A third of humanity no longer sees the stars. By 2050, one in two people could be deprived of them. This is one of the consequences of light pollution. It also impacts all living things, animals, plants, but also us, humans, by influencing the quality of our sleep in particular. The overproduction of energy fueling this nocturnal pollution calls into question our lifestyles. What is the need to consume so much? What solutions are there to free ourselves from them? Continually invading the night sky in the four corners of the globe, light halos are also a real threat to astronomy: the preserved areas essential for scientists' observations are becoming increasingly rare. But it is also our intimate relationship with the sky and our environment that is being questioned... Because we need the stars, and men and women are mobilizing to save them.