Of the astral sciences in early imperial China, tianwen 天文 (‘heavenly patterns’) was that principally devoted to the observation and interpretation of heavenly ‘anomalies’ (yi 異). As passed down through the written tradition, tianwen omenology is at once global and extremely insular in its scope. On the one hand, tianwen presents the sky as a mirror of the Empire, or ‘subcelestial realm’ (tianxia 天下), with any disturbance in even the most inaccessible parts of the one reflected back for all to see in the other. On the other hand, and for this very reason, the private practice of tianwen was repeatedly banned from 268 CE onward that the state might establish a monopoly on omenological literacy, restricting knowledge thereof to the imperial archives and capital observatory. Stepping out of the capital and the received tradition, the view on the ground is rather different. In this talk, I will present the eighth-century Xuanxiang Xiqin wuzhou zhan 玄象西秦五州占 (Omens of the Dark Signs for the Five Prefectures of the Western Qin), fragments of which preserved in seven paper manuscripts from the ninth century discovered in the Dunhuang cave library. These manuscripts are local copies of a multi-volume omen compendium that is, for its part, a local production and that treats the night sky as a reflection of the local region—the Hexi Corridor, leading from the Middle Kingdom into Central Asia. Of central interest in this talk will be the question of the interaction and tension between centre and periphery in the creation of local knowledge traditions, particularly as concerns the identification of ‘anomaly’.