Sigma Octanus system

Sigma Octanus is a system of planets in FLEETCOM Sector Three with over 17 million people on Sigma Octanus IV. The Keyes Loop and the Battle of Sigma Octanus IV occurred here in 2552. Master Chief and the Blue Team also found a strange Forerunner artifact in Côte d'Azur Museum of Natural History on Sigma Octanus IV while the Covenant tried to retrieve it.

Trivia
While there is in fact no actual star with the designation Sigma Octanus, there is one named Sigma Octantis, a slight spelling change, located 270 lightyears from Sol, which is the most southern of all visible stars in the sky. This would make it the furthest known UNSC colony, significantly further than Epsilon Indi, or even 23 Librae.