From Halopedia, the Halo wiki
The Urs system, collectively known as the Urs–Fied–Joori system and designated CE-80-9012 by the Forerunners, is a triple star system, housing the primary star Urs, and the orbiting stars Fied and Joori. Urs is also orbited by a system of several planets, of which the Sangheili homeworld Sanghelios is the fourth. Sanghelios is located on the innermost edge of the Urs system's habitable zone. Formerly under Covenant control, the system fell under the auspices of the Sangheili after the splintering of the Covenant in the Great Schism.
In pre-Covenant Sangheili mythology, the largest sun Urs was the chief deity in the pantheon of ancient Sangheili gods. The lord Urs is the divine father of the demigod hero Kel 'Darsam. After adopting the Forerunners as their new gods, many old Sangheili myths faded away but were never forgotten. Even well after the Covenant ended, "Until we meet again in Urs' everlasting light" was still a traditional way to say goodbye.
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