Alpha Centauri
Alpha Centauri AB (left) forms a triple star system with Proxima Centauri, circled in red. The bright star system to the right is Beta Centauri. | ||
Observation data J2000.0
| ||
---|---|---|
Constellation | Centaurus | |
Alpha Centauri A | ||
Right ascension | 14h 39m 36.49400s[1] | |
Declination | −60° 50′ 02.3737″ | |
Apparent magnitude (V) | +0.01[2] | |
Alpha Centauri B | ||
Right ascension | 14h 39m 35.06311s[1] | |
Declination | −60° 50′ 15.0992″ | |
Apparent magnitude (V) | +1.33[2] | |
Characteristics | ||
A | ||
Spectral type | G2V[3] | |
U−B color index | +0.24[citation needed] | |
B−V color index | +0.71[2] | |
B | ||
Spectral type | K1V[3] | |
U−B color index | +0.68[citation needed] | |
B−V color index | +0.88[2] | |
Absolute magnitude (MV) | 5.71[6] | |
Argument of periastron (ω)(secondary) | 231.519±0.027° | |
Details | ||
Alpha Centauri A | ||
Gyr | ||
HIP 71681 | ||
Database references | ||
Exoplanet Archive | data | |
ARICNS | data |
Alpha Centauri (α Centauri, Alpha Cen, or α Cen) is a triple
Alpha Centauri A and B are
Alpha Centauri A has 1.1 times the
Alpha Centauri C, or Proxima Centauri, is a small faint red dwarf (Class M). Though not visible to the naked eye, Proxima Centauri is the closest star to the Sun at a distance of 4.24 ly (1.30 pc), slightly closer than Alpha Centauri AB. Currently, the distance between Proxima Centauri and Alpha Centauri AB is about 13,000 AU (0.21 ly),[16] equivalent to about 430 times the radius of Neptune's orbit.
Proxima Centauri has two confirmed planets: Proxima b, an Earth-sized planet in the habitable zone discovered in 2016, and Proxima d, a candidate sub-Earth which orbits very closely to the star, announced in 2022.[17] The existence of Proxima c, a mini-Neptune 1.5 AU away discovered in 2019, is controversial.[18] Alpha Centauri A may have a Neptune-sized planet in the habitable zone, though it is not yet known with certainty to be planetary in nature and could be an artifact of the discovery mechanism.[19] Alpha Centauri B has no known planets: planet Bb, purportedly discovered in 2012, was later disproven,[20] and no other planet has yet been confirmed.
Etymology and nomenclature
α Centauri (Latinised to Alpha Centauri) is the system's designation given by Johann Bayer in 1603. It belongs to the constellation Centaurus, named after the half human, half horse creature in Greek mythology. Hercules accidentally wounded the centaur and placed him in the sky after his death. Alpha Centauri marks the right front hoof of the Centaur.[21] The common name Rigil Kentaurus is a Latinisation of the Arabic translation رجل القنطورس Rijl al-Qinṭūrus, meaning 'the Foot of the Centaur'.[22][23] Qinṭūrus is the Arabic transliteration of the Greek Κένταυρος (Centaurus).[24] The name is frequently abbreviated to Rigil Kent or even Rigil, though the latter name is better known for Rigel (Beta Orionis).[25]
An alternative name found in European sources, Toliman, is an approximation of the Arabic الظليمان aẓ-Ẓalīmān (in older transcription, aṭ-Ṭhalīmān), meaning 'the (two male) Ostriches', an appellation Zakariya al-Qazwini had applied to the pair of stars Lambda and Mu Sagittarii; it was often not clear on old star maps which name was intended to go with which star (or stars), and the referents changed over time.[26]
A third name that has been used is Bungula (/ˈbʌŋɡjuːlə/). Its origin is not known, but it may have been coined from the Greek letter beta (β) and Latin ungula 'hoof', originally for Beta Centauri (the other hoof).[25]
Alpha Centauri C was discovered in 1915 by
In 2016, the
Observation
To the naked eye, Alpha Centauri AB appears to be a single star, the
South of about 29° South latitude, Alpha Centauri is circumpolar and never sets below the horizon.[note 2] North of about 29° N latitude, Alpha Centauri never rises. Alpha Centauri lies close to the southern horizon when viewed from the 29° North latitude to the equator (close to Hermosillo and Chihuahua City in Mexico; Galveston, Texas; Ocala, Florida; and Lanzarote, the Canary Islands of Spain), but only for a short time around its culmination.[38] The star culminates each year at local midnight on 24 April and at local 9 p.m. on 8 June.[38][40]
As seen from Earth, Proxima Centauri is 2.2° southwest from Alpha Centauri AB; this distance is about four times the
Alpha Centauri may be inside the
Observational history
Alpha Centauri is listed in the 2nd-century
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 [Canopus]. The second [Achernar] is in the end of Eridanus. The third [Alpha Centauri] is in the right foote of the Centaure.[48]
The binary nature of Alpha Centauri AB was recognized in December 1689 by Jean Richaud, while observing a passing comet from his station in Puducherry. Alpha Centauri was only the second binary star to be discovered, preceded by Acrux.[49]
The large proper motion of Alpha Centauri AB was discovered by
Later,
By 1926, William Stephen Finsen calculated the approximate orbit elements close to those now accepted for this system.[54] All future positions are now sufficiently accurate for visual observers to determine the relative places of the stars from a binary star ephemeris.[55] Others, like D. Pourbaix (2002), have regularly refined the precision of new published orbital elements.[15]
Robert T. A. Innes discovered Proxima Centauri in 1915 by blinking photographic plates taken at different times during a proper motion survey. These showed large proper motion and parallax similar in both size and direction to those of Alpha Centauri AB, which suggested that Proxima Centauri is part of the Alpha Centauri system and slightly closer to Earth than Alpha Centauri AB. As such, Innes concluded that Proxima Centauri was the closest star to Earth yet discovered.
Kinematics
All components of Alpha Centauri display significant
In the 1830s,
Calculated proper motion of the centre of mass for Alpha Centauri AB is about 3620 mas/y (milliarcseconds per year) toward the west and 694 mas/y toward the north, giving an overall motion of 3686 mas/y in a direction 11° north of west.
Since Alpha Centauri AB is almost exactly in the plane of the Milky Way as viewed from Earth, many stars appear behind it. In early May 2028, Alpha Centauri A will pass between the Earth and a distant red star, when there is a 45% probability that an Einstein ring will be observed. Other conjunctions will also occur in the coming decades, allowing accurate measurement of proper motions and possibly giving information on planets.[64]
Predicted future changes
Based on the system's common proper motion and radial velocities, Alpha Centauri will continue to change its position in the sky significantly and will gradually brighten. For example, in about 6,200 AD, α Centauri's true motion will cause an extremely rare first-magnitude stellar conjunction with Beta Centauri, forming a brilliant optical double star in the southern sky.[66] It will then pass just north of the Southern Cross or Crux, before moving northwest and up towards the present celestial equator and away from the galactic plane. By about 26,700 AD, in the present-day constellation of Hydra, Alpha Centauri will reach perihelion at 0.90 pc or 2.9 ly away,[67] though later calculations suggest that this will occur in 27,000 AD.[68] At nearest approach, Alpha Centauri will attain a maximum apparent magnitude of −0.86, comparable to present-day magnitude of Canopus, but it will still not surpass that of Sirius, which will brighten incrementally over the next 60,000 years, and will continue to be the brightest star as seen from Earth (other than the Sun) for the next 210,000 years.[69]
Stellar system
Alpha Centauri is a triple star system, with its two main stars, Alpha Centauri A and Alpha Centauri B, together comprising a binary component. The AB designation, or older A×B, denotes the mass centre of a main binary system relative to companion star(s) in a multiple star system.[70] AB-C refers to the component of Proxima Centauri in relation to the central binary, being the distance between the centre of mass and the outlying companion. Because the distance between Proxima (C) and either of Alpha Centauri A or B is similar, the AB binary system is sometimes treated as a single gravitational object.[71]
Orbital properties
The A and B components of Alpha Centauri have an orbital period of 79.762 years.[5] Their orbit is moderately eccentric, as it has an eccentricity of almost 0.52;[5] their closest approach or periastron is 11.2 AU (1.68×10 9 km), or about the distance between the Sun and Saturn; and their furthest separation or apastron is 35.6 AU (5.33×10 9 km), about the distance between the Sun and Pluto.[15] The most recent periastron was in August 1955 and the next will occur in May 2035; the most recent apastron was in May 1995 and will next occur in 2075.
Viewed from Earth, the apparent orbit of A and B means that their separation and position angle (PA) are in continuous change throughout their projected orbit. Observed stellar positions in 2019 are separated by 4.92 arcsec through the PA of 337.1°, increasing to 5.49 arcsec through 345.3° in 2020.[15] The closest recent approach was in February 2016, at 4.0 arcsec through the PA of 300°.[15][73] The observed maximum separation of these stars is about 22 arcsec, while the minimum distance is 1.7 arcsec.[54] The widest separation occurred during February 1976, and the next will be in January 2056.[15]
Alpha Centauri C is about 13,000 AU (0.21 ly; 1.9×10 12 km) from Alpha Centauri AB, equivalent to about 5% of the distance between Alpha Centauri AB and the Sun.[16][41][53] Until 2017, measurements of its small speed and its trajectory were of too little accuracy and duration in years to determine whether it is bound to Alpha Centauri AB or unrelated.
Radial velocity measurements made in 2017 were precise enough to show that Proxima Centauri and Alpha Centauri AB are gravitationally bound.[16] The orbital period of Proxima Centauri is approximately 511000+41000
−30000 years, with an eccentricity of 0.5, much more eccentric than Mercury's. Proxima Centauri comes within 4100+700
−600 AU of AB at periastron, and its apastron occurs at 12300+200
−100 AU.[5]
Physical properties
From the orbital elements, the total mass of Alpha Centauri AB is about 2.0 M☉[note 4] – or twice that of the Sun.[54] The average individual stellar masses are about 1.08 M☉ and 0.91 M☉, respectively,[5] though slightly different masses have also been quoted in recent years, such as 1.14 M☉ and 0.92 M☉,[81] totalling 2.06 M☉. Alpha Centauri A and B have absolute magnitudes of +4.38 and +5.71, respectively.
Alpha Centauri AB System
Alpha Centauri A
Alpha Centauri A, also known as Rigil Kentaurus, is the principal member, or primary, of the binary system. It is a solar-like
The type of
Alpha Centauri B
Alpha Centauri B, also known as Toliman, is the secondary star of the binary system. It is a main-sequence star of spectral type K1-V, making it more an orange colour than Alpha Centauri A;[82] it has around 90% of the mass of the Sun and a 14% smaller diameter. Although it has a lower luminosity than A, Alpha Centauri B emits more energy in the X-ray band.[85] Its light curve varies on a short time scale, and there has been at least one observed flare.[85] It is more magnetically active than Alpha Centauri A, showing a cycle of 8.2±0.2 yr compared to 11 years for the Sun, and has about half the minimum-to-peak variation in coronal luminosity of the Sun.[84] Alpha Centauri B has an apparent magnitude of +1.35, slightly dimmer than Mimosa.[33]
Alpha Centauri C (Proxima Centauri)
Alpha Centauri C, better known as Proxima Centauri, is a small main-sequence red dwarf of spectral class M6-Ve. It has an absolute magnitude of +15.60, over 20,000 times fainter than the Sun. Its mass is calculated to be 0.1221 M☉.[86] It is the closest star to the Sun but is too faint to be visible to the naked eye.[87]
Planetary system
The Alpha Centauri system as a whole has two confirmed planets, both of them around Proxima Centauri. While other planets have been claimed to exist around all of the stars, none of the discoveries have been confirmed.
Planets of Proxima Centauri
Proxima Centauri b is a terrestrial planet discovered in 2016 by astronomers at the
The discovery of Proxima Centauri c was formally published in 2020 and could be a super-Earth or mini-Neptune.[90][91] It has a mass of roughly 7 ME and orbits about 1.49 AU from Proxima Centauri with a period of 1,928 days (5.28 yr).[92] In June 2020, a possible direct imaging detection of the planet hinted at the presence of a large ring system.[93] However, a 2022 study disputed the existence of this planet.[18]
A 2020 paper refining Proxima b's mass excludes the presence of extra companions with masses above 0.6 ME at periods shorter than 50 days, but the authors detected a radial-velocity curve with a periodicity of 5.15 days, suggesting the presence of a planet with a mass of about 0.29 ME.[89] This planet, Proxima Centauri d, was confirmed in 2022.[17][18]
Planets of Alpha Centauri A
Companion (in order from star) |
Mass | Semimajor axis (AU) |
Orbital period (days) |
Eccentricity | Inclination | Radius |
---|---|---|---|---|---|---|
b (unconfirmed) | ~9–35[note 5] M🜨 | 1.1 | ~360 | — | ~65 ± 25° | ~3.3–7 R🜨 |
In 2021, a candidate planet named Candidate 1 (abbreviated as C1) was detected around Alpha Centauri A, thought to orbit at approximately 1.1 AU with a period of about one year, and to have a mass between that of Neptune and one-half that of Saturn, though it may be a dust disk or an artifact. The possibility of C1 being a background star has been ruled out.[94][19] If this candidate is confirmed, the temporary name C1 will most likely be replaced with the scientific designation Alpha Centauri Ab in accordance with current naming conventions.[95]
GO Cycle 1 observations are planned for the James Webb Space Telescope (JWST) to search for planets around Alpha Centauri A, as well as observations of Epsilon Muscae.[96] The coronographic observations, which occurred on July 26 and 27, 2023, were failures, though there are follow-up observations in March 2024.[97] Pre-launch estimates predicted that JWST will be able to find planets with a radius of 5 R🜨 at 1–3 au. Multiple observations every 3–6 months could push the limit down to 3 R🜨.[98] Post-processing techniques could push the limit down to 0.5 to 0.7 R🜨.[96] Post-launch estimates based on observations of HIP 65426 b find that JWST will be able to find planets even closer to Alpha Centauri A and could find a 5 R🜨 planet at 0.5 to 2.5 au.[99] Candidate 1 has an estimated radius between 3.3 and 11 R🜨[19] and orbits at 1.1 au. It is therefore likely within the reach of JWST observations.
Planets of Alpha Centauri B
In 2012, a planet around Alpha Centauri B was reported, Alpha Centauri Bb, but in 2015 a new analysis concluded that that report was an artifact of the datum analysis.[100][101][20]
A possible transit-like event was observed in 2013, which could be associated with a separate planet. The transit event could correspond to a planetary body with a radius around 0.92 R🜨. 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 of the likely orbits is 12.4 days. Its orbit would likely have an eccentricity of 0.24 or less.[102] It could have lakes of molten lava and would be far too close to Alpha Centauri B to harbour life.[103] If confirmed, this planet might be called Alpha Centauri Bc. However, the name has not been used in the literature, as it is not a claimed discovery. As of 2023[update], it appears that no further transit-like events have been observed.
Hypothetical planets
Additional planets may exist in the Alpha Centauri system, either orbiting Alpha Centauri A or Alpha Centauri B individually, or in large orbits around Alpha Centauri AB. Because both stars are fairly similar to the Sun (for example, in age and metallicity), astronomers have been especially interested in making detailed searches for planets in the Alpha Centauri system. Several established planet-hunting teams have used various radial velocity or star transit methods in their searches around these two bright stars.[104] All the observational studies have so far failed to find evidence for brown dwarfs or gas giants.[104][105]
In 2009, computer simulations 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 the Alpha Centauri pair 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
Radial velocity measurements of Alpha Centauri B made with the
Current estimates place the probability of finding an Earth-like planet around Alpha Centauri at roughly 75%.[110] The observational thresholds for planet detection in the habitable zones by the radial velocity method are currently (2017) estimated to be about 50 ME for Alpha Centauri A, 8 ME for Alpha Centauri B, and 0.5 ME for Proxima Centauri.[111]
Early computer-generated models of planetary formation predicted the existence of
In the Solar System, it was once thought that Jupiter and Saturn were probably crucial in perturbing comets into the inner Solar System, providing the inner planets with a source of water and various other ices.[115] However, since isotope measurements of the deuterium to hydrogen (D/H) ratio in comets Halley, Hyakutake, Hale–Bopp, 2002T7, and Tuttle yield values approximately twice that of Earth's oceanic water, more recent models and research predict that less than 10% of Earth's water was supplied from comets. In the Alpha Centauri system, Proxima Centauri may have influenced the planetary disk as the Alpha Centauri system was forming, enriching the area around Alpha Centauri with volatile materials.[116] This would be discounted if, for example, Alpha Centauri B happened to have gas giants orbiting Alpha Centauri A (or vice versa), or if Alpha Centauri A and B themselves were able to perturb comets into each other's inner systems as Jupiter and Saturn presumably have done in the Solar System.[115] Such icy bodies probably also reside in Oort clouds 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 star-wards.[115] Such ideas also apply to the close approach of Alpha Centauri or other stars to the Solar System, when, in the distant future, the Oort Cloud might be disrupted enough to increase the number of active comets.[67]
To be in the habitable zone, a planet around Alpha Centauri A would have an orbital radius of between about 1.2 and 2.1 AU so as to have similar planetary temperatures and conditions for liquid water to exist.[117] For the slightly less luminous and cooler Alpha Centauri B, the habitable zone is between about 0.7 and 1.2 AU.[117]
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 NASA's Space Interferometry Mission (S.I.M.). Detecting planets as small as three Earth-masses or smaller within two AU of a "Tier-1" target would have been possible with this new instrument.[118] The S.I.M. mission, however, was cancelled due to financial issues in 2010.[119]
Circumstellar discs
Based on observations between 2007 and 2012, a study found a slight excess of emissions in the 24-μm (mid/far-infrared) band surrounding α Centauri AB, which may be interpreted as evidence for a sparse
View from this system
This section needs additional citations for verification. (March 2023) |
The sky from Alpha Centauri AB would appear much as it does from the Earth, except that Centaurus's brightest star, being Alpha Centauri AB itself, would be absent from the constellation. The Sun would appear as a white star of apparent magnitude +0.5,[121] roughly the same as the average brightness of Betelgeuse from Earth. It would be at the antipodal point of Alpha Centauri AB's current right ascension and declination, at 02h 39m 36s +60° 50′ 02.308″ (2000), in eastern Cassiopeia, easily outshining all the rest of the stars in the constellation. With the placement of the Sun east of the magnitude 3.4 star Epsilon Cassiopeiae, nearly in front of the Heart Nebula, the "W" line of stars of Cassiopeia would have a "/W" shape.[122]
The Winter Triangle would not look equilateral, but very thin and long, with Procyon outshining Pollux in the middle of Gemini, and Sirius lying less than a degree from Betelgeuse in Orion. With a magnitude of −1.2, Sirius would be a little fainter than from Earth but still the brightest star in the night sky. Both Vega and Altair would be shifted northwestward relative to Deneb, giving the Summer Triangle a more equilateral appearance.[citation needed]
A planet around either α Centauri A or B would see the other star as a very bright secondary. For example, an Earth-like planet at 1.25 AU from α Cen A (with a revolution period of 1.34 years) would get Sun-like illumination from its primary, and α Cen B would appear 5.7 to 8.6 magnitudes dimmer (−21.0 to −18.2), 190 to 2,700 times dimmer than α Cen A but still 150 to 2,100 times brighter than the full Moon. Conversely, an Earth-like planet at 0.71 AU from α Cen B (with a revolution period of 0.63 years) would get nearly Sun-like illumination from its primary, and α Cen A would appear 4.6 to 7.3 magnitudes dimmer (−22.1 to −19.4), 70 to 840 times dimmer than α Cen B but still 470 to 5,700 times brighter than the full Moon.
Proxima Centauri would appear dim as one of many stars.[123]
Other names
In modern literature, colloquial alternative names of Alpha Centauri include Rigil Kent[124] (also Rigel Kent and variants;[note 7] /ˈraɪdʒəl ˈkɛnt/)[22][125] and Toliman[126] (the latter of which became the proper name of Alpha Centauri B on 10 August 2018 by approval of the International Astronomical Union).
Rigil Kent is short for Rigil Kentaurus,
The name Toliman originates with Jacobus Golius' 1669 edition of Al-Farghani's Compendium. Tolimân is Golius' latinisation of the Arabic name الظلمان al-Ẓulmān "the ostriches", the name of an asterism of which Alpha Centauri formed the main star.[128][129][130]
During the 19th century, the northern amateur popularist Elijah H. Burritt used the now-obscure name Bungula,[131] possibly coined from "β" and the Latin ungula ("hoof").[22]
Together, Alpha and Beta Centauri form the "Southern Pointers" or "The Pointers", as they point towards the Southern Cross, the asterism of the constellation of Crux.[66]
In
To the Indigenous
Future exploration
Alpha Centauri is a first target for crewed or robotic
NASA released a mission concept in 2017 that would send a spacecraft to Alpha Centauri in 2069, scheduled to coincide with the 100th anniversary of the first crewed lunar landing in 1969, Apollo 11. Even at speed 10% of the speed of light (about 108 million km/h), which NASA experts say may be possible, it would take a spacecraft 44 years to reach the constellation, by the year 2113, and would take another 4 years for a signal, by the year 2117 to reach Earth. The concept received no further funding or development.[141][142]
Historical distance estimates
Source | Year | Subject | Parallax ( mas ) |
Distance | References | ||
---|---|---|---|---|---|---|---|
parsecs | light-years | petametres
| |||||
H. Henderson | 1839 | AB | 1160±110 | 0.86+0.09 −0.07 |
2.81 ± 0.53 | 26.6+2.8 −2.3 |
[59] |
T. Henderson | 1842 | AB | 912.8±64 | 1.10 ± 0.15 | 3.57 ± 0.5 | 33.8+2.5 −2.2 |
[143] |
Maclear | 1851 | AB | 918.7±34 | 1.09±0.04 | 3.55+0.14 −0.13 |
32.4 ± 2.5 | [144] |
Moesta | 1868 | AB | 880±68 | 1.14+0.10 −0.08 |
3.71+0.31 −0.27 |
35.1+2.9 −2.5 |
[145] |
Gill & Elkin | 1885 | AB | 750±10 | 1.333±0.018 | 4.35±0.06 | 41.1+0.6 −0.5 |
[146] |
Roberts | 1895 | AB | 710±50 | 1.32 ± 0.2 | 4.29 ± 0.65 | 43.5+3.3 −2.9 |
[147] |
Woolley et al. | 1970 | AB | 743±7 | 1.346±0.013 | 4.39±0.04 | 41.5±0.4 | [148] |
Gliese & Jahreiß | 1991 | AB | 749.0±4.7 | 1.335±0.008 | 4.355±0.027 | 41.20±0.26 | [149] |
van Altena et al. | 1995 | AB | 749.9±5.4 | 1.334±0.010 | 4.349+0.032 −0.031 |
41.15+0.30 −0.29 |
[150] |
Perryman et al. | 1997 | AB | 742.12±1.40 | 1.3475±0.0025 | 4.395±0.008 | 41.58±0.08 | [151][152][153][154] |
Söderhjelm | 1999 | AB | 747.1±1.2 | 1.3385+0.0022 −0.0021 |
4.366±0.007 | 41.30±0.07 | [155] |
van Leeuwen | 2007 | A | 754.81±4.11 | 1.325±0.007 | 4.321+0.024 −0.023 |
40.88±0.22 | [156] |
B | 796.92±25.90 | 1.25±0.04 | 4.09+0.14 −0.13 |
37.5 ± 2.5 | [157] | ||
RECONS TOP100 | 2012 | AB | 747.23±1.17[note 8] | 1.3383±0.0021 | 4.365±0.007 | 41.29±0.06 | [81] |
In culture
Alpha Centauri has been recognized and associated throughout history, particularly on the
In fiction
See also
- Alpha Centauri in fiction
- List of nearest stars and brown dwarfs
- Project Longshot
- Sagan Planet Walk
Notes
- ^ Proxima Centauri is gravitationally bound to the α Centauri system, but for practical and historical reasons it is described in detail in its own article.
- ^ This is calculated for a fixed latitude by knowing the star's declination (δ) using the formulae (90°+ δ). Alpha Centauri's declination is −60° 50′, so the observed latitude where the star is circumpolar will be south of −29° 10′ South or 29°. Similarly, the place where Alpha Centauri never rises for northern observers is north of the latitude (90°+ δ) N or +29° North.
- ^ Proper motions are expressed in smaller angular units than arcsec, being measured in milliarcsec (mas.) (thousandths of an arcsec). Negative values for proper motion in RA indicate the sky motion is from east to west, and in declination north to south.
- ^ , see formula
- ^ These mass limits are calculated from the observed radius of ~3.3–7 R🜨 applied to the equation quoted, and presumably used, to calculate the planet mass from the planet radius in the K. Wagner et al. 2021 paper – R ∝ M0.55 (although this radius-mass relationship is for low-mass planets and not for larger gas giants). Therefore 3.31.82 = 8.77 ME and 71.82 = 34.52 ME. The Msini ≥ 53 ME is for a planet at the outer edge of the conservative habitable zone, 2.1 AU, and so the upper mass limit is lower than that for the C1 planet at just 1.1 AU.
- ^ See Lissauer and Quintana in references below
- ^ Spellings include Rigjl Kentaurus, Hyde T., "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., "Crux Australis: o Cruzeiro do Sul" Archived 6 December 2013 at the Wayback Machine, Artigos: Planetario Movel Inflavel AsterDomus.
- ^ Weighted parallax based on parallaxes from van Altena et al. (1995) and Söderhjelm (1999)
References
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The first great science-fiction story in which Alpha Centauri played a major role may have been a 1944 tale by A. E. van Vogt. I read it in a much later anthology when I was a kid. The title of the tale—including the sound of that title—was what really filled me with admiration and has stuck with me ever since: "Far Centaurus." Although the name Proxima Centauri basically means "near Centaurus," the title of the story is appropriate because the tale tells of a first spaceship journey that would take many generations to complete—"'Tis for far Centaurus we sail!"
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Alpha Centauri (1997), in which terrorists plague the colony ship which is humankind's last hope
External links
- SIMBAD observational data
- Sixth Catalogue of Orbits of Visual Binary Stars U.S.N.O.
- The Imperial Star – Alpha Centauri
- Alpha Centauri – A Voyage to Alpha Centauri
- Immediate History of Alpha Centauri
- eSky: Alpha Centauri
Hypothetical planets or exploration
- Alpha Centauri System
- O Sistema Alpha Centauri (Portuguese) Archived 3 March 2016 at the Wayback Machine
- Alpha Centauri – Associação de Astronomia (Portuguese)
- Thompson, Andrea (7 March 2008). "Nearest Star System Might Harbor Earth Twin". Space.com. Archived from the original on 2 June 2008. Retrieved 18 November 2021.