His discovery of the "Medicean Stars" was acknowledged by his nomination (July 1610) as philosopher and mathematician extraordinary to the grand-duke of Tuscany.
Giovan Gastone was the last Medicean grand duke; being childless, it was agreed by the treaty of Vienna that at his death Tuscany should be given to Francis, duke of Lorraine, husband of the archduchess Maria Theresa, afterwards empress.
Years had healed the breach between him and the Medicean family; and on the occasion of the Pazzi conspiracy against the life of Lorenzo de' Medici, he had sent violent letters of abuse to his papal patron Sixtus, denouncing his participation in a plot so dangerous to the security of Italy.
Probably also his exclusive belief in experimental methods, and slight regard for mere authority whether in science or art made the intellectual atmosphere of the Medicean circle, with its passionate mixed cult of the classic past and of a Christianity mystically blended and reconciled with Platonism, uncongenial to him.
Henry II.'s queen was Catherine of the Medicean family; and her children, Charles IX.