The 100 billion suns are the stars in our own galaxy, the Milky Way--as interpreted, with intelligence and good humor, by the director of the Max Planck Institute for Astrophysics, in Munich. Kippenhahn's concerns are with stellar evolution, stellar energies, and the dynamics of nuclear fusion and energy transmission. Much of this is familiar ground, but Kippenhahn adds a fresh emphasis on how computers can now generate stellar models in the proverbial twinkling, spewing out temperature, pressures, and other data about what goes on at the center of stars. He moves quite rapidly from pioneering investigations of stellar dimensions, and before long the reader is launched into analyses of the Hertzsprung-Russell diagram, that Baedeker that tells you where stars are positioned in the grand scheme of things: whether, like our sun, they are middling-sized and committed to a long stay on the main sequence, or whether they have already moved out to become red giants or white dwarfs. The discourse allows Kippenhahn to reminisce about colleagues in Germany and the US (where he has taught), and to produce apposite quotes from luminaries like Kant (who surmised the existence of galaxies) and Eddington (who saw nuclear energy as the only possible fuel for stars). Chapters deal with the birth, maturity, and end of stars, ranging from our own to distant galaxies and the universe itself. All this is neatly done, making the volume good of its type. What remains particularly memorable, however, is a lovely extended simile early on. The astronomer, Kippenhahn tells us, is like a fruitfly who yearns to observe the aging process in humans. Alas, the fruitfly lives only a day. So it is with astronomers, who receive ""a momentary impression of the totality of all the stars."" Effective, and also touched with the ineffable.