130-522: Alpha Centauri ( α Centauri , α Cen , or Alpha Cen ) is a triple star system in the southern constellation of Centaurus . It consists of three stars: Rigil Kentaurus ( α Centauri A ), Toliman ( α Centauri B ), and Proxima Centauri ( α Centauri C ). Proxima Centauri is the closest star to the Sun at 4.2465 light-years (1.3020 pc ). α Centauri A and B are Sun-like stars ( class G and K , respectively) that together form
260-625: A B-V color index of −0.06. It contrasts strongly with reddish Betelgeuse. Culminating every year at midnight on 12 December, and at 9:00 pm on 24 January, Rigel is visible on winter evenings in the Northern Hemisphere and on summer evenings in the Southern Hemisphere . In the Southern Hemisphere, Rigel is the first bright star of Orion visible as the constellation rises. Correspondingly, it
390-408: A P Cygni profile after a star that shows this feature strongly in its spectrum. It is associated with mass loss where there is simultaneously emission from a dense wind close to the star and absorption from circumstellar material expanding away from the star. The unusual Hα line profile is observed to vary unpredictably. It is a normal absorption line around a third of the time. About a quarter of
520-401: 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. 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
650-401: A margin of error of about 9%. Rigel B, usually considered to be physically associated with Rigel and at the same distance, has a Gaia Data Release 3 parallax of 3.2352 ± 0.0553 mas , suggesting a distance around 1,000 light-years (310 parsecs). However, the measurements for this object may be unreliable. Indirect distance estimation methods have also been employed. For example, Rigel
780-412: A binary system, and in 1878, he resolved it into two components. This visual companion is designated as component C (Rigel C), with a measured separation from component B that varies from less than 0.1″ to around 0.3″ . In 2009, speckle interferometry showed the two almost identical components separated by 0.124″ , with visual magnitudes of 7.5 and 7.6, respectively. Their estimated orbital period
910-552: A brilliant optical double star in the southern sky. 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 CE , in the present-day constellation of Hydra , α Centauri will reach perihelion at 0.90 pc or 2.9 ly away, though later calculations suggest that this will occur in 27,000 AD. At its nearest approach, α Centauri will attain
1040-449: A challenging target for telescope apertures smaller than 15 cm (6 in). At Rigel's estimated distance, Rigel B's projected separation from Rigel A is over 2,200 astronomical units (AU). Since its discovery, there has been no sign of orbital motion, although both stars share a similar common proper motion . The pair would have an estimated orbital period of 24,000 years. Gaia Data Release 2 (DR2) contains
1170-411: A close binary with a distant companion, with the other star(s) previously in the system ejected into interstellar space at high velocities. This dynamic may explain the runaway stars that might have been ejected during a collision of two binary star groups or a multiple system. This event is credited with ejecting AE Aurigae , Mu Columbae and 53 Arietis at above 200 km·s and has been traced to
1300-597: A cutlass by the maiden Bįhi (Sirius). The Lacandon people of southern Mexico knew it as tunsel ("little woodpecker"). Rigel was known as Yerrerdet-kurrk to the Wotjobaluk koori of southeastern Australia, and held to be the mother-in-law of Totyerguil ( Altair ). The distance between them signified the taboo preventing a man from approaching his mother-in-law. The indigenous Boorong people of northwestern Victoria named Rigel as Collowgullouric Warepil . The Wardaman people of northern Australia know Rigel as
1430-709: A daughter of Rehua ( Antares ), the chief of all-stars. Its heliacal rising presages the appearance of Matariki (the Pleiades ) in the dawn sky, marking the Māori New Year in late May or early June. The Moriori people of the Chatham Islands , as well as some Maori groups in New Zealand, mark the start of their New Year with Rigel rather than the Pleiades. Puaka is a southern name variant used in
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#17327727003921560-411: A designation system, identifying the hierarchy within the system has the advantage that it makes identifying subsystems and computing their properties easier. However, it causes problems when new components are discovered at a level above or intermediate to the existing hierarchy. In this case, part of the hierarchy will shift inwards. Components which are found to be nonexistent, or are later reassigned to
1690-883: A diagram multiplex if there is a node with more than two children , i.e. if the decomposition of some subsystem involves two or more orbits with comparable size. Because, as we have already seen for triple stars, this may be unstable, multiple stars are expected to be simplex , meaning that at each level there are exactly two children . Evans calls the number of levels in the diagram its hierarchy . Higher hierarchies are also possible. Most of these higher hierarchies either are stable or suffer from internal perturbations . Others consider complex multiple stars will in time theoretically disintegrate into less complex multiple stars, like more common observed triples or quadruples are possible. Trapezia are usually very young, unstable systems. These are thought to form in stellar nurseries, and quickly fragment into stable multiple stars, which in
1820-548: A diameter of 25 million miles, or approximately 28.9 R ☉ , smaller than its neighbor Aldebaran . Due to their closeness to each other and ambiguity of the spectrum, little is known about the intrinsic properties of the members of the Rigel BC triple system. All three stars seem to be near equally hot B-type main-sequence stars that are three to four times as massive as the Sun. Stellar evolution models suggest
1950-540: A different subsystem, also cause problems. During the 24th General Assembly of the International Astronomical Union in 2000, the WMC scheme was endorsed and it was resolved by Commissions 5, 8, 26, 42, and 45 that it should be expanded into a usable uniform designation scheme. A sample of a catalog using the WMC scheme, covering half an hour of right ascension , was later prepared. The issue
2080-473: A direction 11° north of west. The motion of the centre of mass is about 6.1 arcmin each century, or 1.02 ° each millennium. The speed in the western direction is 23.0 km/s (14.3 mi/s) and in the northerly direction 4.4 km/s (2.7 mi/s). Using spectroscopy the mean radial velocity has been determined to be around 22.4 km/s (13.9 mi/s) towards the Solar System. This gives
2210-795: A dust disk or an artifact. The possibility of C1 being a background star has been ruled out. 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. 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 . The coronographic observations, which occurred on July 26 and 27, 2023, were failures, though there are follow-up observations in March 2024. Pre-launch estimates predicted that JWST will be able to find planets with
2340-521: A few hours to several days, but again no clear period. Rigel's color index varies slightly, but this is not significantly correlated with its brightness variations. From analysis of Hipparcos satellite photometry, Rigel is identified as belonging to the Alpha Cygni class of variable stars, defined as "non-radially pulsating supergiants of the Bep–AepIa spectral types". In those spectral types,
2470-584: A few minutes. Some amateur and professional astronomers regularly monitor for outbursts using either optical or radio telescopes. In August 2015, the largest recorded flares of the star occurred, with the star becoming 8.3 times brighter than normal on 13 August, in the B ;band (blue light region) . Alpha Centauri may be inside the G-cloud of the Local Bubble , and its nearest known system
2600-553: A fifth component of the Rigel system. William Herschel discovered Rigel to be a visual double star on 1 October 1781, cataloguing it as star 33 in the "second class of double stars" in his Catalogue of Double Stars, usually abbreviated to H II 33, or as H 2 33 in the Washington Double Star Catalogue. Friedrich Georg Wilhelm von Struve first measured the relative position of
2730-492: A fraction of a degree since Ptolemy 's time due to proper motion .) In Ptolemy's time, Alpha Centauri was visible from Alexandria, Egypt , at 31° N, but, due to precession , its declination is now –60° 51′ South , and it can no longer be seen at that latitude. English explorer Robert Hues brought Alpha Centauri to the attention of European observers in his 1592 work Tractatus de Globis , along with Canopus and Achernar , noting: Now, therefore, there are but three Stars of
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#17327727003922860-453: A high proper motion. In this case, the apparent stellar motion was found using Nicolas Louis de Lacaille 's astrometric observations of 1751–1752, by the observed differences between the two measured positions in different epochs. Calculated proper motion of the centre of mass for α 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
2990-787: A mass of 24 ± 8 M ☉ . Although Rigel is often considered the most luminous star within 1,000 light-years of the Sun, its energy output is poorly known. Using the Hipparcos distance of 860 light-years (264 parsecs), the estimated relative luminosity for Rigel is about 120,000 times that of the Sun ( L ☉ ), but another recently published distance of 1,170 ± 130 light-years (360 ± 40 parsecs) suggests an even higher luminosity of 219,000 L ☉ . Other calculations based on theoretical stellar evolutionary models of Rigel's atmosphere give luminosities anywhere between 83,000 L ☉ and 363,000 L ☉ , while summing
3120-466: 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. Alpha Centauri is a triple star system, with its two main stars, A and B, together comprising
3250-508: A neutron star. The earliest known recording of the name Rigel is in the Alfonsine tables of 1521. It is derived from the Arabic name Rijl Jauzah al Yusrā , "the left leg (foot) of Jauzah" (i.e. rijl meaning "leg, foot"), which can be traced to the 10th century. "Jauzah" was a proper name for Orion; an alternative Arabic name was رجل الجبار rijl al-jabbār , "the foot of
3380-922: A non-hierarchical system by this method, the same subsystem number will be used more than once; for example, a system with three visual components, A, B, and C, no two of which can be grouped into a subsystem, would have two subsystems numbered 1 denoting the two binaries AB and AC. In this case, if B and C were subsequently resolved into binaries, they would be given the subsystem numbers 12 and 13. The current nomenclature for double and multiple stars can cause confusion as binary stars discovered in different ways are given different designations (for example, discoverer designations for visual binary stars and variable star designations for eclipsing binary stars), and, worse, component letters may be assigned differently by different authors, so that, for example, one person's A can be another's C . Discussion starting in 1999 resulted in four proposed schemes to address this problem: For
3510-406: A number of more complicated arrangements. These arrangements can be organized by what Evans (1968) called mobile diagrams , which look similar to ornamental mobiles hung from the ceiling. Examples of hierarchical systems are given in the figure to the right ( Mobile diagrams ). Each level of the diagram illustrates the decomposition of the system into two or more systems with smaller size. Evans calls
3640-600: A passing comet from his station in Puducherry . Alpha Centauri was only the third binary star to be discovered, preceded by Mizar AB and Acrux . 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
3770-418: A period of 1,928 days (5.28 yr). In June 2020, a possible direct imaging detection of the planet hinted at the presence of a large ring system. However, a 2022 study disputed the existence of this planet. A 2020 paper refining Proxima b's mass excludes the presence of extra companions with masses above 0.6 M E at periods shorter than 50 days, but the authors detected a radial-velocity curve with
3900-460: A period of about 22 days. The radial velocity has since been measured to vary by about 10 km/s around a mean of 21.5 km/s . In 1933, the Hα line in Rigel's spectrum was seen to be unusually weak and shifted 0.1 nm towards shorter wavelengths, while there was a narrow emission spike about 1.5 nm to the long wavelength side of the main absorption line. This is now known as
4030-424: A periodicity of 5.15 days, suggesting the presence of a planet with a mass of about 0.29 M E . This planet, Proxima Centauri d, was confirmed in 2022. In 2021, a candidate planet named Candidate 1 (or 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
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4160-516: A possible period of 2.075 days. Rigel was observed with the Canadian MOST satellite for nearly 28 days in 2009. Milli-magnitude variations were observed, and gradual changes in flux suggest the presence of long-period pulsation modes. From observations of the variable Hα spectral line, Rigel's mass-loss rate due to stellar wind is estimated be (1.5 ± 0.4) × 10 solar masses per year ( M ☉ /yr)—about ten million times more than
4290-421: A radius of 5 R 🜨 at 1–3 AU . Multiple observations every 3–6 months could push the limit down to 3 R 🜨 . 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 0.5–2.5 AU . Candidate 1 has an estimated radius between 3.3–11 R 🜨 and orbits at 1.1 AU . It
4420-416: A single star. In these systems there is little interaction between the orbits and the stars' motion will continue to approximate stable Keplerian orbits around the system's center of mass, unlike the unstable trapezia systems or the even more complex dynamics of the large number of stars in star clusters and galaxies . In a physical triple star system, each star orbits the center of mass of
4550-552: A somewhat unreliable parallax for Rigel B, placing it at about 1,100 light-years (340 parsecs), further away than the Hipparcos distance for Rigel, but similar to the Taurus-Orion R1 association. There is no parallax for Rigel in Gaia DR2. The Gaia DR2 proper motions for Rigel B and the Hipparcos proper motions for Rigel are both small, although not quite the same. In 1871, Sherburne Wesley Burnham suspected Rigel B to be
4680-575: A speed with respect to the Sun of 32.4 km/s (20.1 mi/s), very close to the peak in the distribution of speeds of nearby stars. Since α 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, α 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
4810-406: A star of 24 ± 3 M ☉ seven to nine million years ago. Rigel's distance from the Sun is somewhat uncertain, different estimates being obtained by different methods. Old estimates placed it 166 parsecs (or 541 light years) away from the Sun. The 2007 Hipparcos new reduction of Rigel's parallax is 3.78 ± 0.34 mas , giving a distance of 863 light-years (265 parsecs) with
4940-445: A supergiant. It is expected to end its life as a type II supernova , leaving a neutron star or a black hole as a final remnant, depending on the initial mass of the star. Rigel varies slightly in brightness, its apparent magnitude ranging from 0.05 to 0.18. It is classified as an Alpha Cygni variable due to the amplitude and periodicity of its brightness variation, as well as its spectral type. Its intrinsic variability
5070-465: A system in which each subsystem in a mobile diagram is encoded by a sequence of digits. In the mobile diagram (d) above, for example, the widest system would be given the number 1, while the subsystem containing its primary component would be numbered 11 and the subsystem containing its secondary component would be numbered 12. Subsystems which would appear below this in the mobile diagram will be given numbers with three, four, or more digits. When describing
5200-659: Is circumpolar and never sets below the horizon. 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 . The star culminates each year at local midnight on 24 April and at local 9 p.m. on 8 June. As seen from Earth, Proxima Centauri
5330-416: Is 18 to 24 times as massive , depending on the method and assumptions used. Its radius is more than seventy times that of the Sun , and its surface temperature is 12,100 K . Due to its stellar wind , Rigel's mass-loss is estimated to be ten million times that of the Sun. With an estimated age of seven to nine million years, Rigel has exhausted its core hydrogen fuel, expanded, and cooled to become
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5460-637: Is 2.2° southwest from α Centauri AB ; this distance is about four times the angular diameter of the Moon . Proxima Centauri appears as a deep-red star of a typical apparent magnitude of 11.1 in a sparsely populated star field, requiring moderately sized telescopes to be seen. Listed as V645 Cen in the General Catalogue of Variable Stars , version 4.2, this UV Ceti star or "flare star" can unexpectedly brighten rapidly by as much as 0.6 magnitude at visual wavelengths, then fade after only
5590-649: Is 35.6 AU (5.33 × 10 ^ km), about the distance between the Sun and Pluto. 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
5720-602: Is 63 years. Burnham listed the Rigel multiple system as β 555 in his double star catalog or BU 555 in modern use. Component B is a double-lined spectroscopic binary system, which shows two sets of spectral lines combined within its single stellar spectrum . Periodic changes observed in relative positions of these lines indicate an orbital period of 9.86 days. The two spectroscopic components Rigel Ba and Rigel Bb cannot be resolved in optical telescopes but are known to both be hot stars of spectral type around B9. This spectroscopic binary, together with
5850-495: Is a first-magnitude star and is fainter only than Sirius and Canopus . It is the outer star of The Pointers or The Southern Pointers , so called because the line through Beta Centauri (Hadar/Agena), some 4.5° west, points to the constellation Crux —the Southern Cross. The Pointers easily distinguish the true Southern Cross from the fainter asterism known as the False Cross . South of about 29° South latitude, α Cen
5980-426: Is a runaway star with a complex history and might have originally formed in the main body of the association. Hierarchical scheme for Rigel's components The star system of which Rigel is a part has at least four components. Rigel (sometimes called Rigel A to distinguish from the other components) has a visual companion , which is likely a close triple-star system. A fainter star at a wider separation might be
6110-417: Is a defining point of the classification sequence for supergiants. The overall spectrum is typical for a late B class star, with strong absorption lines of the hydrogen Balmer series as well as neutral helium lines and some of heavier elements such as oxygen, calcium, and magnesium. The luminosity class for B8 stars is estimated from the strength and narrowness of the hydrogen spectral lines, and Rigel
6240-643: Is almost always brighter than α Orionis ( Betelgeuse ). Astronomer J.B. Kaler speculated that Bayer assigned letters during a rare period when variable star Betelgeuse temporarily outshone Rigel, resulting in Betelgeuse being designated "alpha" and Rigel designated "beta". However, closer examination of Bayer's method shows that he did not strictly order the stars by brightness, but instead grouped them first by magnitude, then by declination . Rigel and Betelgeuse were both classed as first magnitude , and in Orion
6370-488: Is also the first star of Orion to set in most of the Northern Hemisphere. The star is a vertex of the " Winter Hexagon ", an asterism that includes Aldebaran , Capella , Pollux , Procyon , and Sirius . Rigel is a prominent equatorial navigation star , being easily located and readily visible in all the world's oceans (the exception is the area north of the 82nd parallel north ). Rigel's spectral type
6500-446: Is an example of a physical hierarchical triple system, which has an outer star orbiting an inner physical binary composed of two more red dwarf stars. Triple stars that are not all gravitationally bound might comprise a physical binary and an optical companion (such as Beta Cephei ) or, in rare cases, a purely optical triple star (such as Gamma Serpentis ). Hierarchical multiple star systems with more than three stars can produce
6630-560: Is an outlying member of the Orion OB1 association , which is located at a distance of up to 1,600 light-years (500 parsecs) from Earth. It is a member of the loosely defined Taurus-Orion R1 Association , somewhat closer at 1,200 light-years (360 parsecs). Rigel is thought to be considerably closer than most of the members of Orion OB1 and the Orion Nebula . Betelgeuse and Saiph lie at a similar distance to Rigel, although Betelgeuse
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#17327727003926760-523: Is approximately 511 000 +41 000 −30 000 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 12 300 +200 −100 AU . Asteroseismic studies, chromospheric activity , and stellar rotation ( gyrochronology ) are all consistent with the Alpha Centauri system being similar in age to, or slightly older than,
6890-469: Is assigned to the bright supergiant class Ia. Variations in the spectrum have resulted in the assignment of different classes to Rigel, such as B8 Ia, B8 Iab, and B8 Iae. As early as 1888, the heliocentric radial velocity of Rigel, as estimated from the Doppler shifts of its spectral lines, was seen to vary. This was confirmed and interpreted at the time as being due to a spectroscopic companion with
7020-446: Is believed to be in a region of nebulosity , its radiation illuminating several nearby clouds. Most notable of these is the 5°-long IC 2118 (Witch Head Nebula), located at an angular separation of 2.5° from the star, or a projected distance of 39 light-years (12 parsecs) away. From measures of other nebula-embedded stars, IC 2118's distance is estimated to be 949 ± 7 light-years (291 ± 2 parsecs). Rigel
7150-451: Is called a hierarchical system : the stars in the system can be divided into two smaller groups, each of which traverses a larger orbit around the system's center of mass . Each of these smaller groups must also be hierarchical, which means that they must be divided into smaller subgroups which themselves are hierarchical, and so on. Each level of the hierarchy can be treated as a two-body problem by considering close pairs as if they were
7280-405: Is caused by stellar pulsations similar to those of Deneb . Further observations of radial velocity variations indicate that it simultaneously oscillates in at least 19 non-radial modes with periods ranging from about 1.2 to 74 days. Estimation of many physical characteristics of blue supergiant stars, including Rigel, is challenging due to their rarity and uncertainty about how far they are from
7410-413: Is caused by pulsations in its unstable atmosphere. Rigel is generally the seventh-brightest star in the night sky and the brightest star in Orion, though it is occasionally outshone by Betelgeuse , which varies over a larger range. A triple-star system is separated from Rigel by an angle of 9.5 arc seconds . It has an apparent magnitude of 6.7, making it 1/400th as bright as Rigel. Two stars in
7540-413: Is comparable to that of the Sun, showing coronal variability due to star spots , as modulated by the rotation of the star. However, since 2005 the activity level has fallen into a deep minimum that might be similar to the Sun's historical Maunder Minimum . Alternatively, it may have a very long stellar activity cycle and is slowly recovering from a minimum phase. Alpha Centauri B, also known as Toliman,
7670-414: Is controversial. α 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. α Centauri B has no known planets: Planet α Cen Bb , purportedly discovered in 2012, was later disproven, and no other planet has yet been confirmed. α Centauri ( Latinised to Alpha Centauri )
7800-453: Is generally called a star cluster or galaxy , although, broadly speaking, they are also star systems. Star systems are not to be confused with planetary systems , which include planets and similar bodies (such as comets ). A star system of two stars is known as a binary star , binary star system or physical double star . If there are no tidal effects, no perturbation from other forces, and no transfer of mass from one star to
7930-522: Is likely to be fusing helium in its core. Due to strong convection of helium produced in the core while Rigel was on the main sequence and in the hydrogen-burning shell since it became a supergiant, the fraction of helium at the surface has increased from 26.6% when the star formed to 32% now. The surface abundances of carbon, nitrogen, and oxygen seen in the spectrum are compatible with a post-red supergiant star only if its internal convection zones are modeled using non-homogeneous chemical conditions known as
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#17327727003928060-510: Is listed in the General Catalogue of Variable Stars , but since its familiar Bayer designation is used instead of creating a separate variable star designation . Rigel is an intrinsic variable star with an apparent magnitude ranging from 0.05 to 0.18. It is typically the seventh-brightest star in the celestial sphere , excluding the Sun, although occasionally fainter than Betelgeuse. Rigel appears slightly blue-white and has
8190-479: 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. Alpha Centauri B has an apparent magnitude of +1.35, slightly dimmer than Mimosa . 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
8320-414: Is part of the α Centauri system and slightly closer to Earth than α Centauri AB . As such, Innes concluded that Proxima Centauri was the closest star to Earth yet discovered. All components of α Centauri display significant proper motion against the background sky. Over centuries, this causes their apparent positions to slowly change. Proper motion was unknown to ancient astronomers. Most assumed that
8450-480: Is similar, the AB binary system is sometimes treated as a single gravitational object. The A and B components of Alpha Centauri have an orbital period of 79.762 years. Their orbit is moderately eccentric , as it has an eccentricity of almost 0.52; their closest approach or periastron is 11.2 AU (1.68 × 10 ^ km), or about the distance between the Sun and Saturn; and their furthest separation or apastron
8580-406: Is smaller and cooler, at 0.9 solar mass and less than 0.5 solar luminosity. The pair orbit around a common centre with an orbital period of 79 years. Their elliptical orbit is eccentric , so that the distance between A and B varies from 35.6 astronomical units ( AU ), or about the distance between Pluto and the Sun, to 11.2 AU , or about the distance between Saturn and
8710-417: Is the binary brown dwarf system Luhman 16 , at 3.6 light-years (1.1 parsecs ) from Alpha Centauri. Alpha Centauri is listed in the 2nd century the star catalog appended to Ptolemy 's Almagest . He gave its ecliptic coordinates , but texts differ as to whether the ecliptic latitude reads 44° 10′ South or 41° 10′ South . (Presently the ecliptic latitude is 43.5° South , but it has decreased by
8840-399: Is the brightest and most massive component – and the eponym – of a star system of at least four stars that appear as a single blue-white point of light to the naked eye . This system is located at a distance of approximately 860 light-years (260 pc ) from the Sun. A star of spectral type B8Ia, Rigel is 120,000 times as luminous as the Sun, and
8970-527: Is the principal member, or primary, of the binary system. It is a solar-like main-sequence star with a similar yellowish colour, whose stellar classification is spectral type G2-V; it is about 10% more massive than the Sun, with a radius about 22% larger. When considered among the individual brightest stars in the night sky, it is the fourth-brightest at an apparent magnitude of +0.01, being slightly fainter than Arcturus at an apparent magnitude of −0.05. The type of magnetic activity on Alpha Centauri A
9100-468: 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; 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. Its light curve varies on a short time scale, and there has been at least one observed flare . It
9230-608: Is the system's designation given by J. 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 . The common name Rigil Kentaurus is a Latinisation of the Arabic translation رجل القنطورس Rijl al-Qinṭūrus, meaning "the Foot of
9360-408: Is therefore likely within the reach of JWST observations. The first claim of a planet around Alpha Centauri B was that of Alpha Centauri Bb in 2012, which was proposed to be an Earth-mass planet in a 3.2-day orbit. This was refuted in 2015 when the apparent planet was shown to be an artifact of the way the radial velocity data was processed. A search for transits of planet Bb was conducted with
9490-577: The Centaur ". Qinṭūrus is the Arabic transliteration of the Greek Κένταυρος (Kentaurus). The name is frequently abbreviated to Rigil Kent ( / ˈ r aɪ dʒ əl ˈ k ɛ n t / ) or even Rigil , though the latter name is better known for Rigel ( β Orionis). 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
9620-783: The Chinese name for Alpha Centauri itself is 南門二 Nán Mén Èr , the Second Star of the Southern Gate. To the Indigenous Boorong people of northwestern Victoria in Australia, Alpha Centauri and Beta Centauri are Bermbermgle , two brothers noted for their courage and destructiveness, who speared and killed Tchingal "The Emu" (the Coalsack Nebula ). The form in Wotjobaluk is Bram-bram-bult . To
9750-512: The European Southern Observatory (ESO). It has an estimated minimum mass of 1.17 M E ( Earth masses ) and orbits approximately 0.049 AU from Proxima Centauri, placing it in the star's habitable zone . The discovery of Proxima Centauri c was formally published in 2020 and could be a super-Earth or mini-Neptune . It has a mass of roughly 7 M E and orbits about 1.49 AU from Proxima Centauri with
9880-711: The Hubble Space Telescope from 2013 to 2014. This search detected one potential transit-like event, which could be associated with a different planet 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. It could have lakes of molten lava and would be far too close to Alpha Centauri B to harbour life . If confirmed, this planet might be called Alpha Centauri Bc . However,
10010-628: The IAU approved the name Toliman ( / ˈ t ɒ l ɪ m æ n / ) for α Centauri B . During the 19th century, the northern amateur popularist E.H. Burritt used the now-obscure name Bungula ( / ˈ b ʌ ŋ ɡ juː l ə / ). 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). In Chinese astronomy , 南門 Nán Mén , meaning Southern Gate , refers to an asterism consisting of Alpha Centauri and Epsilon Centauri . Consequently,
10140-474: The Ledoux Criteria . Rigel is expected to eventually end its stellar life as a type II supernova . It is one of the closest known potential supernova progenitors to Earth, and would be expected to have a maximum apparent magnitude of around −11 (about the same brightness as a quarter Moon or around 300 times brighter than Venus ever gets). The supernova would leave behind either a black hole or
10270-610: The Trapezium cluster in the Orion Nebula some two million years ago. The components of multiple stars can be specified by appending the suffixes A , B , C , etc., to the system's designation. Suffixes such as AB may be used to denote the pair consisting of A and B . The sequence of letters B , C , etc. may be assigned in order of separation from the component A . Components discovered close to an already known component may be assigned suffixes such as Aa , Ba , and so forth. A. A. Tokovinin's Multiple Star Catalogue uses
10400-532: The Working Group on Star Names of the IAU, having decided to attribute proper names to individual component stars rather than to multiple systems , approved the name Rigil Kentaurus ( / ˈ r aɪ dʒ əl k ɛ n ˈ t ɔːr ə s / ) as being restricted to α Centauri A and the name Proxima Centauri ( / ˈ p r ɒ k s ɪ m ə s ɛ n ˈ t ɔːr aɪ / ) for α Centauri C . On 10 August 2018,
10530-439: The binary star system α Centauri AB . To the naked eye , these two main components appear to be a single star with an apparent magnitude of −0.27 . It is the brightest star in the constellation and the third-brightest in the night sky , outshone by only Sirius and Canopus . α Centauri A (Rigil Kentaurus) has 1.1 times the mass and 1.5 times the luminosity of the Sun , while α Centauri B (Toliman)
10660-568: The spectral energy distribution from historical photometry with the Hipparcos distance suggests a luminosity as low as 61,515 ± 11,486 L ☉ . A 2018 study using the Navy Precision Optical Interferometer measured the angular diameter as 2.526 mas . After correcting for limb darkening , the angular diameter is found to be 2.606 ± 0.009 mas , yielding a radius of 74.1 +6.1 −7.3 R ☉ . An older measurement of
10790-513: The 'e' indicates that it displays emission lines in its spectrum, while the 'p' means it has an unspecified spectral peculiarity. Alpha Cygni type variables are generally considered to be irregular or have quasi-periods . Rigel was added to the General Catalogue of Variable Stars in the 74th name-list of variable stars on the basis of the Hipparcos photometry, which showed variations with a photographic amplitude of 0.039 magnitudes and
10920-400: The AB system between April 1832 and May 1833. He withheld his results, however, because he suspected they were too large to be true, but eventually published them in 1839 after Bessel released his own accurately determined parallax for 61 Cygni in 1838. For this reason, Alpha Centauri is sometimes considered as the second star to have its distance measured because Henderson's work
11050-460: 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. All the observational studies have so far failed to find evidence for brown dwarfs or gas giants . 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 0.5–0.9 AU from
11180-415: The IAU describes such names as "useful nicknames" that are "unofficial". In modern comprehensive catalogs, the whole multiple star system is known as WDS 05145-0812 or CCDM 05145–0812. The designation of Rigel as β Orionis ( Latinized to beta Orionis ) was made by Johann Bayer in 1603. The "beta" designation is usually given to the second-brightest star in each constellation, but Rigel
11310-652: The PA of 337.1°, increasing to 5.49 arcsec through 345.3° in 2020. The closest recent approach was in February 2016, at 4.0 arcsec through the PA of 300°. The observed maximum separation of these stars is about 22 arcsec, while the minimum distance is 1.7 arcsec. The widest separation occurred during February 1976, and the next will be in January 2056. Alpha Centauri C is about 13,000 AU (0.21 ly; 1.9 × 10 ^ km) from Alpha Centauri AB, equivalent to about 5% of
11440-489: The Red Kangaroo Leader Unumburrgu and chief conductor of ceremonies in a songline when Orion is high in the sky. Eridanus , the river, marks a line of stars in the sky leading to it, and the other stars of Orion are his ceremonial tools and entourage. Betelgeuse is Ya-jungin "Owl Eyes Flicking", watching the ceremonies. The Māori people of New Zealand named Rigel as Puanga , said to be
11570-626: The South Island. In Japan, the Minamoto or Genji clan chose Rigel and its white color as its symbol, calling the star Genji-boshi ( 源氏星 ), while the Taira or Heike clan adopted Betelgeuse and its red color. The two powerful families fought the Genpei War ; the stars were seen as facing off against each other and kept apart only by the three stars of Orion's Belt . The MS Rigel
11700-657: The Sun at 5 to 6 billion years, as derived by their mass and spectral characteristics. From the orbital elements , the total mass of Alpha Centauri AB is about 2.0 M ☉ – or twice that of the Sun. The average individual stellar masses are about 1.08 M ☉ and 0.91 M ☉ , respectively, though slightly different masses have also been quoted in recent years, such as 1.14 M ☉ and 0.92 M ☉ , totaling 2.06 M ☉ . Alpha Centauri A and B have absolute magnitudes of +4.38 and +5.71, respectively. Alpha Centauri A, also known as Rigil Kentaurus,
11830-426: The Sun. α Centauri C , or more commonly, 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 α Centauri AB . Currently, the distance between Proxima Centauri and α Centauri AB is about 13,000 AU (0.21 ly), equivalent to about 430 times
11960-401: The Sun. As such, their characteristics are mainly estimated from theoretical stellar evolution models . Its effective temperature can be estimated from the spectral type and color to be around 12,100 K . A mass of 21 ± 3 M ☉ at an age of 8 ± 1 million years has been estimated by comparing evolutionary tracks, while atmospheric modeling from the spectrum gives
12090-477: The Sun. Asteroseismic analyses that incorporate tight observational constraints on the stellar parameters for the Alpha Centauri stars have yielded age estimates of 4.85 ± 0.5 Gyr, 5.0 ± 0.5 Gyr, 5.2 ± 1.9 Gyr, 6.4 Gyr, and 6.52 ± 0.3 Gyr. Age estimates for the stars based on chromospheric activity (Calcium H & K emission) yield 4.4 ± 2.1 Gyr, whereas gyrochronology yields 5.0 ± 0.3 Gyr. Stellar evolution theory implies both stars are slightly older than
12220-456: The Sun. Its mass is calculated to be 0.1221 M ☉ . It is the closest star to the Sun but is too faint to be visible to the naked eye. 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. Proxima Centauri b is a terrestrial planet discovered in 2016 by astronomers at
12350-436: The angular diameter gives 2.75 ± 0.01 mas , equivalent to a radius of 78.9 R ☉ at 264 pc . These radii are calculated assuming the Hipparcos distance of 264 pc ; adopting a distance of 360 pc leads to a significantly larger size. Older distance estimates were mostly far lower than modern estimates, leading to lower radius estimates; a 1922 estimate by John Stanley Plaskett gave Rigel
12480-436: The close visual component Rigel C, is likely a physical triple-star system, although Rigel C cannot be detected in the spectrum, which is inconsistent with its observed brightness. In 1878, Burnham found another possibly associated star of approximately 13th magnitude. He listed it as component D of β 555, although it is unclear whether it is physically related or a coincidental alignment. Its 2017 separation from Rigel
12610-444: The coming decades, allowing accurate measurement of proper motions and possibly giving information on planets. Based on the system's common proper motion and radial velocities, α Centauri will continue to change its position in the sky significantly and will gradually brighten. For example, in about 6,200 CE , α Centauri's true motion will cause an extremely rare first-magnitude stellar conjunction with Beta Centauri , forming
12740-401: The companion in 1822, cataloguing the visual pair as Σ 668. The secondary star is often referred to as Rigel B or β Orionis B. The angular separation of Rigel B from Rigel A is 9.5 arc seconds to its south along position angle 204°. Although not particularly faint at visual magnitude 6.7, the overall difference in brightness from Rigel A (about 6.6 magnitudes or 440 times fainter) makes it
12870-550: The constellation representing the mythological Greek huntsman Orion , Rigel is his knee or (as its name suggests) foot; with the nearby star Beta Eridani marking Orion's footstool. Rigel is presumably the star known as " Aurvandil 's toe" in Norse mythology . In the Caribbean, Rigel represented the severed leg of the folkloric figure Trois Rois , himself represented by the three stars of Orion's Belt. The leg had been severed with
13000-414: The distance between Alpha Centauri AB and the Sun. 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. The orbital period of Proxima Centauri
13130-515: The first level of the hierarchy, lower-case letters (a, b, ...) for the second level, and numbers (1, 2, ...) for the third. Subsequent levels would use alternating lower-case letters and numbers, but no examples of this were found in the sample. Rigel Rigel is a blue supergiant star in the constellation of Orion . It has the Bayer designation β Orionis , which is Latinized to Beta Orionis and abbreviated Beta Ori or β Ori . Rigel
13260-591: 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 . The binary nature of Alpha Centauri AB was recognized in December 1689 by Jean Richaud, while observing
13390-460: The great one", from which stems the rarely used variant names Algebar or Elgebar . The Alphonsine tables saw its name split into "Rigel" and "Algebar", with the note, et dicitur Algebar. Nominatur etiam Rigel. Alternate spellings from the 17th century include Regel by Italian astronomer Giovanni Battista Riccioli , Riglon by German astronomer Wilhelm Schickard , and Rigel Algeuze or Algibbar by English scholar Edmund Chilmead . With
13520-639: The inner pair every 63 years. A much fainter star, separated from Rigel and the others by nearly an arc minute , may be part of the same star system. In 2016, the International Astronomical Union (IAU) included the name "Rigel" in the IAU Catalog of Star Names. According to the IAU, this proper name applies only to the primary component A of the Rigel system. The system is listed variously in historical astronomical catalogs as H II 33, Σ 668, β 555, or ADS 3823. For simplicity, Rigel's companions are referred to as Rigel B, C, and D;
13650-503: The lack of any brown dwarfs or gas giants in close orbits around Alpha Centauri make the likelihood of terrestrial planets greater than otherwise. A theoretical study indicates that a radial velocity analysis might detect a hypothetical planet of 1.8 M E in Alpha Centauri B's habitable zone . Star system A star system or stellar system is a small number of stars that orbit each other, bound by gravitational attraction . A large group of stars bound by gravitation
13780-407: The main star. α Centauri C was discovered in 1915 by Robert T. A. Innes , who suggested that it be named Proxima Centaurus , from Latin 'the nearest [star] of Centaurus '. The name Proxima Centauri later became more widely used and is now listed by the International Astronomical Union (IAU) as the approved proper name; commonly, it is frequently abbreviated to Proxima . In 2016,
13910-446: The mass-loss rate from the Sun . More detailed optical and K band infrared spectroscopic observations, together with VLTI interferometry, were taken from 2006 to 2010. Analysis of the Hα and Hγ line profiles, and measurement of the regions producing the lines, show that Rigel's stellar wind varies greatly in structure and strength. Loop and arm structures were also detected within
14040-488: The naked eye, α Centauri AB appears to be a single star, the brightest in the southern constellation of Centaurus . Their apparent angular separation varies over about 80 years between 2 and 22 arcseconds (the naked eye has a resolution of 60 arcsec), but through much of the orbit, both are easily resolved in binoculars or small telescopes. At −0.27 apparent magnitude (combined for A and B magnitudes (see Apparent magnitude § Magnitude addition ) ), Alpha Centauri
14170-429: The name has not been used in the literature, as it is not a claimed discovery. 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
14300-481: The number of known systems with a given multiplicity decreases exponentially with multiplicity. For example, in the 1999 revision of Tokovinin's catalog of physical multiple stars, 551 out of the 728 systems described are triple. However, because of suspected selection effects , the ability to interpret these statistics is very limited. Multiple-star systems can be divided into two main dynamical classes: or Most multiple-star systems are organized in what
14430-417: The other, such a system is stable, and both stars will trace out an elliptical orbit around the barycenter of the system indefinitely. (See Two-body problem ) . Examples of binary systems are Sirius , Procyon and Cygnus X-1 , the last of which probably consists of a star and a black hole . A multiple star system consists of two or more stars that appear from Earth to be close to one another in
14560-432: 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. 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
14690-502: The process may eject components as galactic high-velocity stars . They are named after the multiple star system known as the Trapezium Cluster in the heart of the Orion Nebula . Such systems are not rare, and commonly appear close to or within bright nebulae . These stars have no standard hierarchical arrangements, but compete for stable orbits. This relationship is called interplay . Such stars eventually settle down to
14820-415: The pulsations of Rigel are powered by nuclear reactions in a hydrogen-burning shell that is at least partially non-convective. These pulsations are stronger and more numerous in stars that have evolved through a red supergiant phase and then increased in temperature to again become a blue supergiant. This is due to the decreased mass and increased levels of fusion products at the surface of the star. Rigel
14950-654: The quantity and velocity of material being expelled from the star. Occasional very high-velocity outflows have been inferred, and, more rarely, infalling material. The overall picture is one of large looping structures arising from the photosphere and driven by magnetic fields. Rigel has been known to vary in brightness since at least 1930. The small amplitude of Rigel's brightness variation requires photoelectric or CCD photometry to be reliably detected. This brightness variation has no obvious period. Observations over 18 nights in 1984 showed variations at red, blue, and yellow wavelengths of up to 0.13 magnitudes on timescales of
15080-423: The radius of Neptune's orbit. Proxima Centauri has two confirmed planets: Proxima b or α Centauri Cb , an Earth-sized planet in the habitable zone discovered in 2016, and Proxima d ( α Centauri Cd ) , a candidate sub-Earth which orbits very closely to the star, announced in 2022. The existence of Proxima c ( α Centauri Cc ) , a mini-Neptune 1.5 AU away discovered in 2019,
15210-468: The relative places of the stars from a binary star ephemeris . Others, like D. Pourbaix (2002), have regularly refined the precision of new published orbital elements. 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 α Centauri AB, which suggested that Proxima Centauri
15340-1002: The sky. This may result from the stars actually being physically close and gravitationally bound to each other, in which case it is a physical multiple star, or this closeness may be merely apparent, in which case it is an optical multiple star Physical multiple stars are also commonly called multiple stars or multiple star systems . Most multiple star systems are triple stars . Systems with four or more components are less likely to occur. Multiple-star systems are called triple , ternary , or trinary if they contain 3 stars; quadruple or quaternary if they contain 4 stars; quintuple or quintenary with 5 stars; sextuple or sextenary with 6 stars; septuple or septenary with 7 stars; octuple or octenary with 8 stars. These systems are smaller than open star clusters , which have more complex dynamics and typically have from 100 to 1,000 stars. Most multiple star systems known are triple; for higher multiplicities,
15470-435: 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 star cluster ), would permit an accretion-friendly environment farther from the star. Bodies around Alpha Centauri A would be able to orbit at slightly farther distances due to its stronger gravity. In addition,
15600-610: The stars of each class appear to have been ordered north to south. Rigel has many other stellar designations taken from various catalogs, including the Flamsteed 19 Orionis (19 Ori), the Bright Star Catalogue entry HR 1713, and the Henry Draper Catalogue number HD 34085. These designations frequently appear in the scientific literature, but rarely in popular writing. Rigel
15730-413: The stars were permanently fixed on the celestial sphere , as stated in the works of the philosopher Aristotle. In 1718, Edmond Halley found that some stars had significantly moved from their ancient astrometric positions. In the 1830s, Thomas Henderson discovered the true distance to α Centauri by analysing his many astrometric mural circle observations. He then realised this system also likely had
15860-408: The system can be seen by large telescopes, and the brighter of the two is a spectroscopic binary . These three stars are all blue-white main-sequence stars , each three to four times as massive as the Sun. Rigel and the triple system orbit a common center of gravity with a period estimated to be 24,000 years. The inner stars of the triple system orbit each other every 10 days, and the outer star orbits
15990-400: The system. Usually, two of the stars form a close binary system , and the third orbits this pair at a distance much larger than that of the binary orbit. This arrangement is called hierarchical . The reason for this arrangement is that if the inner and outer orbits are comparable in size, the system may become dynamically unstable, leading to a star being ejected from the system. EZ Aquarii
16120-432: The time, it is a double-peaked line, that is, an absorption line with an emission core or an emission line with an absorption core. About a quarter of the time it has a P Cygni profile; most of the rest of the time, the line has an inverse P Cygni profile, where the emission component is on the short wavelength side of the line. Rarely, there is a pure emission Hα line. The line profile changes are interpreted as variations in
16250-472: The wind. Calculations of mass loss from the Hγ line give (9.4 ± 0.9) × 10 M ☉ /yr in 2006-7 and (7.6 ± 1.1) × 10 M ☉ /yr in 2009–10. Calculations using the Hα line give lower results, around 1.5 × 10 M ☉ /yr . The terminal wind velocity is 300 km/s . It is estimated that Rigel has lost about three solar masses ( M ☉ ) since beginning life as
16380-405: Was 44.5 ″ , almost due north at a position angle of 1°. Gaia DR2 finds it to be a 12th magnitude sunlike star at approximately the same distance as Rigel. Likely a K-type main-sequence star , this star would have an orbital period of around 250,000 years, if it is part of the Rigel system. A spectroscopic companion to Rigel was reported on the basis of radial velocity variations, and its orbit
16510-581: Was discussed again at the 25th General Assembly in 2003, and it was again resolved by commissions 5, 8, 26, 42, and 45, as well as the Working Group on Interferometry, that the WMC scheme should be expanded and further developed. The sample WMC is hierarchically organized; the hierarchy used is based on observed orbital periods or separations. Since it contains many visual double stars , which may be optical rather than physical, this hierarchy may be only apparent. It uses upper-case letters (A, B, ...) for
16640-556: Was even calculated, but subsequent work suggests the star does not exist and that observed pulsations are intrinsic to Rigel itself. Rigel is a blue supergiant that has exhausted the hydrogen fuel in its core, expanded and cooled as it moved away from the main sequence across the upper part of the Hertzsprung–Russell diagram . When it was on the main sequence, its effective temperature would have been around 30,000 K . Rigel's complex variability at visual wavelengths
16770-521: Was not fully acknowledged at first. (The distance of Alpha Centauri from the Earth is now reckoned at 4.396 light-years or 4.159 × 10 km.) Later, John Herschel made the first micrometrical observations in 1834. Since the early 20th century, measures have been made with photographic plates . By 1926, William Stephen Finsen calculated the approximate orbit elements close to those now accepted for this system. All future positions are now sufficiently accurate for visual observers to determine
16900-754: Was originally a Norwegian ship, built in Copenhagen in 1924. It was requisitioned by the Germans during World War II and sunk in 1944 while being used to transport prisoners of war. Two US Navy ships have borne the name USS Rigel . The SSM-N-6 Rigel was a cruise missile program for the US Navy that was cancelled in 1953 before reaching deployment. The Rigel Skerries are a chain of small islands in Antarctica , renamed after originally being called Utskjera. They were given their current name as Rigel
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