Kenneth Lang's classic work Astrophysical Formulae. (Vol. I and II) is now available as soft cover edition in a set. This volume is a reference source of fundamental formulae in physics and astrophysics. In contrast to most of the usual compendia it carefully explains the physical assumptions entering the formulae. All the important results of physical theories are covered: electrodynamics, hydrodynamics, general relativity, atomic and nuclear...