Chapter 1: The Flower and the Bee -- Chapter 2: Astronomy from the Top Down: Percival Lowell -- Chapter 3: Astronomy from the Bottom Up: Edward Emerson Barnard -- Chapter 4: Rivals of Mars -- Chapter 5: A Tale of Two Telescopes -- Chapter 6: The Spokes of Venus -- Chapter 7: Adventures with the Bruce -- Chapter 8: Percival Returns -- Chapter 9: Canali! Canali! -- Chapter 10: Wisps, Tores, and Good and Bad Reviews -- Chapter 11: A Barnard Ally Ups the Ante -- Chapter 12: Vale Percival -- Chapter 13: Ad Astra Edward -- Chapter 14: Lowell and Barnard Compared.

Using the "Parallel Lives" approach adopted by the Greek biographer Plutarch, noted historian of astronomy William Sheehan contrasts the lives and research careers of two famous astronomers, Percival Lowell and Edward Emerson Barnard. Drawing on vast archival materials and hitherto unpublished source materials, Sheehan documents in detail the contributions of these two late 19th and early 20th astronomers. Living at a time when controversies about Mars peaked, when great observatories were being built, and when research increasingly turned away from the Solar System toward the stellar and extra-galactic universe, these observers made spectacular contributions to astronomy. Their work still inspires, and continues in Perseverance rover's explorations of the surface of Mars carrying forward Lowell's dream of showing that Mars may once have been "the abode of life," and in Barnard's pioneering wide-angle photographs of the Milky Way which first showed the sweep, majesty and complexity of the Galaxy. The work of decades of research and writing, Sheehan has produced what is likely to become the definitive work on these two great astronomers. William Sheehan's many books include the authoritative biography The Immortal Fire Within: The Life and Work of Edward Emerson Barnard and (with Jim Bell) Discovering Mars: A History of Observation and Exploration of the Red Planet, which has been called the "gold standard of books on Mars" (Michio Kaku). .