Arc star cluster
From Halopedia, the Halo wiki
The Arc star cluster is a cluster of stars in the Milky Way galaxy and likely within the Orion Arm, situated near to or within human space. The cluster contains the planet of Heian. At some time during 2544, UNSC satellite reconnaissance showed high-end magnetic and radar signatures in the cluster, leading to the commencement of Operation: GREY VEIL.