Bellatrix is the third-brightest

star A star is an astronomical object comprising a luminous spheroid of plasma (physics), plasma held together by its gravity. The List of nearest stars and brown dwarfs, nearest star to Earth is the Sun. Many other stars are visible to the naked ...

in the

constellation A constellation is an area on the celestial sphere in which a group of visible stars forms Asterism (astronomy), a perceived pattern or outline, typically representing an animal, mythological subject, or inanimate object. The origins of the e ...

of Orion, positioned 5° west of the red supergiant

Betelgeuse Betelgeuse is a red supergiant of spectral type M1-2 and one of the largest stars visible to the naked eye. It is usually the tenth-brightest star in the night sky and, after Rigel, the second-brightest in the constellation of Orion ...

(Alpha Orionis). It has the

Bayer designation A Bayer designation is a stellar designation in which a specific star is identified by a Greek or Latin letter followed by the genitive form of its parent constellation's Latin name. The original list of Bayer designations contained 1,564 stars. ...

γ Orionis, which is Latinized to Gamma Orionis. With a slightly

variable Variable may refer to: * Variable (computer science), a symbolic name associated with a value and whose associated value may be changed * Variable (mathematics), a symbol that represents a quantity in a mathematical expression, as used in many ...

magnitude of around 1.6, it is typically the 25th-brightest star in the

night sky The night sky is the nighttime appearance of celestial objects like stars, planets, and the Moon, which are visible in a clear sky between sunset and sunrise, when the Sun is below the horizon. Natural light sources in a night sky include ...

. Located at a distance of 250

light-years A light-year, alternatively spelled light year, is a large unit of length used to express astronomical distances and is equivalent to about 9.46 trillion kilometers (), or 5.88 trillion miles ().One trillion here is taken to be 1012 ...

from the Sun, it is a blue giant star around 7.7 times as massive as the sun with 5.75 times its diameter.

Nomenclature

The traditional name ''Bellatrix'' is from the

Latin Latin (, or , ) is a classical language belonging to the Italic branch of the Indo-European languages. Latin was originally a dialect spoken in the lower Tiber area (then known as Latium) around present-day Rome, but through the power of the ...

''bellātrix'' "female warrior"; it first appeared in the works of

Abu Ma'shar al-Balkhi Abu Ma'shar al-Balkhi, Latinized as Albumasar (also ''Albusar'', ''Albuxar''; full name ''Abū Maʿshar Jaʿfar ibn Muḥammad ibn ʿUmar al-Balkhī'' ; , AH 171–272), was an early Persian Muslim astrologer, thought to be the greatest ast ...

and

Johannes Hispalensis John of Seville (Latin: ''Johannes Hispalensis'' or ''Johannes Hispaniensis'') ( fl. 1133-53) was one of the main translators from Arabic into Castilian in partnership with Dominicus Gundissalinus during the early days of the Toledo School of Tran ...

, where it originally referred to

Capella Capella is the brightest star in the northern constellation of Auriga. It has the Bayer designation α Aurigae, which is Latinised to Alpha Aurigae and abbreviated Alpha Aur or α Aur. Capella is the sixth-brightest star i ...

, 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''. In 2016, the

International Astronomical Union The International Astronomical Union (IAU; french: link=yes, Union astronomique internationale, UAI) is a nongovernmental organisation with the objective of advancing astronomy in all aspects, including promoting astronomical research, outreac ...

organized a

Working Group on Star Names The International Astronomical Union (IAU) established a Working Group on Star Names (WGSN) in May 2016 to catalog and standardize proper names for stars for the international astronomical community. It operates under Division C – Education ...

(WGSN) to catalog and standardize proper names for stars. The WGSN's first bulletin of July 2016 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. The designation of Bellatrix as γ Orionis ( Latinized to Gamma Orionis) was made by

Johann Bayer Johann Bayer (1572 – 7 March 1625) was a German lawyer and uranographer (celestial cartographer). He was born in Rain, Lower Bavaria, in 1572. At twenty, in 1592 he began his study of philosophy and law at the University of Ingolstadt, a ...

in 1603. The "gamma" designation is commonly given to the third-brightest star in each constellation

Standard star

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 Apparent magnitude () is a measure of the brightness of a star or other astronomical object observed from Earth. An object's apparent magnitude depends on its intrinsic luminosity, its distance from Earth, and any extinction of the object's li ...

of Bellatrix was set to 1.64. However, when an all-sky

photometry Photometry can refer to: * Photometry (optics), the science of measurement of visible light in terms of its perceived brightness to human vision * Photometry (astronomy), the measurement of the flux or intensity of an astronomical object's electrom ...

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, and appears to be a low amplitude, possibly irregular variable.

Physical properties

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. The expected brightness of Bellatrix from this spectral type is about one magnitude brighter than calculated from its apparent magnitude and Hipparcos distance. Analysis of the observed characteristics of the star indicate that it should be a B2

main sequence In astronomy, the main sequence is a continuous and distinctive band of stars that appears on plots of stellar color versus brightness. These color-magnitude plots are known as Hertzsprung–Russell diagrams after their co-developers, Ejnar Her ...

star, not the giant that it appears from its spectral type. Close analysis of high resolution spectra suggest that it is a spectroscopic binary composed of two similar stars less luminous than a B2 giant. Bellatrix is a massive star with about 7.7 times the mass and 5.8 times the radius of the Sun. It has an estimated age of approximately 25 million years—old enough for a star of this mass to consume the hydrogen at its core and begin to evolve away from the

into a

giant star A giant star is a star with substantially larger radius and luminosity than a main sequence, main-sequence (or ''dwarf'') star of the same effective temperature, surface temperature.Giant star, entry in ''Astronomy Encyclopedia'', ed. Patrick Moo ...

. The

effective temperature The effective temperature of a body such as a star or planet is the temperature of a black body that would emit the same total amount of electromagnetic radiation. Effective temperature is often used as an estimate of a body's surface temperature ...

of the outer envelope of this star is , which is considerably hotter than the 5,778 K on the Sun. This high temperature gives this star the blue-white hue that occurs with

B-type star A B-type main-sequence star (B V) is a main-sequence (hydrogen-burning) star of spectral type B and luminosity class V. These stars have from 2 to 16 times the mass of the Sun and surface temperatures between 10,000 and 30,000 K. B-type star ...

s. It shows a

projected rotational velocity Stellar rotation is the angular motion of a star about its axis. The rate of rotation can be measured from the spectrum of the star, or by timing the movements of active features on the surface. The rotation of a star produces an equatorial bulge ...

of around 52 km/s.

Companions

Bellatrix was thought to belong to the

Orion OB1 association Orion OB1 (Ori OB1) is a contingent group of several dozen hot giant stars of spectral types O and B in Orion. Associated are thousands of lower-mass stars, and a (smaller but significant) number of protostars. It is part of the larger Orion mo ...

of stars that share a common motion through space, along with the stars of

Orion's Belt Orion's Belt or the Belt of Orion, also known as the Three Kings or Three Sisters, is an asterism in the constellation Orion. It consists of the three bright stars Alnitak Alnitak is a triple star system in the constellation of ...

Alnitak Alnitak is a triple star system in the constellation of Orion. It has the designations ζ Orionis, which is Latinised to Zeta Orionis and abbreviated Zeta Ori or ζ Ori, and 50 Orionis, abbreviated 50 Ori. The system is located at a ...

(Zeta Orionis),

Alnilam Alnilam is the central star of Orion's Belt in the equatorial constellation of Orion. It has the Bayer designation ε Orionis, which is Latinised to Epsilon Orionis and abbreviated Epsilon Ori or ε Ori. This is a massive, blue supe ...

(Epsilon Orionis), and

Mintaka Mintaka , designation Delta Orionis (δ Orionis, abbreviated Delta Ori, δ Ori) and 34 Orionis (34 Ori), is a multiple star system some 1,200 light-years from the Sun in the constellation of Orion. Together with Alnitak (Zeta Orio ...

(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. It is not known to have a stellar companion, although researchers Maria-Fernanda Nieva and Norbert Przybilla raised the possibility it might be a spectroscopic binary. A 2011 search for nearby companions failed to conclusively find any objects that share a

proper motion Proper motion is the astrometric measure of the observed changes in the apparent places of stars or other celestial objects in the sky, as seen from the center of mass of the Solar System, compared to the abstract background of the more dista ...

with Bellatrix. Three nearby candidates were all found to be background stars. Some researchers suspected that Bellatrix was a member of 32 Orionis group. The 32 Ori group should 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. The

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 A black hole is a region of spacetime where gravitation, gravity is so strong that nothing, including light or other Electromagnetic radiation, electromagnetic waves, has enough energy to escape it. The theory of general relativity predicts t ...

companion orbiting from the star with a period measured in centuries could account for the discrepancy.

Etymology and cultural significance

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. A c.1275 Arabic celestial globe records the name as المرزم "the lion". Bellatrix is one of the four

navigational stars Fifty-seven navigational stars and additionally the star Polaris are given a special status in the field of celestial navigation. Of the approximately 6,000 stars visible to the naked eye under optimal conditions, these selected stars are ...

in Orion that are used for

celestial navigation Celestial navigation, also known as astronavigation, is the practice of position fixing using stars and other celestial bodies that enables a navigator to accurately determine their actual current physical position in space (or on the surface of ...

. In the 17th century catalogue of stars in the ''Calendarium'' of

Al Achsasi al Mouakket Muḥammad al-Akhṣāṣī al-Muwaqqit ( ar, محمد الاخصاصي الموقت) was an Egyptian astronomer whose and catalogue of stars, ('Pearls of brilliance upon the solar operations'), was written at Cairo about 1650. Al-Akhsasi was a s ...

, this star was designated ''Menkib al Jauza al Aisr'', which was translated into

as ''Humerus Sinister Gigantis''. The

Wardaman people The Wardaman people are a small group of Aboriginal Australians living about South-West of Katherine, on Menngen Aboriginal Land Trust in the Northern Territory of Australia. Language Wardaman is a non Pama-Nyungan language. Though close to ...

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. To the

Inuit Inuit (; iu, ᐃᓄᐃᑦ 'the people', singular: Inuk, , dual: Inuuk, ) are a group of culturally similar indigenous peoples inhabiting the Arctic and subarctic regions of Greenland, Labrador, Quebec, Nunavut, the Northwest Territories ...

, 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.

References

External links

Spectrum of Bellatrix
*

Navigational Stars Fifty-seven navigational stars and additionally the star Polaris are given a special status in the field of celestial navigation. Of the approximately 6,000 stars visible to the naked eye under optimal conditions, these selected stars are ...

{{DEFAULTSORT:Bellatrix B-type giants Suspected variables Orion (constellation) Orionis, Gamma 1790 Durchmusterung objects Orionis, 24 035468 025336 Stars with proper names