Orion's Sword is a compact asterism in the constellation Orion. It comprises three stars and M42, the Orion Nebula, which together are thought to resemble a sword or its scabbard. This group is south of the prominent asterism, Orion's Belt. Fables and old beliefs are in Europe dominated or widely influenced by those of the Greco-Roman narratives. Beyond Europe this grouping is quite widely referenced as a weapon just as the majority of cultures perceived Orion's standout asymmetrical "hourglass" of seven very bright stars as a human.
The Orion Nebula consists of one of the nearest, massive molecular clouds about 1,300 light years from the solar system. This makes the nebula potentially the closest HII region to Earth, a mass of hydrogen that has been ionized by nearby, hot, young stars. Regions like this are called stellar nurseries, nurturing the birth of multiple young stars such as the Orion Nebula Star Cluster. These are a hallmark of the asterism.
Main stars
42 Orionis, also called c Ori, is a B1V magnitude star in the northern half of the Orion nebula. Theta Orionis has a more central position in the nebula, and is actually composed of a multi-star system. Iota Orionis is one of the brightest in the collection, in the south of the Orion nebula. Iota Orionis is a spectroscopic binary system, with a variable magnitude of O9III.
Scientific studies
Given the scientific significance of M42, Orion's Sword is a popular spot for stellar and protostellar studies. Using the Hubble Space Telescope, O'dell et al. focused on identifying previously unseen features of the nebula, such as high-ionization shocks, compact sources, and protoplanetary disks. Some studies have focused on the sword region overall. Gomez & Leda found that less than half of the OB and Hα stars in this region are associated with well-defined stellar clusters. This positional similarity, as well as the high star formation rates and gas pressure in the nearby molecular cloud, confirms the previous notion that old, foreground OB stars triggered star formation in this cloud.
