Astronomy: science that studies the position, movements, structure and evolution of celestial bodies.

Astrology: study of the movements and relative positions of celestial bodies interpreted as having an influence on human affairs and the natural world.

One is a science, the other a type of divination, and yet astronomy and astrology both proceed from the same etymological - astron (ἄστρον), the star - and historical roots. When sky observation was done with a naked eye, when what exceeded human understanding was interpreted as a sign from the gods, the line between the two disciplines was very thin. They appeared to be fundamentally complementary and scientists often called themselves both astronomer and astrologer.

Through the collections of the Library of the Observatory of Paris, this exhibition offers to return to a time of a finite and regularly ordered universe, when stars' movements were of less interest for themselves than for what they could learn about Earth and Men.