This is a set offering the Springer books "Pioneer of Galactic Astronomy: A Biography of Jacobus C. Kapteyn" (ISBN 978-3-030-55422-4) and "Master of Galactic Astronomy: A Biography of Jan Hendrik Oort" (ISBN 978-3-030-55547-4). These accessible and entertaining biographies written by Piet van der Kruit chronicle lives and achievements of two pioneering astronomers of their time. KAPTEYN-BIOGRAPHY: This non-technical biography of Jacobus...