The fourth edition of "Allen's Astrophysical Quantities" is a comprehensive reference book edited by Arthur N. Cox, featuring contributions from ninety authors. The book covers a wide range of astrophysical topics, including general constants and units, atoms and molecules, spectra, radiation, radio astronomy, infrared astronomy, ultraviolet astronomy, X-ray astronomy, γ-ray and neutrino astronomy, Earth, planets and satellites, solar system small bodies, the Sun, normal stars, stars with special characteristics, supernovae, star populations and the solar neighborhood, theoretical stellar evolution, circumstellar and interstellar material, star clusters, the Milky Way and galaxies, quasars and active galactic nuclei, clusters and groups of galaxies, and cosmology. The book also includes incidental tables and an index. It is designed to be a valuable resource for astronomers and astrophysicists, providing up-to-date and accurate data on various astrophysical quantities. The electronic version of the book is available for subscription and can be accessed on the publisher's website and CD-ROM.The fourth edition of "Allen's Astrophysical Quantities" is a comprehensive reference book edited by Arthur N. Cox, featuring contributions from ninety authors. The book covers a wide range of astrophysical topics, including general constants and units, atoms and molecules, spectra, radiation, radio astronomy, infrared astronomy, ultraviolet astronomy, X-ray astronomy, γ-ray and neutrino astronomy, Earth, planets and satellites, solar system small bodies, the Sun, normal stars, stars with special characteristics, supernovae, star populations and the solar neighborhood, theoretical stellar evolution, circumstellar and interstellar material, star clusters, the Milky Way and galaxies, quasars and active galactic nuclei, clusters and groups of galaxies, and cosmology. The book also includes incidental tables and an index. It is designed to be a valuable resource for astronomers and astrophysicists, providing up-to-date and accurate data on various astrophysical quantities. The electronic version of the book is available for subscription and can be accessed on the publisher's website and CD-ROM.