Permanent object 32 identifies Alnilam, Epsilon Orionis, HD 37128 and HIP 26311. The International Astronomical Union applies the proper name to this star; the traditional Arabic name is commonly translated as the string or arrangement of pearls. SIMBAD classifies it B0 Ia, the notation for a very hot, luminous blue supergiant. Source: [SIMBAD, Alnilam](https://simbad.u-strasbg.fr/simbad/sim-basic?Ident=Alnilam). The “epsilon” Bayer letter is a historical label, not a statement that this central Belt star is fifth in physical size or distance.
A multiwavelength analysis combined optical, ultraviolet and X-ray observations because no one spectral band diagnoses the whole atmosphere. The ultraviolet resonance lines sample the accelerating outflow; optical hydrogen and helium lines constrain the photosphere and denser wind; X-ray emission lines trace shock-heated parcels embedded in much cooler gas. The study found that a smooth wind could not reproduce all diagnostics consistently. Small-scale clumping changes density-squared emission, so the inferred mass-loss rate falls when clumping is included. Source: [Puebla et al., *Monthly Notices of the Royal Astronomical Society* 456, 2907](https://academic.oup.com/mnras/article/456/3/2907/1089938).
That analysis also illustrates a central uncertainty. Published distance estimates then clustered near 400 parsecs, while the revised Hipparcos value was about 606 parsecs. Luminosity scales with the square of adopted distance, the modelled radius changes with it, and several wind diagnostics make mass-loss scale as distance or approximately distance to the three-halves power. A precise-looking luminosity or mass-loss number can therefore inherit a large distance assumption. Spectral type and the existence of a powerful structured wind are more robust than any single advertised radius or luminosity.
The wind is variable as well as clumped. Ultraviolet absorption changes with time, and optical line profiles do not repeat as a perfectly stable shell. X-rays are consistent with shocks distributed through the accelerating wind rather than a solid hot corona. “Blue supergiant” describes an evolutionary and atmospheric state; it does not mean the visible surface is blue gas flowing as one uniform layer.
The stored position is approximately right ascension 5h 36m and declination −1° 12′. Alnilam culminates around 44° high from latitude 45° N and 56° from 35° S. These geometric altitudes omit the calendar's hour, Moon, weather and local horizon.
To find Alnilam, identify Orion's unmistakable line of three nearly evenly spaced Belt stars. Alnilam is the central one, between Mintaka to the west and Alnitak to the east. Confirm the full three-star line rather than choosing the brightest nearby point. HIP 26311 is present in the repository's accepted Orion and Belt geometry, but the rendered finder and reader link remain unchecked.
At visual magnitude about 1.69, Alnilam is easy without optical aid. Source: [Sky & Telescope observing profile](https://skyandtelescope.org/stargazing-and-observing/celestial-objects-to-watch/bright-stars/meet-alnilam-orions-belt-buckle/). Binoculars make the Belt's spacing and surrounding field clearer; ordinary telescopes still show Alnilam as a brilliant stellar point, not a resolved supergiant disk or visible wind. Slight brightness and spectral variations require calibrated time-series measurements, while mass loss and X-ray shocks require spectroscopy and space observatories. Record field identification separately from any claim of variability, and leave changing weekly sky conditions to the calendar.
