Alnilam
blue supergiant star
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 supergiant star some 1,250 light-years distant. It is estimated to be 270,000 times as luminous as the Sun, and 28 times as massive.
Observation
It is the 29th-brightest star in the sky (the fourth brightest in Orion) and is a blue supergiant. Together with Mintaka and Alnitak, the three stars make up Orion's Belt, known by many names across many ancient cultures. Alnilam is the middle star.
Since 1943, the spectrum of this star has served as one of the stable anchor points by which other stars are classified, for the spectral class B0Ia. Although the spectrum shows variations, particularly in the H-alpha absorption lines, this is considered typical for this type of luminous hot supergiant. It is also one of the 58 stars used in celestial navigation.
The public source identifies “Alnilam” as blue supergiant star. This brief keeps that definition visible, then builds a research path around Alnilam, blue and supergiant.
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Named sources, stable identifiers and responsible institutions provide the strongest route from overview to verifiable evidence. The source revision retrieved here is dated Sep 15, 2026. The linked authority identifier is Q13070. None of the 0 selected statements returned an explicit reference. The first chronological checks are 1943.
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This entry incorporates text from “Alnilam” on English Wikipedia. Contributors are listed in the page history. Text is available under the Creative Commons Attribution-ShareAlike 4.0 License. Selected authority identifiers and statements are retrieved from Wikidata under CC0; their references and qualifiers remain part of the verification path.