View source for Rigel

{{short description|Brightest star in the constellation Orion}}
{{other uses}}
{{Use dmy dates|date=August 2020}}
{{Starbox begin
| name = Rigel
}}
{{Starbox image
 | image =
  {{Location mark
  | image = Orion constellation map.svg | width = 280
  | float = center
  | mark = Red circle.svg | mark_width = 15 | mark_link = β Ori
  | x = 730 | y = 742
  }}
 | caption = Location of Rigel (circled)
}}
{{Starbox observe 2s
| epoch = J2000
| constell = [[Orion (constellation)|Orion]]
| pronounce = {{IPAc-en|ˈ|r|aɪ|dʒ|əl}}<ref name=Kunitzsch/> or {{IPAc-en|-|g|əl}}<ref name=ddc/>
| component1 = A
| ra1 = {{RA|05|14|32.27210}}<ref name=aaa474_2_653/>
| dec1 = {{DEC|−08|12|05.8981}}<ref name=aaa474_2_653/>
| appmag_v1 = 0.13 to 0.12<ref name=ducati/> {{nowrap|(0.05–0.18)<ref name=guinan/>}}
| component2 = BC
| ra2 = {{RA|05|14|32.049}}<ref name=DENIS/>
| dec2 = {{DEC|−08|12|14.78}}<ref name=DENIS/>
| appmag_v2 = 6.67<ref name=sanford/> {{nowrap|(7.5/7.6)<ref name=WDS/>}}
}}
{{Starbox character
| component1 = A
| type=[[Blue supergiant star|Blue supergiant]]
| class = B8 Ia<ref name=aaa445_3_1099/>
| b-v = −0.03<ref name=aass34_1/>
| u-b = −0.66<ref name=aass34_1/>
| variable = [[Alpha Cygni variable|Alpha Cygni]]<ref name=apj2012_749_74/>
| component2 = BC
| type2=[[Main sequence]]
| class2 = B9V + B9V<ref name=msc/>
}}
{{Starbox astrometry
| component1        = A
| radial_v          = {{val|17.8|0.4}}<ref name=Gontcharov/>
| prop_mo_ra        = +1.31<ref name=aaa474_2_653/>
| prop_mo_dec       = +0.50<ref name=aaa474_2_653/>
| parallax          = 3.78
| p_error           = 0.34
| parallax_footnote = <ref name=aaa474_2_653/>
| dist_pc = {{Val|260|20}}
| dist_ly = {{val|848|65}}
| dist_footnote = <ref name=deAlmeida/>
| absmag_v          = −7.84<ref name=aaa445_3_1099/>
}}
{{Starbox astrometry|no_heading=y
| component1         = BC
| radial_v           = {{val|17.8|0.4}}<ref name=Gontcharov/>
| prop_mo_ra         = −0.034<ref name="Gaia3"/>
| prop_mo_dec        = −0.017<ref name="Gaia3"/>
| parallax           = 3.2352
| p_error            = 0.0553
| parallax_footnote  = <ref name="Gaia3"/>
| absmag_v2          =
}}
{{Starbox orbit
| reference =<ref name=msc/>
| name=BC
| primary=A
| period=24,000
}}
{{Starbox orbit
| reference =<ref name=sanford/>
| primary = Ba
| name = Bb
| period_unitless = 9.860 days
| eccentricity = 0.1
| k1 = 25.0
| k2 = 32.6
}}
{{Starbox orbit
|reference =<ref name=msc/>
|primary=B
|name=C
|period=63
}}
{{Starbox detail
| component1 = A
| age_myr               = {{val|8|1}}<ref name=aaa445_3_1099/>
| metal_fe              = {{val|-0.06|0.10}}<ref name=aaa445_3_1099/>
| mass                  = {{val|21|3}}<ref name=schultz/>
| radius                = {{val|74.1|6.1|7.3}}<ref name=baines/>
| rotational_velocity   = {{val|25|3}}<ref name=przybilla/>
| luminosity_bolometric = {{val|120000|25000|21000|fmt=commas}}<ref name=apj2012_747_108/>
| temperature           = {{val|12100|150|fmt=commas}}<ref name=przybilla/>
| gravity               = {{val|1.75|0.10}}<ref name=przybilla/>
}}
{{Starbox detail
|no_heading=y
| component1 = Ba
| mass                  = 3.84<ref name=msc/>
| component2 = Bb
| mass2                 = 2.94<ref name=msc/>
}}
{{Starbox detail
|no_heading=y
| component1 = C
| mass                  = 3.84<ref name=msc/>
}}
{{Starbox catalog
| names = [[Bayer designation|β Orionis]], [[Aitken Double Star Catalogue|ADS]]{{spaces}}3823, [[Struve Double Star Catalog|STF]]{{spaces}}668, [[Burnham Double Star Catalogue|BU]]{{spaces}}555,<ref name=WDS/> [[Herschel Catalogue of Double Stars|H{{spaces}}II]]{{spaces}}33,<ref name="Herschel1782"/> [[Catalog of Components of Double and Multiple Stars|CCDM]]{{spaces}}J05145-0812, [[Washington Double Star Catalog|WDS]]{{spaces}}J05145-0812<ref name="simbad"/>
| component1 = A
| names1 = Rigel, Algebar, Elgebar, [[Flamsteed designation|19 Orionis]], [[Henry Draper catalogue|HD]]{{spaces}}34085, [[Harvard Revised catalogue|HR]]{{spaces}}1713, [[Hipparcos Catalogue|HIP]]{{spaces}}24436, [[Smithsonian Astrophysical Observatory Star Catalog|SAO]]{{spaces}}131907, [[Bonner Durchmusterung|BD]]−08°1063, [[Catalogues of Fundamental Stars|FK5]]{{spaces}}194
| component2 = B
| names2 = Rigel B, [[General Catalogue of Stellar Radial Velocities|GCRV]]{{spaces}}3111
}}
{{Starbox reference
| Simbad = RIGEL|sn=Rigel
| Simbad2 = bet+Ori+B|sn2=Rigel B
}}
{{Starbox end}}

'''Rigel''' is a blue [[supergiant]] star in the equatorial [[constellation]] of [[Orion (constellation)|Orion]]. It has the [[Bayer designation]] '''β Orionis''', which is [[Latinisation of names|Latinized]] to '''Beta Orionis''' and abbreviated '''Beta Ori''' or '''β Ori'''. Rigel is the brightest and most [[Massive star|massive]] component{{snd}}and the [[:wikt:eponym|eponym]]{{snd}}of a [[star system]] of at least four [[star]]s that appear as a single blue-white point of light to the [[naked eye]]. This system is located at a distance of approximately {{convert|850|ly|pc|sigfig=2|lk=on}}.

A star of [[Stellar classification#Modern classification|spectral type]] B8Ia, Rigel is calculated to be anywhere from 61,500 to 363,000 times [[Solar luminosity|as luminous]] as the Sun, and 18 to 24 times [[solar mass|as massive]], depending on the method and assumptions used. Its radius is more than seventy times [[Solar radius|that of the Sun]], and its [[Surface temperature (star)|surface temperature]] is {{val|12,100|ul=K|fmt=commas}}. Due to its [[stellar wind]], Rigel's [[Stellar mass loss|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 a [[Supergiant star|supergiant]]. It is expected to end its life as a [[type II supernova|Type{{spaces}}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 [[Variable star#Intrinsic variable stars|intrinsic variability]] is caused by pulsations in its unstable atmosphere. Rigel is generally the [[list of brightest stars|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 {{val|9.5|ul=arc seconds}}. It has an apparent magnitude of 6.7, making it 1/400th as bright as Rigel. Two stars in the system can be seen by large telescopes, and the brighter of the two is a [[spectroscopic binary]]. These three stars are all [[B-type main-sequence star|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 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.

== Nomenclature ==
[[File:Orion Head to Toe.jpg|thumb|left|alt=Bright points of light against a dark background with wisps of colored nebulosity|[[Orion (constellation)|Orion]], with Rigel at bottom right, at optical wavelengths plus the Hα ([[hydrogen-alpha]]) spectral line to emphasize gas clouds]]

In 2016, the [[International Astronomical Union]] (IAU) included the name "Rigel" in the IAU Catalog of Star Names.<ref name="IAU-CSN"/><ref name="WGSN2018"/> 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 [[Herschel Catalogue of Double Stars|H{{spaces}}II]]{{spaces}}33, [[Struve Double Star Catalog|Σ]]{{spaces}}668, [[Burnham Double Star Catalogue|β]]{{spaces}}555, or [[Aitken Double Star Catalogue|ADS]]{{spaces}}3823. For simplicity, Rigel's companions are referred to as Rigel B,<ref name="WGSN2018"/> C, and D;<ref name="kalerrigel" /><ref name="garfinkle1997"/> the IAU describes such names as "useful nicknames" that are "unofficial".<ref name="WGSN2018"/> In modern comprehensive catalogs, the whole multiple star system is known as [[Washington Double Star Catalog|WDS]] 05145-0812 or [[Catalog of Components of Double and Multiple Stars|CCDM]] 05145–0812.<ref name=WDS/><ref name=CCDM/><!--SIMBAD adds J; i.e. WDS J05145-0812 or CCDM J05145-0812-->

The designation of Rigel as β Orionis (Beta Orionis) was made by [[Johann Bayer]] in 1603. The "beta" designation is commonly given to the second-brightest star in each constellation, but Rigel is almost always brighter than α Orionis ([[Betelgeuse]]).<ref name="schaaf"/> Astronomer [[James B. Kaler]] has speculated that Rigel was designated by Bayer during a rare period when it was outshone by the variable star Betelgeuse, resulting in the latter star being designated "alpha" and Rigel designated "beta".<ref name="kalerrigel"/> Bayer did not strictly order the stars by brightness, instead grouping them by magnitude.<ref name=ridpath/> Rigel and Betelgeuse were both considered to be of the first magnitude class, and in Orion the stars of each class are thought to have been ordered north to south.<ref name=moore1996/> Rigel is included in the [[General Catalogue of Variable Stars]], but since it already has a [[Bayer designation]] it has no separate [[variable star designation]].<ref name=baa/>

Rigel has many other [[Stellar designations and names|stellar designations]] taken from various catalogs, including the [[Flamsteed designation]] 19{{spaces}}Orionis (19 Ori), the [[Bright Star Catalogue]] entry HR{{spaces}}1713, and the [[Henry Draper Catalogue]] number HD{{spaces}}34085. These designations frequently appear in the scientific literature,<ref name=msc/><ref name=schultz/><ref name=markova/> but rarely in popular writing.<ref name=garfinkle1997/><ref name=burnham/>

== Observation ==
[[File:RigelAandB.jpg|left|thumb|Rigel A and Rigel B as they appear in a small telescope]]
Rigel is an [[Variable star|intrinsic variable]] star with an [[apparent magnitude]] ranging from 0.05 to 0.18.<ref name=guinan/> It is typically the seventh-brightest star in the [[celestial sphere]], excluding the Sun, although occasionally fainter than Betelgeuse.<ref name=burnham/> It is fainter than [[Capella]], which may also vary slightly in brightness.<ref name=Samus2017/> Rigel appears slightly blue-white and has a [[B-V color]] index of −0.06.<ref name="csiro"/> It contrasts strongly with reddish Betelgeuse.<ref name=DK/>

[[Culmination|Culminating]] every year at midnight on 12 December, and at 9:00{{spaces}}pm on 24 January, Rigel is visible on winter evenings in the [[Northern Hemisphere]] and on summer evenings in the [[Southern Hemisphere]].<ref name="schaaf"/> In the Southern Hemisphere, Rigel is the first bright star of Orion visible as the constellation rises.<ref name=ellyard/> Correspondingly, it 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 (astronomy)|asterism]] that includes [[Aldebaran]], Capella, [[Pollux (star)|Pollux]], [[Procyon]], and [[Sirius]]. Rigel is a prominent [[List of stars for navigation#Equatorial stars|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]]).<ref name=kerigan/>

=== Spectroscopy ===

Rigel's [[Stellar classification#Modern classification|spectral type]] is a defining point of the classification sequence for supergiants.<ref name=morgan1978/><ref name=morgan1950/> The overall spectrum is typical for a [[Late-type star|late]] B class star, with strong [[absorption line]]s of the hydrogen [[Balmer series]] as well as neutral helium lines and some of heavier elements such as oxygen, calcium, and magnesium.<ref name=abetti/> The [[luminosity class]] for B8 stars is estimated from the strength and narrowness of the hydrogen spectral lines, and Rigel is assigned to the [[bright supergiant]] class Ia.<ref name=mkk/> Variations in the spectrum have resulted in the assignment of different classes to Rigel, such as B8 Ia, B8 Iab, and B8 Iae.<ref name=schultz/><ref name=bally/>

As early as 1888, the heliocentric [[radial velocity]] of Rigel, as estimated from the [[Doppler shift]]s of its spectral lines, was seen to vary. This was confirmed and interpreted at the time as being due to a spectroscopic companion with a period of about 22 days.<ref name=plaskett/> The radial velocity has since been measured to vary by about {{val|10|ul=km/s}} around a mean of {{val|21.5|u=km/s}}.<ref name=morrison/>

In 1933, the [[Hα]] line in Rigel's spectrum was seen to be unusually weak and shifted {{val|0.1|ul=nm}} towards shorter wavelengths, while there was a narrow [[emission line|emission spike]] about {{val|1.5|u=nm}} to the long wavelength side of the main absorption line.<ref name=struve/> This is now known as 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.<ref name=struve/>

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 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.<ref name=morrison/><!--cites five previous sentences--> The line profile changes are interpreted as variations in 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 [[coronal loop|looping structures]] arising from the [[photosphere]] and driven by magnetic fields.<ref name=israelian/>

=== Variability ===
[[File:RigelLightCurve.png|thumb|right|A [[light curve]] for Rigel, adapted from Moravveji ''et al.'' (2012)<ref name=apj2012_747_108/>]]
Rigel has been known to vary in brightness since at least 1930. The small amplitude of Rigel's brightness variation requires [[Photoelectric sensor|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 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.<ref name=guinan1985/>

From analysis of ''[[Hipparcos]]'' satellite photometry, Rigel is identified as belonging to the [[Alpha Cygni variable|Alpha Cygni]] class of variable stars,<ref name="waelkens 1998"/> defined as "non-radially pulsating supergiants of the Bep–AepIa spectral types".<ref name=Samus2017/> In those spectral types, 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<ref name=AAVSOvartyps/> or have [[quasi-period]]s.<ref name=vangenderen/> 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,<ref name=IBVS/> which showed variations with a photographic amplitude of 0.039 magnitudes and a possible period of 2.075 days.<ref name=lefevre/> Rigel was observed with the Canadian [[Microvariability and Oscillations of STars telescope|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.<ref name=apj2012_747_108/>
{{clear left}}

=== Mass loss ===

From observations of the variable Hα spectral line, Rigel's mass-loss rate due to stellar wind is estimated be {{val|1.5|0.4|e=−7}} solar masses per year ({{solar mass|link=n}}/yr)—about ten million times more than the mass-loss rate from the [[Sun]].<ref name=chesneau2010/> More detailed optical and [[K band (infrared)|K{{nbsp}}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 the wind. Calculations of mass loss from the Hγ line give {{val|9.4|0.9|e=−7|u={{solar mass}}/yr}} in 2006-7 and {{val|7.6|1.1|e=−7|u={{solar mass}}/yr}} in 2009–10. Calculations using the Hα line give lower results, around {{val|1.5|e=−7|u={{solar mass}}/yr}}. The terminal wind velocity is {{val|300|u=km/s}}.<ref name=chesneau2014/> It is estimated that Rigel has lost about three solar masses ({{solar mass}}) since beginning life as a star of {{val|24|3|u={{solar mass}}}} seven to nine million years ago.<ref name=aaa445_3_1099/>

== Distance ==
[[File:Treasures3.jpg|thumb|right|alt=A very bright blue-white star with fainter stars near a sharply defined strip of nebulosity|Rigel and [[reflection nebula]] [[IC 2118]] in [[Eridanus (constellation)|Eridanus]]. Rigel B is not visible in the glare of the main star.]]

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.<ref name=v23n06/> The 2007 [[Hipparcos new reduction]] of Rigel's [[stellar parallax|parallax]] is {{val|3.78|0.34|ul=mas}}, giving a distance of {{convert|863|ly|pc|abbr=off}} with a [[margin of error]] of about 9%.<ref name=aaa474_2_653/> Rigel B, usually considered to be physically associated with Rigel and at the same distance, has a [[Gaia Data Release 3]] parallax of {{val|3.2352|0.0553|u=mas}}, suggesting a distance around {{convert|310|pc|ly|abbr=off|order=flip}}. However, the measurements for this object may be unreliable.<ref name=Gaia3/>

Indirect distance estimation methods have also been employed. For example, Rigel 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),<ref name=Guieu2010/><ref name="Jedicke1992"/> located at an [[angular separation]] of 2.5° from the star,<ref name=Guieu2010/> or a projected distance of {{convert|12|pc|ly|abbr=off|order=flip}} away.<ref name="kalerrigel"/> From measures of other nebula-embedded stars, IC{{spaces}}2118's distance is estimated to be {{convert|291|±|2|pc|ly|0|abbr=off|order=flip}}.<ref name=Kounkel2018/>

Rigel is an outlying member of the [[Orion OB1 association]], which is located at a distance of up to {{convert|500|pc|ly|abbr=off|order=flip}} from Earth. It is a member of the loosely defined [[Taurus-Orion R1 Association]], somewhat closer at {{convert|360|pc|ly|abbr=off|order=flip}}.<ref name=markova/><ref name=racine/> 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 is a [[runaway star]] with a complex history and might have originally formed in the main body of the association.<ref name=bally/>

== Stellar system ==

<div style="float:right; width:240px; border:solid black 1px; text-align: center; margin: 8px; padding: 4px; font-size: 90%;">
{{tree chart/start}}
{{tree chart|border=1| |, |S1| |S1='''Rigel''' }}
{{tree chart|border=0| |! |PA|PA=Separation = 9.5″{{break}}Period = 24,000{{spaces}}y }}
{{tree chart|border=1|-|( | |, |- |S2|S2='''Ba''' }}
{{tree chart|border=0| |! |, |( |PB|PB=Separation = {{val|0.58|u=mas}}{{break}}Period = {{Val|9.860|u=days}} }}
{{tree chart|border=1| |! |! |` |- |S3|S3='''Bb''' }}
{{tree chart|border=0| |` |( |PC|PC=Separation = {{Val|0.1|u=arcsecond}}{{break}}Period = 63{{spaces}}y }}
{{tree chart|border=1| | |` |S4| |S4='''C''' }}
{{tree chart/end}}
[[Star systems#Designations and nomenclature|Hierarchical scheme]] for Rigel's components<ref name=msc/>
<!--This hierarchy structure separates stars into subsystems which are assumed to be gravitationally attached. As some stars in the Rigel system have little evidence of orbital motion, which is questioned by some astronomers, we cannot say it is a "hierarchy of orbits".-->
</div>

The [[multiple star system|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 double star|visual companion]], which is likely a close triple-star system. A fainter star at a wider separation might be 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,<ref name="Herschel1782"/> usually abbreviated to H{{spaces}}II{{spaces}}33, or as H{{spaces}}2{{spaces}}33 in the Washington Double Star Catalogue.<ref name="WDS"/> [[Friedrich Georg Wilhelm von Struve]] first measured the relative position of the companion in 1822, cataloguing the visual pair as Σ 668.<ref name=FGWStruve/><ref name="Webb1917"/> 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°.<ref name="WDS"/><ref name=bakich/> 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 a challenging target for telescope apertures smaller than {{convert|15|cm|in|abbr=on|sigfig=1}}.<ref name=sanford/>

At Rigel's estimated distance, Rigel B's [[projected separation]] from Rigel A is over 2,200{{spaces}}[[astronomical unit]]s (AU). Since its discovery, there has been no sign of orbital motion, although both stars share a similar [[proper motion|common proper motion]].<ref name="Jedicke1992" /><ref name=sb9/> The pair would have an estimated orbital period of 24,000{{spaces}}years.<ref name=msc/> Gaia Data Release 3{{nbsp}}(DR3) contains a probably unreliable parallax for Rigel B, placing it at about {{convert|309|pc|ly|abbr=off|order=flip}}, further away than the Hipparcos distance for Rigel, but similar to the Taurus-Orion R1 association. There is no parallax for Rigel in Gaia DR3. The Gaia DR3 proper motions for Rigel B and the Hipparcos proper motions for Rigel are both small, although not quite the same.<ref name="Gaia3"/>

In 1871, [[Sherburne Wesley Burnham]] suspected Rigel B to be a binary system, and in 1878, he resolved it into two components.<ref name="burnham1900"/> This visual companion is designated as component C (Rigel C), with a measured separation from component B that varies from less than {{val|0.1|u="}} to around {{val|0.3|u="}}.<ref name=WDS/><ref name="burnham1900"/> In 2009, [[speckle interferometric|speckle interferometry]] showed the two almost identical components separated by {{val|0.124|u="}},<ref name=mason/> with visual magnitudes of 7.5 and 7.6, respectively.<ref name=WDS/> Their estimated orbital period is 63{{spaces}}years.<ref name=msc/> Burnham listed the Rigel multiple system as β{{spaces}}555 in his [[Burnham Double Star Catalogue|double star catalog]]<ref name="burnham1900"/> or BU{{spaces}}555 in modern use.<ref name=WDS/>

Component B is a double-lined [[spectroscopic binary]] system, which shows two sets of [[spectral line]]s combined within its single [[stellar spectrum]]. Periodic changes observed in relative positions of these lines indicate an orbital period of 9.86{{spaces}}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 the close visual component Rigel C, is likely a physical triple-star system,<ref name=sb9/> although Rigel C cannot be detected in the spectrum, which is inconsistent with its observed brightness.<ref name=sanford/>

In 1878, Burnham found another possibly associated star of approximately 13th magnitude. He listed it as component D of β{{spaces}}555,<ref name="burnham1900"/> although it is unclear whether it is physically related or a coincidental alignment. Its 2017 separation from Rigel was {{val|44.5|ul="}}, almost due north at a position angle of 1°.<ref name=WDS/> Gaia DR2 finds it to be a 12th magnitude sunlike star<!--Does "orange dwarf" count as "sunlike"?--> at approximately the same distance as Rigel.<ref name=dr2d/> 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.<ref name="kalerrigel"/>

A spectroscopic companion to Rigel was reported on the basis of radial velocity variations, and its orbit was even calculated, but subsequent work suggests the star does not exist and that observed pulsations are intrinsic to Rigel itself.<ref name=sb9/>

== Physical characteristics ==
[[File:Hertzsprung-Russell_Diagram_-_ESO_with_Rigel.png|thumb|right|upright=1.2|alt=A chart showing several labelled stars against shaded colored areas with axes of spectral type and absolute magnitude, and Rigel labelled near the top|Rigel's place at top-center on the [[Hertzsprung–Russell diagram]]]]

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]].<ref name=guinan/><ref name=seeds/> When it was on the main sequence, its [[effective temperature]] would have been around {{val|30,000|fmt=commas|ul=K}}.<ref name=saio/> Rigel's complex variability at [[Electromagnetic spectrum|visual wavelengths]] 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.<ref name=apj2012_747_108/>

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 the Sun. As such, their characteristics are mainly estimated from theoretical [[Stellar evolution#Models|stellar evolution models]].<ref name=demarque2008/> Its effective temperature can be estimated from the spectral type and color to be around {{val|12,100|fmt=commas|ul=K}}.<ref name=przybilla/> A mass of {{val|21|3|u=solar mass}} at an age of {{val|8|1}}{{nbsp}}million years has been estimated by comparing evolutionary tracks, while atmospheric modeling from the spectrum gives a mass of {{solar mass|{{val|24|8}}}}.<ref name=aaa445_3_1099/>

Although Rigel is often considered the most luminous star within 1,000 light-years of the Sun,<ref name="schaaf" /><ref name=burnham/> its energy output is poorly known. Using the Hipparcos distance of {{convert|264|pc|ly|abbr=off|order=flip}}, the estimated relative luminosity for Rigel is about 120,000 times that of the Sun ({{solar luminosity|link=y}}),<ref name=apj2012_747_108/> but another distance of {{convert|360|±|40|pc|ly|abbr=off|order=flip}} suggests an even higher luminosity of {{solar luminosity|219,000}}.<ref name=aaa445_3_1099/> Other calculations based on theoretical stellar evolutionary models of Rigel's atmosphere give luminosities anywhere between {{solar luminosity|83,000}} and {{solar luminosity|363,000}},<ref name=markova/> while summing the [[spectral energy distribution]] from historical photometry with the Hipparcos distance suggests a luminosity as low as {{val|61515|11486|u={{solar luminosity}}|fmt=commas}}.<ref name=baines/> A 2018 study using the [[Navy Precision Optical Interferometer]] measured the [[angular diameter]] as {{val|2.526|u=mas}}. After correcting for [[limb darkening]], the angular diameter is found to be {{val|2.606|0.009|u=mas}}, yielding a radius of {{solar radius|{{val|74.1|+6.1|-7.3}}|link=y}}.<ref name=baines/> An older measurement of the angular diameter gives {{val|2.75|0.01|u=mas}},<ref name=auf/> equivalent to a radius of {{solar radius|78.9}} at {{val|264|u=pc}}.<ref name=apj2012_747_108/> These radii are calculated assuming the Hipparcos distance of {{val|264|u=pc}}; adopting a distance of {{val|360|u=pc}} leads to a significantly larger size.<ref name=chesneau2014/> Older distance estimates were mostly far lower than modern estimates, leading to lower radius estimates; a 1922 estimate by [[John Stanley Plaskett]] gave Rigel a diameter of 25 million miles, or approximately {{Solar radius|28.9}}, smaller than its neighbor [[Aldebaran]].<ref name=plasket1922/>

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 star]]s that are three to four times as massive as the Sun.<ref name=msc/>

== Evolution ==

[[Stellar evolution]] models suggest 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.<ref name=saio/>

Rigel is likely to be [[Triple-alpha process|fusing helium]] in its core.<ref name=apj2012_749_74 /> 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 the [[Paul Ledoux#Ledoux criterion|Ledoux Criteria]].<ref name=saio/>

Rigel is expected to eventually end its stellar life as a [[Type II supernova]].<ref name=apj2012_749_74/> It is one of the closest known potential [[supernova]] progenitors to Earth,<ref name=apj2012_747_108/> and would be expected to have a maximum apparent magnitude of around {{val|-11}} (about the same brightness as a quarter Moon or around 300 times brighter than Venus ever gets).<ref name=guinan/> The supernova would leave behind either a black hole or a neutron star.<ref name=apj2012_749_74/>

== Etymology and cultural significance ==
[[File:Book of the Fixed Stars Auv0333 Orion.jpg|thumb|alt=Medieval illustration showing the stars of Orion overlaid with an image of a warrior|Orion illustrated in a copy of [[Abd al-Rahman al-Sufi]]'s ''[[Book of Fixed Stars]]''. The foot on the left is annotated ''rijl al-jauza al-yusra'', the Arabic name from which ''Rigel'' is derived.{{efn|1=Al-Sufi's book was translated into Latin and other European languages. Al-Sufi himself planned the figures, two for each constellation: one shows how they appear to an observer looking up toward the heavens; the other how they appear to the observer looking down upon a celestial globe.<ref name=ck2018/>}} ]]

The earliest known recording of the name ''Rigel'' is in the ''[[Alfonsine tables]]'' of 1521. It is derived from the Arabic name ''{{Transliteration|ar|Rijl Jauzah al Yusrā}}'', "the left leg (foot) of Jauzah" (i.e. ''rijl'' meaning "leg, foot"),<ref name=allen/> which can be traced to the 10th century.<ref name="KUNITZSCH1959"/> "Jauzah" was a proper name for Orion; an alternative Arabic name was {{lang|ar|رجل الجبار}} ''{{Transliteration|ar|rijl al-jabbār}}'', "the foot of 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.''{{efn|1=lit."... and it is called Algebar. It is also named Rigel."}}<ref name=Kunitzsch86/> 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]].<ref name="allen"/>

With the constellation representing the mythological Greek huntsman [[Orion (mythology)|Orion]], Rigel is his knee or (as its name suggests) foot; with the nearby star [[Beta Eridani]] marking Orion's footstool.<ref name="schaaf"/> Rigel is presumably the star known as "[[Aurvandil]]'s toe" in [[Norse mythology]].<ref name=cleasby/> 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 a cutlass by the maiden ''Bįhi'' (Sirius).<ref name=taylor/> The [[Lacandon people]] of southern Mexico knew it as ''tunsel'' ("little woodpecker").<ref name=milbraith/>

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.<ref name=mudrooroo/> The indigenous [[Wergaia|Boorong]] people of northwestern Victoria named Rigel as ''Collowgullouric Warepil''.<ref name=hamacher/> The [[Wardaman people]] of northern Australia know Rigel as the Red [[Kangaroo]] Leader ''Unumburrgu'' and chief conductor of ceremonies in a songline when Orion is high in the sky. [[Eridanus (constellation)|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.<ref name=harney/>

The [[Māori people]] of New Zealand named Rigel as ''[[Puanga]]'', said to be a daughter of ''Rehua'' ([[Antares]]), the chief of all stars.<ref name=parker/> 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.<ref name="kelley"/> ''Puaka'' is a [[Māori language#South Island dialects|southern name variant]] used in the South Island.<ref name="Best22"/>

In Japan, the Minamoto or [[Genji clan]] chose Rigel and its white color as its symbol, calling the star ''Genji-boshi'' ({{lang|ja|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]].<ref name="RENSHAW1"/><ref name=daijirin/><ref name=hojiri/>

== In modern culture ==

The [[MS Rigel|MS ''Rigel'']] 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.<ref name=minnehallen/> Two US Navy ships have borne the name [[USS Rigel|USS ''Rigel'']].<ref name=silverstone1968/><ref name=history/><ref name=navymil/> The [[SSM-N-6 Rigel]] was a [[cruise missile]] program for the [[US Navy]] that was cancelled in 1953 before reaching deployment.<ref name=yenne/>

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 was used as an [[astrofix]].<ref name=skerries/> [[Mount Rigel]], elevation {{convert|1910|m|ft|abbr=on}}, is also in Antarctica.<ref name=mountrigel/>{{clear}}

== See also ==
* [[Orion in Chinese astronomy]]

== Notes ==

{{notelist}}

== References ==

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<ref name=FGWStruve>{{cite book|first=Friedrich Georg Wilhelm|last=Struve|title=Catalogus novus stellarum duplicium et multiplicium maxima ex parte in Specula Universitatis Caesareae Dorpatensis per magnum telescopium achromaticum Fraunhoferi detectarum|url=https://books.google.com/books?id=sPjmAAAAMAAJ|year=1827|publisher=J.C. Schuenmann|location=Dorpati Livonorum}}</ref>

<ref name=CCDM>{{cite journal|bibcode=1994CoORB.115....1D|title=Catalogue des composantes d'etoiles doubles et multiples (CCDM) premiere edition – Catalogue of the components of double and multiple stars (CCDM) first edition|last1=Dommanget|first1=J.|last2=Nys|first2=O.|journal=Communications de l'Observatoire Royal de Belgique|volume=115|pages=1|year=1994}}</ref>

<ref name=ridpath>{{cite book|first=Ian|last=Ridpath|title=Star Tales|chapter=Bayer's ''Uranometria'' and Bayer letters |publisher=Lutterworth Press|location=Cambridge, United Kingdom|year=1989|isbn=978-0-7188-2695-6|chapter-url=http://www.ianridpath.com/startales/bayer.html}}</ref>

<ref name=moore1996>{{cite book|first=Patrick|last=Moore|title=Brilliant Stars|url=https://books.google.com/books?id=uWEOGwAACAAJ|year=1996|publisher=Cassell|location=London|isbn=978-0-304-34903-6}}</ref>

<ref name=ck2018>{{cite book|editor-last1=Casagrande-Kim|editor-first1=Roberta|editor-last2=Thrope|editor-first2=Samuel|editor-last3=Ukeles|editor-first3=Raquel|title=Romance and Reason: Islamic Transformations of the Classical Past|chapter=Mathematics, Astronomy, and Astrology|last1=Langermann|first1=Y. Tzvi|chapter-url=https://books.google.com/books?id=5fJIDwAAQBAJ&pg=PA92|year=2018|publisher=Princeton University Press|location=Princeton, New Jersey|isbn=978-0-691-18184-4|pages=92–93}}</ref>

}}

== External links ==

{{Commons category|Rigel}}
* {{APOD|date=15 January 2018|title=Rigel and the Witch Head Nebula}}
* {{APOD|date=16 November 2015|title=A Blazing Fireball between the Orion Nebula and Rigel}}
* [http://assa.saao.ac.za/sections/deep-sky/double-stars/news-and-articles/december-double-star-of-the-month-beta-orionis/ December double star of the month{{snd}}beta Orionis] Astronomical Society of Southern Africa
* [https://www.aavso.org/my-favorite-double-star My Favorite Double Star] AAVSO

{{Stars of Orion}}
{{Portal bar|Astronomy|Stars|Outer space}}
{{Sky|05|14|32.272|-|08|12|05.91|800}}

{{featured article}}

<!--Physical properties-->

[[Category:B-type supergiants]]
[[Category:B-type main-sequence stars]]
[[Category:Alpha Cygni variables]]
[[Category:Multiple star systems|4]]
[[Category:Population I stars]]
<!--Nomenclature/Catalogues-->
[[Category:Orion (constellation)]]
[[Category:Arabic words and phrases]]
[[Category:Bayer objects|Orionis, Beta]]
[[Category:Durchmusterung objects|BD-08 1063]]
[[Category:Flamsteed objects|Orionis, 19]]
[[Category:Henry Draper Catalogue objects|034085]]
[[Category:Hipparcos objects|024436]]
[[Category:Stars with proper names|Rigel]]
[[Category:Lucidae]]
[[Category:Brightest stars]]