. .
Berry, A., "A History of Astronomy", Dover, 1989, pp. 357–358
Pannekoek, A., "A Short History of Astronomy", Dover, 1989
Holberg, JB (2007). Sirius: Brightest Diamond in the Night Sky. . pp. 41–42.  .
Tung, Brian. . The Astronomy Corner: Reference (2006).
, "The Crime of Claudius Ptolemy", T. Baltimore: Johns Hopkins University Press, (1977)
Pannekoek, A., "A Short History of Astronomy", Dover, 1989, p. 157
Grasshoff, G. (1990). The History of Ptolemy's Star Catalogue. . pp. 319–394.  .
Astronomical Society of South Africa. .
Pannekoek, A., "A Short History of Astronomy", Dover, 1989, p. 333
Maclear, M. (1851). "Determination of Parallax of α1and α2 Centauri".
32 (16): 243–244. :. :.
N.L., de La Caillé; Raven-Hart, R. (trans.& ed.) (1976). Travels at the Cape, : an annotated translation of Journal historique du voyage fait au Cap de Bonne-Espérance. Cape Town.  .
Proper motions are expressed in smaller angular units than , being measured in milli-arcsec (mas.) or one-thousandth of an arcsec. A negative value for proper motion in RA indicates the sky motion is east to west, in declination north to south.
van den Bos, W. H. (1926). "A Table of Orbits of Visual Binary Stars (aka. First Orbit Catalogue of Binary Stars)".
3: 149. :.
van den Bos, W. H. (1926). "Table of Visual Binary Stars".
C θ - θo = μα × sin α × (t - to ), α = right ascension (in degrees), μα is the common
(cpm.) expressed in degrees, and θ and θo are the current position angle and calculated position angle at the different epochs.
, April 1998 (p60), based on computations from
Quintana, E. V.; Lissauer, J. J.; Chambers, J. E.; Duncan, M. J.; (2002). "Terrestrial Planet Formation in the Alpha Centauri System". . 2, part 1 (2): 982–996. :. :.
jobs. . . : 2012.
Overbye, Dennis (October 17, 2012). . New York Times 2012.
Palmer, Jason (October 17, 2012). . BBC 2012.
F B D A U B G L N Mayor, M.; Pepe, F.; Queloz, D.; Santos, N. C.; Segransan, D.; Almenara, J. M.; Deeg, H.; Rabus, M. (2011). "Alpha Centauri". : [].
Demory, Brice-O Ehrenreich, D Queloz, D Seager, S Gilliland, R Chaplin, William J.; Proffitt, C Gillon, M Guenther, Maximilian N.; Benneke, B Dumusque, X Lovis, C Pepe, F Segransan, D Triaud, A Udry, Stephane (25 March 2015). "Hubble Space Telescope search for the transit of the Earth-mass exoplanet Alpha Centauri Bb". v1. : [].
from the original on 21 April .
Stephens, Tim (7 March 2008). . News & Events. .
from the original on 17 April .
Thebault, P., Marzazi, F., Scholl, H.; M Scholl (2009). "Planet formation in the habitable zone of alpha centauri B".
393: L21–L25. :. :. :.
Javiera M. Guedes, Eugenio J. Rivera, Erica Davis, Gregory Laughlin, Elisa V. Quintana, Debra A. F R D L Q Fischer (2008). "Formation and Detectability of Terrestrial Planets Around Alpha Centauri B".
679 (2): . :. :. :.
Ian O'Neill, Ian (8 July 2008). . .
Javiera Guedes,
see Lissauer and Quintana in references below
M. Barbieri, F. Marzari, H. S M Scholl (2002). "Formation of terrestrial planets in close binary systems: The case of α Centauri A".
396 (1): 219 – 224. :. :. :.
P.A. Wiegert and M.J. Holman (1997). "The stability of planets in the Alpha Centauri system".
113: ;– 1450. :. :. :.
Lissauer, J. J., E. V. Quintana, J. E. Chambers, M. J. Duncan, and F. C. Adams. (2004). "Terrestrial Planet Formation in Binary Star Systems".
(Serie de Conferencias) 22: 99–103. :.
Quintana, E. V.; Lissauer, J. J.; (2007). "Terrestrial Planet Formation in Binary Star Systems". .
Croswell, K. (1991). "Does Alpha Centauri Have Intelligent Life?".
19: 28–37.
. Centauri-dreams.org. .
from the original on 14 March 2008.
"", (), NASA, Stars and Galaxies, , 18 October 2006. Retrieved 24 April 2007.
Mullen, Leslie (2 June 2011). . Astrobiology Magazine.
from the original on 4 June 2011.
The coordinates of the Sun would be diametrically opposite Alpha Centauri AB, at α=02h 39m 36.4951s, δ=+60° 50′ 02.308″
C using in solar terms: 1.1 M☉ and 0.92 M☉, luminosities 1.57 and 0.51 L*/L☉, Sun magnitude -26.73(v), 11.2 to 35.6 AU The minimum luminosity adds planet's orbital radius to A–B distance (max) (conjunction). Max. luminosity subtracts the planet's orbital radius to A–B distance (min) (opposition).
Kunitzsch P., & Smart, T., A Dictionary of Modern star Names: A Short Guide to 254 Star Names and Their Derivations, Cambride, Sky Pub. Corp., 2006, p. 27
Bailey, F., "The Catalogues of Ptolemy, Ulugh Beigh, Tycho Brahe, Halley, and Hevelius", Memoirs of Royal Astronomical Society, vol. XIII, London, 1843.
Davis Jr., G. A., Popular Astronomy, Vol. LII, No. 3, Oct. 1944, p. 16.
Burritt, E. H., , Designed to Illustrate the Geography of the Heavens, (New Edition), New York, F. J. Huntington and Co., 1835, pl. VII.
(Chinese) [ AEEA (Activities of Exhibition and Education in Astronomy) 天文教育資訊網 2006 年 6 月 27 日]
Hamacher, Duane W.; Frew, David J. (2010). "An Aboriginal Australian Record of the Great Eruption of Eta Carinae". Journal of Astronomical History & Heritage 13 (3): 220–34.
Stanbridge, WM (1857). "On the Astronomy and Mythology of the Aboriginies of Victoria". Transactions Philosophical Institute Victoria 2: 137–140.
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