When you look up at the night sky during winter, you might have noticed three stars, equidistant from one another in a row that shine brightly! These stars are the Orion’s Belt, which prominently appears in the night sky between October and March, and is part of the constellation ‘Orion the Hunter’.
Orion consists of three belt stars, Alnitak, Alnilam and Mintaka. The stars in this belt are massive, formed from large amounts of gas and dust. Usually, they burn through their fuel instantaneously and rapidly go through evolution. As they evolve, they get brighter and more massive. The stars in Orion’s Belt are in the same stage, hence they shine brightly and are aligned in the sky.
Now, this belt exists slightly below the celestial equator. It is one of the 15 equatorial constellations, which can be witnessed from anywhere on Planet Earth for at least part of the year. They peak highest when seen from locations near the equator. Hence, one of the asterisms can be utilised to find 0 degree (the equator).
The westernmost star of the belt is Alnitak, a triple star system. The primary star is a massive hot supergiant, located nearly 800 lightyears from Earth. This star is 20 times more massive than our Sun. Its blue colour comes from the surface temperature, reaching around 28,000K. The central star of the belt is Alnilam, which is over 2,000 lightyears away. Due to its temperature, it emits a blue-white hue, making it the most luminous among the three stars. While the easternmost star, Mintaka, is a binary star system, with two stars orbiting each other. This is located 900 lightyears away from Earth. However, Mintaka is the only star visible from both the Northern and Southern hemispheres. This is due to its proximity to the celestial equator. Whereas Altinak and Alnigam are best seen from the Northern hemisphere. All the stars are in the range of 5-10 million years old, which is relatively young when compared to the Sun.
Despite the stark differences in their distances, they originated within a similar region of the Milky Way, and are part of the same general stellar association. Hence, they appear to be aligned.
The region around Orion’s Belt consists of many bright and well-known deep sky objects. These objects are a fragment of the larger Orion Molecular Cloud Complex, a huge star-forming region that encompasses most of constellation Orion. The brightest among them is Orion Nebula (Messier 42). It is part of an asterism known as Orion’s Sword. Appearing between the three points of light, it is located 1,344 lightyears away. It is the closest region of massive star formation to the Sun.
The region around Orion’s Belt consists of many nebulae. Alnitak ionises the Flame Nebula (NGC 2024), which is an emission nebula located around 1,350 lightyears away. It makes the surroundings of the Orion’s Belt colourful. Other smaller reflection nebulae like the IC 423 and IC 426 appear near Alnilam and Mintaka.
In 1990, the stars of the Orion’s Belt were not visible from several parts of the Earth for many months. The disappearance was due to a dust cloud in the Milky Way that had blocked the light of these stars. Several scholars also believe that Orion’s Belt played a major role in the construction of some monuments.
For instance, the Pyramids of Giza in Egypt are assumed to be aligned with the stars of the Orion’s Belt. The Orion’s Belt is also a prominent prop in the 1997 Hollywood sci-fi comedy flick Men in Black.