Uruk is the only other site apart from Babylon where all major categories of Babylonian astral science1 are represented in cuneiform tablets. Although the number of tablets from Uruk with astral science is small compared to Babylon, they are especially relevant for reconstructing the context, development and transmission of astral science during the 1st millennium BCE. This is because most tablets from Uruk were excavated scientifically, unlike those from Babylon. Hence we know, albeit to varying degrees of precision, at which locations and in which stratigraphical layers they were found2 – information that is essential for the present investigation.3 In Uruk, the full range of Babylonian astral science is best represented in the Late Seleucid library of the Rēš, temple of the skygod Anu. Since this library and the scholars associated with it have been the subject of detailed investigations,4 the focus is shifted here to libraries from the preceding Neo Babylonian, Achaemenid and Early Seleucid periods. Three libraries in Uruk that predate the Rēš have yielded tablets with astral science: the library of the Eanna temple, that of Anu-ikṣur and his family and that of Iqīšâ and his family, two private libraries located in the same house (fig. 1). While all three have been surveyed elsewhere in the literature, the present contribution attempts to trace the development and the transfer of Babylonian astral science in and between these libraries in more detail.