Updated edition of a popular introduction to cosmology, now with new observational data, supporting web material, and problems with solutions An Introduction to Modern Cosmology is an accessible account of modern cosmological ideas that enables readers to understand cosmology without resorting to the mathematical apparatus of general relativity. This fully revised Fourth Edition of the bestseller takes an approach which is grounded in physics with a logical flow of chapters, leading the reader from basic ideas of the expansion described by the Friedman equations to some of the more advanced ideas about the early universe. The Advanced Topic sections present subjects with more detailed mathematical approaches to give greater depth to discussions. Student problems with hints for solving them and numerical answers are embedded in the chapters to facilitate the readers' understanding and learning. The new edition contains updated observational data, more detailed explanations and examples of the central-to-cosmology Friedman equations, and references to extensive online supporting material. It also incorporates up-to-date results from the Planck mission, which imaged the anisotropies of cosmic microwave background radiation over the whole sky. Sample topics explored in An Introduction to Modern Cosmology include: The geometry of the universe, covering flat, spherical, and hyperbolic geometry, infinite and observable universes, and the three values of kSimple cosmological models, covering Hubble's law, expansion and redshift, particle number densities, and evolution including curvatureThe density of the universe and dark matter, covering galaxy cluster composition and brightness of the supernovaeThe origin of light elements in the universe, covering hydrogen and helium, problems with the Hot Big Bang, and flatness and horizon problemsWritten in a clear, concise format with short, accessible chapters, An Introduction to Modern Cosmology is an essential textbook resource on the subject for advanced undergraduate and graduate students of astronomy, astrophysics, and physics.