Bellatrix
Bellatrix is the female warrior star in Orion's shoulder.
Bellatrix, also designated Gamma Orionis, is the third-brightest star in the constellation Orion. It sits about 5° west of the red supergiant Betelgeuse. Its apparent magnitude hovers around 1.6 with slight variation, making it roughly the 25th-brightest star in Earth’s night sky. At a distance of 244.6 light-years, it is the nearest major star in Orion.
The name Bellatrix comes from the Latin for “female warrior.” It first appeared in the works of Abu Ma'shar al-Balkhi and Johannes Hispalensis, originally referring to Capella, but was reassigned to Gamma Orionis by the Vienna school of astronomers in the 15th century and later appeared in reprints of the Alfonsine tables. In 2016, the International Astronomical Union’s Working Group on Star Names officially approved Bellatrix for this star. Johann Bayer gave it the Bayer designation γ Orionis in 1603, as the gamma designation typically marks the third-brightest star in a constellation.
Bellatrix has served as both a photometric and spectral standard star, though both roles have proven unreliable. In 1963, it was included in a set of bright stars used to define the UBV magnitude system, with its apparent magnitude set to 1.64. However, an all-sky photometry survey in 1988 suggested it might be variable, with measurements ranging from 1.59 to 1.64, indicating a low-amplitude, possibly irregular variable.
The spectral types for O and early B stars were more rigorously defined in 1971, with Bellatrix used as a standard for the B2 III type. Its expected brightness from this spectral type is about one magnitude brighter than calculated from its apparent magnitude and Hipparcos distance. Analysis suggests it should be a B2 main-sequence star rather than the giant its spectral type implies. High-resolution spectra hint it might be a spectroscopic binary of two similar stars less luminous than a B2 giant, but interferometry confirms no such binary exists, setting an upper mass limit for any main-sequence companion.
Bellatrix is a massive star with about 8.4 times the Sun’s mass and 6.2 times its radius. It is roughly 28 million years old and will evolve faster than the Sun. Its hydrogen should be exhausted in about seven million years, after which it will expand and cool, possibly ending as a supernova.
Quick Facts
- Bayer designation
- γ Orionis (Gamma Orionis)
- Apparent magnitude
- ~1.6 (variable, ranging 1.59–1.64)
- Distance
- 244.6 light-years
- Age
- ~28 million years
Facts from the source article.
Lore & Background
The traditional name Bellatrix comes from the Latin bellātrix, meaning '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, appearing in contemporary reprints of the Alfonsine tables. In 2016, the International Astronomical Union's Working Group on Star Names approved Bellatrix for this star, and it is now entered in the IAU Catalog of Star Names. The Bayer designation γ Orionis was assigned by Johann Bayer in 1603.
Bellatrix has been used as both a photometric and spectral standard star, but both characteristics have been shown to be unreliable. In 1963 it was included in a set of bright stars defining the UBV magnitude system, with its apparent magnitude set to 1.64. However, an all-sky photometry survey in 1988 suspected it to be variable, measuring it ranging from 1.59 to 1.64, possibly an irregular variable. Its spectral type was used as a standard for B2 III in 1971, but analysis suggests it should be a B2 main sequence star, not a giant. Close analysis of high-resolution spectra raises the possibility it is a spectroscopic binary, though interferometry confirms it is not a binary of similar-brightness stars.
Bellatrix is a massive star with about 8.4 times the mass and 6.2 times the radius of the Sun. It has an estimated age of approximately 28 million years, and its hydrogen should be exhausted in seven million years, after which it will expand and cool, possibly ending in a supernova. It shows a projected rotational velocity of around 52 km/s. It was once thought to belong to the Orion OB1 association, but is now known to be much closer than the rest of the group. A 2011 search for nearby companions failed to find any objects sharing its proper motion; three candidates were all background stars. Some researchers proposed it might belong to the 32 Orionis group, but its proper motion deviates significantly from the group's mean motion, though membership could be reconciled if an unseen companion—possibly a black hole—accounts for the discrepancy.
Reader's Guide
Bellatrix holds significance as a navigational star, one of four in Orion used for celestial navigation. Its name and cultural roles span multiple traditions: it was called the Amazon Star, and a c.1275 Arabic celestial globe records the name 'the lion'. In the 17th-century Calendarium of Al Achsasi al Mouakket, it was designated Menkib al Jauza al Aisr, translated as 'The Left Shoulder of the Giant'. 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. 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, meaning 'those (two) placed far apart'. Its legacy as a standard star is complicated by its unreliable photometric and spectral characteristics, and its possible membership in stellar groups remains debated. Despite these uncertainties, Bellatrix remains a key reference point in Orion and a subject of ongoing study regarding its variability, binary nature, and evolutionary fate.
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