Venus moon: an astronomical tale of illusions and deceptions

What do a Neapolitan lawyer, a famous Italian astronomer, a Scottish instrument maker, the greatest French writer of adventure novels and a curious Belgian journalist have in common? Perhaps, it may be surprising to discover that they all are main characters of a story concerning the mysterious satellite of Venus. And if the attentive reader must have immediately (and correctly) thought “But Venus has no satellite!”, it will be even more astonishing to realize that, for more than two centuries, some of the most eminent scholars really believed in the existence of such a celestial body. In fact, starting from the seventeenth century, recurrent sightings of a hypothetical satellite occurred, leading several astronomers to go looking for it. Among them, the Italian Giovanni Domenico Cassini (1625-1712), who claimed to have seen something resembling a moon once in 1672, and again in 1686. 2022 is the 350th anniversary of his first alleged sighting; this work is thus aimed to trace the most relevant and curious passages of such a long and fascinating astronomical research.