Peter van der Krogt:
The 'Plenilunium' by Michael Florent van Langren. The first lunar map with names
Cartographica Helvetica 11 (1995) 44–49
The desire to name the topographic features on the surface of the moon arose with the invention of the telescope in the 17th century. The oldest known selenonymic notes and a map were produced by William Gilbert, although with no technical means of assistance. Because it took many years until Gilbert's results were finally printed, the Plenilunium, published in 1645 by Michael Florent van Langren, is considered to be the first printed moon map. Lunar maps, drawn by Johannes Hevelius from Danzig (1647) and Giovanni Battista Rievioli from Ferrara (1651), followed in short intervals.
The Southern-Dutch cosmographer Van Langren (1598–1675) was in service in Brussels to King Philipp IV of Spain, who supported his scientific studies. He developed a useful method for determining accurate geographic longitudes (important especially for navigation) by observing the time difference between the lightening and darkening of the lunar mountains during the waxing and waning of the moon. For this purpose an accurate map with names for the easy recognition of the different mountains and other lunar features was a real necessity.
Van Langren sketched a first selenography in 1627. A lack of funds prevented the publication of his ideas for years. The Plenilunii Lumina Austriaca Philippica, showing 322 names, was finally engraved in copper and printed in 1645. Contrary to Gilbert, both Plutarch and later Van Langren named the dark spots 'Mare' or 'Oceanus'. From the initial intention of using the names of famous scientists, popular rulers and monarchs for his nomenclature, only three names have been preserved in today's lunar maps: the craters Langrenus (named after himself), Pythagoras, and Endymion.