From Halopedia, the Halo wiki
The Beta Eridani system is a planetary system located in the Eridanus constellation, 89 light-years away from the Sol system. The Forerunner Builders once maintained a presence in the system, leaving several pieces of technology behind on an unspecified world in the system. The system was home to the UNSC Navy's Beta Eridani Naval Training Range.
During the Human-Covenant War, shortly before the Fall of Reach in 2552, the Beta Eridani system was attacked by the Covenant's Fleet of Valiant Prudence, a scouting fleet led by Supreme Commander Rho 'Barutamee. The fleet was attracted to the system by a Luminary that detected the Forerunner artifacts within the system. Upon arriving in the system, UNSC Lieutenant Robinson called for the UNSC cadets to flee the system.
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