This is a thorough, very readable and excellently illustrated biography of Willem de Sitter (1872-1934), one of the most influential astronomers of his time, and also a co-author and correspondent of Einstein. Authored by a physicist and skilled writer, the book gives a beautiful and accessible description of the physics debated by Einstein and de Sitter, as well as the latter's alternative cosmological model, later known as the De Sitter Universe. But this is just part of a fascinating and varied life story involving numerous contributions to astronomy, as well as many places and personalities of early 20th century physics. The book will appeal to all those interested in astronomy and physics and their history.

Astronomy in Leiden.- Descent.- Youth and Education.- The Making of an Astronomer.- The Galilean Moons of Jupiter.-  The Road to Professor in Leiden.- Leiden Activities.- Fundamental Work and a new Theory for Jupiter's Satellites.- Gravity, General Theory of Relativity and Cosmology.-  Director of  the Observatory and Stay in Arosa.- At the Top.- International Business.- Last years.- Abbreviations.

Jan Guichelaar (1945) is a theoretical physicist. He studied mathematics, astronomy and theoretical physics at the University of Amsterdam and received his PhD in 1974 with a thesis on acoustics in relativistic kinetic Boltzmann theory. After a career in secondary education, politics, university education and educational management he has been active as a historian of science in the field of astronomy and physics.