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Bellatrix
Location of γ Orionis (circled)
Observation data
Epoch J2000      Equinox J2000
Constellation Orion
Pronunciation /ˈbɛlətrɪks/ /bɛˈleɪtrɪks/[1]
Right ascension 05h 25m 07.86325s[2]
Declination +06° 20′ 58.9318″[2]
Apparent magnitude (V) 1.64[3] (1.59 - 1.64[4])
Characteristics
Spectral type B2III[5] or B2V[6]
U−B color index −0.86[3]
B−V color index −0.21[3]
Variable type Suspected[4]
Astrometry
Radial velocity (Rv)+18.2[7] km/s
Proper motion (μ) RA: −8.11[2] mas/yr
Dec.: −12.88[2] mas/yr
Parallax (π)12.92±0.52 mas[2]
Distance250 ± 10 ly
(77 ± 3 pc)
Absolute magnitude (MV)−2.78[8]
Details
Mass8.40±0.10[6] M☉
Radius6.4[9] R☉
Luminosity4467[6] L☉
Surface gravity (log g)3.60[10] cgs
Temperature21700±500[6] K
Metallicity [Fe/H]−0.07[11] dex
Rotational velocity (v sin i)53.9±0.8[12] km/s
Age16.2[6] Myr
Other designations
Bellatrix, Al Najīd[13], Amazon Star[13], γ Orionis, Gamma Ori, γ Ori, 24 Ori, NSV 1972, BD+06°919, FK5 201, HD 35468, HIP 25336, HR 1790, SAO 112740[14]
Database references
SIMBADdata

Bellatrix is the third-brightest star and a candidate binary star in the constellation of Orion, positioned 5° west of the red supergiant Betelgeuse (Alpha Orionis). It has the Bayer designation γ Orionis, which is Latinized to Gamma Orionis. With a slightly variable magnitude of around 1.6, it is typically the 25th-brightest star in the night sky. It is the closest major star in Orion at only 244.6 light-years from the Solar System.

Nomenclature

[edit]
Bellatrix is a bright star in the constellation of Orion (top right).

The traditional name Bellatrix is from the Latin bellātrix "female warrior". It first appeared in the works of Abu Ma'shar al-Balkhi and Johannes Hispalensis, where it originally referred to Capella, but was transferred to Gamma Orionis by the Vienna school of astronomers in the 15th century, and appeared in contemporary reprints of the Alfonsine tables.[15] In 2016, the International Astronomical Union organized a Working Group on Star Names (WGSN)[16] to catalog and standardize proper names for stars. The WGSN's first bulletin of July 2016[17] included a table of the first two batches of names approved by the WGSN; which included Bellatrix for this star. It is now so entered in the IAU Catalog of Star Names.[18] The designation of Bellatrix as γ Orionis (Latinized to Gamma Orionis) was made by Johann Bayer in 1603. The "gamma" designation is commonly given to the third-brightest star in each constellation.

Standard star

[edit]

Bellatrix has been used as both a photometric and spectral standard star, but both characteristics have been shown to be unreliable.

In 1963, Bellatrix was included with a set of bright stars used to define the UBV magnitude system. These are used for comparison with other stars to check for variability, and so by definition, the apparent magnitude of Bellatrix was set to 1.64.[19] However, when an all-sky photometry survey was carried out in 1988, this star was suspected to be variable. It was measured ranging in apparent magnitude from 1.59 to 1.64,[20] and appears to be a low amplitude, possibly irregular variable.[21]

Physical properties

[edit]
From left to right, the stars Bellatrix, the Sun, and Algol B

The spectral types for O and early B stars were defined more rigorously in 1971 and Bellatrix was used as a standard for the B2 III type.[5] The expected brightness of Bellatrix from this spectral type is about one magnitude brighter than calculated from its apparent magnitude and Hipparcos distance.[22] Analysis of the observed characteristics of the star indicate that it should be a B2 main sequence star, not the giant that it appears from its spectral type.[6] Close analysis of high resolution spectra suggest that it is a spectroscopic binary composed of two similar stars less luminous than a B2 giant.[23]

Bellatrix is a massive star with about 8.6 times the mass[24] and 6.4 times the radius of the Sun.[9] As a massive star, this star will evolve faster than the Sun, currently it has an estimated age of approximately 25 million years.[24] The hydrogen should be exhausted in seven million years, after that Bellatrix will expand and cool. It may end its life in a supernova.[25] The effective temperature of the outer envelope of this star is 22,000 K,[10] which is considerably hotter than the 5,772 K on the Sun. This high temperature gives this star the blue-white hue that occurs with B-type stars.[26] It shows a projected rotational velocity of around 52 km/s.[27]

Companions

[edit]

Bellatrix was thought to belong to the Orion OB1 association of stars that share a common motion through space, along with the stars of Orion's Belt: Alnitak (Zeta Orionis), Alnilam (Epsilon Orionis), and Mintaka (Delta Orionis). However, this is no longer believed to be the case, as Bellatrix is now known to be much closer than the rest of the group.[25] It is not known to have a stellar companion,[28] although researchers Maria-Fernanda Nieva and Norbert Przybilla raised the possibility it might be a spectroscopic binary.[23] A 2011 search for nearby companions failed to conclusively find any objects that share a proper motion with Bellatrix. Three nearby candidates were all found to be background stars.[29]

Some researchers suspected that Bellatrix was a member of the 32 Orionis group. They proposed that the 32 Ori group should instead be termed the Bellatrix Cluster on the basis that the sky position and distance of Bellatrix are similar to those of the 32 Ori group.[30] The proper motion of Bellatrix deviates significantly from the mean motion of the group, leaving its membership in question. However, it may be possible to reconcile membership if the divergent velocity is the result of an unseen companion. For example, a face-on orbit with a black hole companion orbiting ~100 AU from the star with a period measured in centuries could account for the discrepancy.[31]

Etymology and cultural significance

[edit]

Bellatrix was also called the Amazon Star, which Richard Hinckley Allen proposed came from a loose translation of the Arabic name Al Najīd, the Conqueror.[13] A c.1275 Arabic celestial globe records the name as المرزم "the lion".[32] Bellatrix is one of the four navigational stars in Orion that are used for celestial navigation.[33]

In the 17th century catalogue of stars in the Calendarium of Al Achsasi al Mouakket, this star was designated Menkib al Jauza al Aisr, which was translated into Latin as Humerus Sinister Gigantis (The Left Shoulder of the Giant).[34]

The Wardaman people of northern Australia know Bellatrix as Banjan, the sparkling pigment used in ceremonies conducted by Rigel the Red Kangaroo Leader in a songline when Orion is high in the sky. The other stars of Orion are his ceremonial tools and entourage. Betelgeuse is Ya-jungin "Owl Eyes Flicking", watching the ceremonies.[35]

To the Inuit, the appearance of Betelgeuse and Bellatrix high in the southern sky after sunset marked the beginning of spring and lengthening days in late February and early March. The two stars were known as Akuttujuuk "those (two) placed far apart", referring to the distance between them, mainly to people from North Baffin Island and Melville Peninsula.[36]

See also

[edit]

References

[edit]
[edit]
Revisions and contributorsEdit on WikipediaRead on Wikipedia

Bellatrix

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from Grokipedia
Bellatrix, designated Gamma Orionis (γ Ori), is a prominent star situated in the constellation Orion, where it marks the left shoulder of the celestial hunter. It ranks as the third-brightest star in Orion, after and , and is the 26th-brightest star in the night sky overall, exhibiting an apparent visual magnitude of 1.64. The name Bellatrix originates from Latin, translating to "female warrior" or "Amazon Star," a designation that has been in use since at least the early and reflects the star's association with martial themes in classical astronomy. As a massive evolved , Bellatrix has a mass of approximately 8.6 solar masses and a radius of about 6.4 solar radii, with a surface of 22,000 —nearly four times hotter than the Sun's 5,778 . This results in a bolometric around 7,400 times that of the Sun, classifying it as a B2 III giant in the Morgan-Keenan system, though it may still be fusing in its core like a main-sequence . Bellatrix is also a , showing irregular fluctuations of a few percent in brightness over an undetermined period, and its iron abundance is about 85% of the Sun's ([Fe/H] = -0.07), typical for B-type stars in the solar neighborhood. Positioned at a of 252 light-years from Earth (based on DR3 ), Bellatrix is a candidate with a companion, Gamma Orionis B, an M0-type of about 0.5 solar es located 178 arcseconds away—corresponding to a minimum separation of roughly 13,800 astronomical units. Surrounded by faint nebulosity from the , the did not form in the same molecular cloud as most of Orion's other bright , making it something of an interloper in the constellation. Given its high , Bellatrix is expected to evolve rapidly, potentially culminating in a explosion that could briefly outshine much of the .

Names and Designations

Etymology and Meaning

The name Bellatrix, applied to the star designated as γ Orionis, originates from Latin, where it means "female warrior" or "Amazon star," derived from the noun bellator ("warrior") combined with the feminine agent suffix -trix to denote a female agent of war. This etymology evokes imagery of strength and , aligning symbolically with the star's position on the left shoulder of Orion, the mythological hunter often depicted in a martial pose. The name was originally assigned in medieval astronomy to the star Capella (α Aurigae) but was transferred to γ Orionis in the late by astronomers of the school, appearing in the 1492 edition of the Alphonsine Tables and gaining wider use in subsequent European star catalogs. This adoption reinforced the warrior connotation, portraying the star as a fierce companion to Orion's heroic figure. In Arabic astronomy, the star bore the name Al Najīd, translating to "the conqueror" or "the leader," a designation that loosely parallels the Amazon warrior theme through its emphasis on dominance and prowess.

Historical and Official Nomenclature

In medieval Latin astronomy, Bellatrix was referred to as Humerus Sinister Gigantis, translating to "the left shoulder of the giant," reflecting its position in the constellation Orion as the hunter figure. This name derived from earlier Arabic designations such as Menkib al Jauza al Aisr, meaning the shoulder of the central one of the twins, adapted to describe Orion's form. The star received its Greek-letter designation as γ Orionis from in his 1603 star atlas Uranometria, where Bayer systematically assigned letters to stars based on brightness within each constellation, with gamma indicating the third-brightest in Orion. Shortly after, in John Flamsteed's 1725 Historia Coelestis Britannica, it was cataloged as 24 Orionis, using a numerical system ordered by within constellations. In the , Bellatrix entered major modern catalogs, including the Harvard Revised (HR) as HR 1790 and the Henry Draper (HD) as HD 35468, which classify by spectral characteristics and brightness. The (IAU) formally approved "Bellatrix" as the proper name for γ Orionis on June 30, 2016, through its Working Group on Star Names, adding it to the official IAU List of Star Names to standardize while honoring historical traditions. This approval, meaning "female warrior" in Latin, solidified its use in professional astronomy.

Cultural Interpretations

In , Bellatrix forms the left shoulder of Orion, the mighty hunter placed among the stars by after his death from a scorpion's sting sent by . Depictions of the constellation often position the star at Orion's upper left side, from which his arm extends to wield a club or shield against celestial beasts like Taurus the bull. This association underscores themes of martial prowess, aligning with the star's Latin name meaning "female warrior," evoking the fierce Amazon figures in ancient lore. Indigenous cultures have woven Bellatrix into their own celestial narratives. Among the Wardaman people of Australia's , the star is known as Banjan, symbolizing the sparkling pigment applied during ceremonies led by the ancestor, represented by . In , Bellatrix pairs with as Akuttujuuk—"those placed far apart"—marking Orion's shoulders and signaling the transition to spring and longer days in the sky. These interpretations highlight the star's role in cultural storytelling and environmental cues. Bellatrix has served practical purposes in navigation across traditions, particularly as a seasonal indicator within the Orion constellation. In Arab astronomy, it was called Al Najīd, "the Conqueror," or Al Murzim al Najīd, "the Roaring Conqueror," heralding the heliacal rising of Rigel and used by sailors like Ibn Mājid for determining position in the Indian Ocean. Polynesian voyagers incorporated Orion's stars, including Bellatrix, into their star compass for wayfinding, tracking seasonal migrations and swells during long Pacific voyages. In modern popular culture, Bellatrix gains contemporary resonance through J.K. Rowling's series, where the villainous witch draws her name from the star, embodying its warrior essence as a fierce, unyielding in the .

Observational Characteristics

Position and Visibility

Bellatrix, designated Gamma Orionis, occupies the equatorial coordinates 05ʰ 25ᵐ 08ˢ and +06° 21' in the J2000 epoch. This places it within the constellation Orion, where it marks the left shoulder of the celestial hunter in traditional asterisms. Alongside at the right shoulder, at the left foot, and the three aligned belt stars (, , and ), Bellatrix contributes to Orion's distinctive figure, which dominates the winter sky for northern observers. The star's position ensures broad accessibility for amateur astronomers, visible without optical aid from latitudes spanning approximately 85° N to 75° S under clear, . In the , Bellatrix rises prominently in the eastern during evening hours from through , reaching near the meridian for optimal viewing. Its blue-white hue, stemming from its hot surface temperature, gives it a striking contrast against Orion's reddish , enhancing the constellation's visual appeal to the unaided eye. As a indistinguishable in angular size from other distant , Bellatrix requires no telescopic resolution for , though its fixed position relative to seasonal patterns makes it a reliable marker for locating nearby deep-sky objects like the .

Brightness and Variability

Bellatrix exhibits an apparent visual magnitude ranging from 1.59 to 1.64, rendering it the 26th brightest in the night . This places it among the most prominent naked-eye , with its brightness sufficient to be visible even in moderately light-polluted areas. Within the constellation Orion, Bellatrix ranks as the third-brightest star, following and , contributing significantly to the constellation's distinctive outline. The star's variability was first suspected during an all-sky photometry survey conducted in 1988, leading to its classification as a (denoted as V* in astronomical catalogs). This designation reflects small but detectable fluctuations in brightness, with an amplitude of approximately 0.05 magnitudes observed over timescales of days to weeks. Such variations distinguish Bellatrix from traditionally fixed standard stars, impacting its use in precise photometric calibrations.

Stellar Classification

Spectral Type

Bellatrix is classified as a B2III giant in the Morgan-Keenan (MK) spectral system, as confirmed by a 2024 study establishing a revised grid of northern standards for B-type stars using high-resolution spectra. This classification reflects its status as a post-main-sequence giant, with the Roman numeral III denoting the class based on line strengths and ratios, such as those involving Si III, He I, and metallic ions. Previously, the luminosity class was debated, with some analyses favoring B2V (main-sequence) based on Strömgren photometry and earlier MK criteria. B-type stars like Bellatrix are hot, blue supergiants or giants defined by spectra dominated by neutral (He I) absorption lines, which strengthen toward cooler subtypes within the class, alongside weaker Balmer lines and emerging metallic features such as those from and magnesium. The B2 subtype specifically indicates a where He I lines are prominent but not overwhelming, with the absence of strong He II lines distinguishing it from hotter O types. Its iron abundance is about 70% solar ([Fe/H] ≈ −0.15), consistent with expectations for young, massive B stars formed in the solar neighborhood. Spectral observations of Bellatrix must account for its variability, which can subtly influence line profiles and strengths.

Role as a Standard Star

Bellatrix was adopted as one of the standard stars for the in 1963 by Harold L. Johnson, serving as a reference for calibrating the magnitudes of other stars in the ultraviolet, blue, and visual bands. This selection was part of a broader effort to establish reliable benchmarks for broad-band photometry, leveraging Bellatrix's prominence as a bright, accessible northern-hemisphere star during the mid-20th century. In the Morgan-Keenan (MK) classification system, Bellatrix was utilized as a spectral standard for the B2 IV subtype in the original 1943 atlas, and later adopted as a standard for B2 III in 1971, aiding astronomers in determining the classes, colors, and effective temperatures of other B-type stars through comparison of absorption line features. Its spectrum, characterized by strong Balmer lines and metallic lines typical of giants, provided a foundational reference in the original 1943 MK atlas. This role stemmed from its early classification, which positioned it as a key example for standardizing types within the system. However, Bellatrix's slight variability, with an apparent visual magnitude fluctuating between 1.59 and 1.64 (an of about 0.05 mag), has undermined its reliability as a photometric standard, prompting recommendations to use more stable alternatives for precise calibrations. This irregularity, likely due to pulsations or other surface activity common in massive B , highlights the challenges in selecting unchanging references among bright, early-type .

Physical Properties

Distance and Kinematics

Bellatrix is situated at a distance of approximately 243 light-years, or 74.5 parsecs, from the Solar System, based on the Gaia Data Release 3 parallax measurement of about 13.4 milliarcseconds. This value refines the earlier estimate from the Hipparcos mission of roughly 250 light-years (76.6 parsecs). The updated parallax reflects improved astrometric precision from Gaia's five-year observation baseline, confirming Bellatrix's position within the Orion constellation for contextual coordinate reference. The star's , as determined from DR3, is −8.11 milliarcseconds per year in and −12.88 milliarcseconds per year in . These components describe Bellatrix's transverse motion across the sky, with the total proper motion amounting to approximately 15.2 milliarcseconds per year. The corresponding transverse velocity is about 5.4 km/s, calculated using the standard relation Vt=4.74×μ×(d/1000)V_t = 4.74 \times \mu \times (d / 1000) km/s, where μ\mu is the total proper motion in mas/yr and dd is the distance in parsecs. Bellatrix has a of +17.3 km/s, indicating it is receding from the Sun, as measured in a comprehensive 2023 spectroscopic survey of bright stars. Integrating the and yields space velocity components (U, V, W) of approximately (−10.5, −5.2, +13.8) km/s relative to the local standard of rest, resulting in a total space velocity of around 18 km/s. These kinematics place Bellatrix on a galactic that carries it toward the direction of Cygnus, distinct from the Orion OB1 association to which other prominent Orion stars belong; its differing distance and velocity confirm it is not gravitationally bound to this group.

Fundamental Parameters

Bellatrix possesses a mass of approximately 8 solar masses (M☉), characteristic of massive O and B-type stars that drive rapid stellar evolution. Its radius measures approximately 6 solar radii (R☉), expanded beyond main-sequence proportions due to its advanced evolutionary stage as a giant. The bolometric luminosity stands at 7,100 solar luminosities (L☉), reflecting efficient nuclear fusion in its core and significant energy output across the spectrum. The of Bellatrix's surface is 22,339 K, derived from detailed spectral fitting of its absorption lines in the ultraviolet-optical-near-infrared range. This high temperature underscores its as a hot B2 III giant, with a dominated by ionized and metals. At an age of 25.2 million years, Bellatrix has completed much of its main-sequence lifetime for a star of its mass, fusing into in its core. It is projected to deplete its core supply and undergo post-main-sequence within the next 1–2 million years, expelling its outer layers and leaving behind a small, hot, dense core. Interferometric observations yield an of 0.72 milliarcseconds for Bellatrix, corrected for effects that reduce the apparent size at the edges. Scaling this measurement by its distance implies a physical consistent with the derived 6 R☉ value.

System Components

Primary Star

Bellatrix's primary star is classified as a B2III giant, a luminous that contributes the vast majority of the system's visible light and defines its overall spectrum. This classification stems from detailed spectroscopic analysis revealing strong and lines characteristic of hot, evolved massive stars. As the dominant component, it exhibits the system's of 1.64 and blue-white coloration, with an around 21,750 K supporting its spectral features. The star rotates rapidly, with a projected equatorial velocity of approximately 35 km/s, which induces a modest oblateness in its shape due to centrifugal effects distorting the stellar envelope. This rotation rate is typical for intermediate-mass B-type giants and influences line broadening in high-resolution spectra. While not among the fastest rotators in its class, the spin contributes to equatorial bulging estimated at a few percent of the stellar radius. The primary's atmosphere features robust stellar winds driven by on ionized metals. These winds manifest as extended envelopes detectable in UV spectra and contribute to the star's variability on short timescales. Such outflow is consistent with theoretical models for B giants, where line-driven mechanisms dominate mass ejection. With an initial mass estimated at 8–9 M⊙M_\odot, the primary qualifies as a for core collapse , expected to occur after core hydrogen exhaustion in roughly 10 million years. This evolutionary path follows standard models for massive stars, leading to iron core formation and explosive nucleosynthesis upon reaching the .

Suspected Companions

Bellatrix has no confirmed companions, either visual or spectroscopic, but potential wide visual companions are listed in the Washington Double Star Catalog (WDS). The entry WDS J05251+0621 includes several candidate pairs at separations of several arcseconds to arcminutes, but these are considered unbound due to significant differences in proper motions between Bellatrix and the proposed companions. The most notable is Gamma Orionis B, an M0-type of about 0.5 solar masses located 178 arcseconds away, corresponding to a minimum separation of roughly 13,800 AU; however, its differs, suggesting it is likely a line-of-sight coincidence rather than a bound companion. Three additional faint (20th magnitude) stars at separations of 6, 10, and 12 arcseconds are also probable unrelated field stars. Early observations of variations in Bellatrix raised suspicion of a , with possible wobbles but no determined or resolved secondary spectral lines. Hypotheses for an unseen companion, such as a low-mass star or like a , have been proposed to explain these variations, but they remain unconfirmed by observations after , which show no clear evidence of multiplicity. The primary star's is measured at +18.2 ± 0.8 km/s. Bellatrix may be associated with the 32 Orionis group, a young stellar aggregate at approximately 85 pc, as its aligns closely with the group's mean of 18.6 ± 0.3 km/s. Such membership would imply co-moving companions on scales of ~100 pc, shared with other group members through common Galactic motion. However, Bellatrix's distance (~77 pc or 250 light-years) and differing (μ_α cos δ = −8.11 mas/yr, μ_δ = −12.88 mas/yr) argue against firm inclusion, though its properties can be reconciled with membership if it is in a face-on perturbed by a distant companion (a ∼102 AU).

References

  1. http://stars.astro.illinois.edu/sow/bellatrix.html
  2. https://earthsky.org/brightest-stars/bellatrix-3rd-brightest-star-in-orion/
  3. https://skyandtelescope.org/observing/celestial-objects-to-watch/bright-stars/meet-bellatrix-the-amazon-star/
  4. https://www.universeguide.com/star/25336/bellatrix
  5. https://www.youtube.com/watch?v=on2-yUhyykA
  6. https://www.etymonline.com/word/Bellatrix
  7. https://www.merriam-webster.com/dictionary/Bellatrix
  8. https://theplanets.org/stars/bellatrix-star/
  9. https://www.britannica.com/place/Bellatrix
  10. https://www.constellationsofwords.com/bellatrix/
  11. https://in-the-sky.org/data/catalogue.php?cat=Flamsteed&view=1
  12. https://www.pas.rochester.edu/~emamajek/WGSN/WGSN_bulletin1.pdf
  13. https://earthsky.org/constellations/orion-the-hunter-most-recognizable/
  14. https://www.star-facts.com/bellatrix/
  15. https://www.starlab.com/wp-content/uploads/2017/04/D.-27.-Inuit-v616.pdf
  16. https://rutter-project.org/wp-content/uploads/2021/10/Stars_of_Arab_Navigation.pdf
  17. https://hokulea.com/polynesian-wayfinding/
  18. https://www.harrypotter.com/features/the-harry-potter-characters-named-after-constellations
  19. https://www.space.com/16659-constellation-orion.html
  20. https://www.constellation-guide.com/constellation-list/orion-constellation/
  21. https://www.skyatnightmagazine.com/advice/bellatrix
  22. https://astropixels.com/stars/Bellatrix-01.html
  23. http://simbad.u-strasbg.fr/simbad/sim-basic?Ident=Bellatrix
  24. https://www.aanda.org/articles/aa/pdf/2024/10/aa49298-24.pdf
  25. https://ned.ipac.caltech.edu/level5/ASS_Atlas/paper.pdf
  26. https://stardate.org/podcast/2025-04-13
  27. https://www.aanda.org/articles/aa/full_html/2014/02/aa22758-13/aa22758-13.html
  28. https://academic.oup.com/mnras/article/468/1/1198/3059985
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