For nearly all of human history, the night sky was a realm of serene permanence, a source of myth and wonder. But that ancient peace is an illusion. We live in a cosmic shooting gallery, surrounded by millions of rocky and icy remnants from the formation of our solar system. This book reveals the story of how we shattered that illusion, tracing our journey from viewing comets as divine omens to understanding the cataclysmic impact that wiped out the dinosaurs. It explores the history of celestial encounters, from the Tunguska event that flattened a remote Siberian forest to the Chelyabinsk meteor that exploded over a modern Russian city, demonstrating that the threat from the heavens is not just ancient history, but a clear and present danger. Delve into the science behind the peril. Discover the true nature of asteroids and comets—what they are, where they come from, and the complex gravitational dance that can send them on a collision course with Earth. Journey to the vast reservoirs of the Asteroid Belt, the frozen Kuiper Belt, and the mysterious Oort Cloud. This comprehensive guide breaks down the terrifying physics of a celestial collision, detailing the spectrum of effects from a localized airburst capable of leveling a city to a planet-altering impact that can trigger a global winter and rewrite the future of life on our world. But this is not simply a story of doom; it is a story of hope and unprecedented human ingenuity. For the first time in our planet’s 4.5-billion-year history, a species has emerged that can not only understand this cosmic threat but do something about it. Learn about the emerging science of planetary defense and the global network of “sky sentinels” who tirelessly search for hazardous objects. Explore the remarkable technologies being developed to protect our world, from the triumphant success of NASA's DART mission, which proved we can deflect an asteroid, to advanced concepts like gravity tractors and lasers. This is the chronicle of our transition from passive targets to active guardians of our own planet, a testament to our fragile existence in a perilous cosmos and our remarkable ability to rise to the challenge.