The identification of these three stars as a belt is a very old one. The Arabic names of two of the
stars reflect this: Mintaka means 'the belt' and
Alnitak means 'the girdle'. (The name of the third
star, Alnilam, means 'the string of pearls'.)
It has been suggested that the three Belt-stars influenced the placing of the Pyramids at Giza,
and it is certainly true that there is a remarkable correspondence of position between the Pyramids and the stars.
The linear alignment of the Belt is a line-of-sight effect that conceals somewhat the true relations of the stars
making it up. In fact, the stars at either end of the Belt, Alnitak
and Mintaka, are the closest together in space: Alnitak is a
little over 700 light years from Earth, and
Mintaka about forty light years closer. The central
star, Alnilam, is much more distant than either of these,
lying on the edge of the Orion Molecular Cloud nearly 2,000 light years from the
Solar System.
Alnilam is the most massive and luminous of the three
stars, so that despite its greater distance it still shines more brightly
than its two companions. If the three stars were the same distance away,
Alnilam would easily outshine the other Belt-stars. It is about
10,000 times more luminous than the Sun.
Nebulae
Like much of its parent constellation, Orion's Belt
is a highly nebulous region of the sky. This is especially true in the direction of Alnitak, where
numerous nebulous structures are found. The most famous of these is undoubtedly the
dark Horsehead Nebula, a dark cloud blotting out the light from the red-pink streak of IC 434.
Also occupying this region are the less well known Flaming Tree Nebula
(NGC 2024) and the so-called Lump Star (NGC 2023).
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