This book was originally published in French and later translated to English.You don't have to have any prior scientific understanding to read this book as everything is explained and defined in the main narrative.
A planet orbiting a star other than our solar system's Sun is called an extrasolar planet or, more commonly, an exoplanet. You can imagine the immense difficulty in directly imaging these planets when you consider that the typical star would be about a billion times brighter than its orbiting exoplanet(s). Therefore, indirect methods to find exoplanets must be used. After an intriguing and brief introductory chapter, this is where this book begins.