The “Ashen Light” of Venus—a ghostly emission of light from the night side of our nearest planetary neighbor—is among the last unsolved mysteries of astronomical history. In the four centuries since the phenomenon was first reported, highly reputable visual observers of Venus have recorded seeing the Ashen Light, while others have spent a lifetime searching for it without once being convinced that they ever saw it. Is the Ashen Light a trick of the eye? The result of a defective lens? A real scientific event? Occasional references to the Ashen Light are scattered across the literature, yet no work to date has synthesized these records. This book therefore digs deep into the history of the mystery and our latest attempts to understand it, sifting through the clues that might explain whether it is caused by physics, is conjured up by the eye or brain, or a combination of both. This baffling story will appeal to amateur astronomers, hobbyists, and lay readers interested in joining the debate about one of the most elusive observable phenomena ever recorded in the night sky.