Abstract: Tan Tian, translated from John Herschel’s Outlines of Astronomy during the late Qing dynasty, is considered as the first systematic work of Western modern astronomy translated and introduced into China. It’s the first time that Chinese astronomy attempted to achieve a theoretical transformation to an astronomy of modern times. The authors of this article have discovered in the Bibliothèque nationale de France an important edition of Tan Tian—previously recorded in bibliographies but never personally examined by domestic researchers. It turned out to be the first edition completed by the London Missionary Society Press in 1859, with an English preface written by one of its translators, Alexander Wylie, and the first edition of an English-Chinese vocabulary of astronomical terms. Apart from that, we also discovered a revised 1874 edition of Tan Tian at the National Library of Australia published by the Jiangnan Manufacturing Bureau, different from those preserved in China in that it has Alexander Wylie’s handwritten annotations on its cover, a feature absent in copies preserved in China. Based on these two relics overseas, this article compares these two translations with their original works respectively, quantifies the extent of omissions and adaptations made by the translators, examines how they conveyed the ideas of a modern Chinese astronomy, and analyzes the scholarly significance of this work. Our research concludes that the translation and editorial arrangement of Tan Tian reflects the translators’ understanding and induction of modern Western astronomy, and at the same time, integrates the translators' knowledge of and reflections on traditional Chinese astronomy. It is not just a simply a translation, but rather paradigmatic fusion of Chinese and Western astronomy and a seminal work initiating the westernization of Chinese astronomy.