Together with Mintaka and Alnitak, the three stars make up Orion's Belt, known by many names across many ancient cultures.

[5] Although the spectrum shows variations, particular in the H-alpha absorption lines, this is considered typical for this type of luminous hot supergiant.

Searle and colleagues, using CMFGEN code to analyse the spectrum in 2008, calculated a luminosity of 537,000 L☉, an effective temperature of 27,500 ± 100 K and a radius of 32.4 ± 0.75 R☉.

[13] A more recent detailed analysis of Alnilam across multiple wavelength bands produced very high luminosity, radius, and mass estimates, assuming the distance of 606 parsecs suggested by the Hipparcos new reduction.

[2] Adopting the larger parallax from the original Hipparcos reduction gives a distance of 412 parsecs[14] and physical parameters more consistent with earlier publications.

Its stellar winds may reach up to 2,000 km/s, causing it to lose mass about 20 million times more rapidly than the Sun.

Related spellings are Alnihan and Alnitam:[17] all three variants are evidently mistakes in transliteration or copy errors, the first perhaps due to confusion with النيلم al-nilam 'the sapphire'.