The Gauls were afraid the sky would fall on their heads. The Three Kings saw in the apparition of a new star, the beginning of a new era: The Christian Era. Sixteen centuries later, the great philosopher Pascal expresses his terror before the « eternal silence of the infinite spaces ». But since well before the dawn of humanity, the sky, the vault of the heavens, has continued to fascinate, intrigue and terrify. Len have sought to know more: astronomes have interrogated space with their eyes, their lenses and their telescopes. What do they do today? Now they listen to satellites, to electromagnetic signals from stars thousands of light years away. Has the element of poesie and fascination then disappeared? No. Like their Chaldean or Greek counterparts, astronomers are above all men of passion.