This book marks the centenary of the remarkable invention of an opto-mechanical planetarium projector, the Zeiss Mk I. In May 1925, the first public planetarium opened at the Deutsches Museum in Munich. In the ensuing decades, this invention spread all over the world, becoming an integral part of modern life. The book presents a global narrative of the modern planetarium and its history through a selection of 100 objects and their stories. Written by a varied international group of contributors including planetarium professionals, scientists, historians, and other experts, these object stories highlight major developments in planetaria as they relate to advances in astronomy and space science as well as changes in society and culture at large. The objects featured in this book show how planetaria gained a central place in modern life at the intersection between science, education, art, and entertainment. They also connect the reader with the diverse people whohave made the modern planetarium a reality and continue to pave the way for its future - be they planetarium staff, scientists, architects, artists, engineers, educators, or planetarium visitors.