Elias von Löwen (Crätschmair): An unrecognized pioneer of the research on optical libration of the Moon

Johannes Hevelius is credited with being the first astronomer to systematically describe the optical libration of the Moon in his Selenographia (1647) and to present a quantitative model of the phenomenon in De motu Lunae libratorio. . . (1654). However, from the correspondence that Hevelius conducted in 1650 with Elias von Löwen (Crätschmair) and his wife Maria Cunitia, it follows that the first model of optical libration of the Moon, allowing predict the changing position of lunar spots relative to the edge of the lunar disk, was developed by von Löwen. In this article I will compare the predictions of von Löwen’s and Hevelius’s models for the years 1650–51 and present a chronology of early research on libration supplemented with von Löwen’s account.