Eta Orionis
Eta Orionis, Latinized from η Orionis, is a multiple star in the constellation Orion. It lies a little to the west of Orion's Belt between Delta Orionis and Rigel, being closer to Delta Orionis than to Rigel. It lies at a distance of around 1,000 light-years from Earth and is part of the Orion OB1 association. System Eta Orionis is listed in multiple star catalogues as having two companions: a bright component B less than 2″ away; and a faint component C nearly 2′ away. The two are estimated to orbit every 1,800 years. The primary star, Eta Orionis A, is itself a spectroscopic triple star, known from multiple spectral lines with varying radial velocities. The most distant component Ac, has been resolved using speckle interferometry, at a separation of about 0.04″. It orbits the other two in 9.4 years. The two closest stars, Aa and Ab, are separated by only about a tenth of an astronomical unit and orbit in just under eight days. The system lies within the Orion OB1 association, a group of massive stars that includes most of the bright stars of Orion. It is assigned to the oldest and closest part of the association, known