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.

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.