This book presents the story of an experiment with historical significance that, for the first time, uncovered the mechanisms responsible for solar energy production and those generating energy in massive stars. The results were obtained by directly measuring the neutrino fluxes produced by individual fusion reactions in the Sun and providing the initial evidence of nuclear reactions occurring in massive stars via the CNO cycle. The CNO cycle is theorized to be the primary channel for hydrogen burning in stars more massive than the Sun and is, in fact, the primary channel for hydrogen burning in the Universe. These groundbreaking discoveries stem from a singular 32-year experiment, spanning from 1990 to 2021.The book commences with the experiment's genesis, placing it within the historical context of astrophysics and astroparticle physics. It then delves into the detector's conceptualization, gently describing the techniques used and addressing the challenges in constructing the detector. The narrative is presented in a simple and popular style, maintaining rigorous scientific adherence to the obtained results.The book is intended for a general audience not necessarily familiar with science, especially physics, but with a curiosity and interest in astrophysics. It aims to reach those who may be unaware of the complexities involved in conducting a scientific experiment, particularly one pushing the limits of feasibility. Additionally, it may appeal to those interested in amateur physics or astrophysics. The core novelty of the book lies in its detailed exploration of an experiment, encompassing scientific, cultural, personal, and even sociological dimensions.
