Chi¹ Orionis

Traditionally the shape of Orion the Hunter includes the form of Orion's great club raised above his head, represented by a string of fainter stars running northward from Betelgeuse to separate the Ecliptic constellations of Taurus and Gemini. At the tip of this 'club' lie the two northernmost naked-eye stars of Orion, designated Chi¹ and Chi² Orionis.

This shared Bayer designation recognises the historical connection and proximity of these stars in the sky, but in reality they are entirely unrelated to one another. Chi² is a brilliant but distant supergiant star, while Chi¹ is a dwarf star and a relatively near neighbour of the Sun, at a distance of some twenty-eight light years.

Chi¹ Orionis is similar to the Sun in many ways. Both are yellow dwarfs, and both share similar values for their mass and luminosity (with Chi¹ Orionis being marginally the more massive and luminous of the two).

Chi¹ Orionis differs markedly from the Sun, however, in having a binary companion, a tiny red dwarf star that orbits the main yellow star over a period of some fourteen years. This red dwarf's orbit carries it close to the yellow primary, but is highly eccentric in nature. In terms of the Solar System, it can approach as closely as the outer edge of the Asteroid Belt, and recede as far as the orbit of Saturn. The presence of this small red star means that Chi¹ Orionis is highly unlikely to possess any kind of stable planetary system.