This is the scarce first edition of writings by a leading learned society in Bologna, the Accademia dei Gelati. The volume includes striking woodcuts by the astronomer Geminiano Montanari of white stars against a black background. Montanari compares his observations of the Pleiades and Orion with those of Galileo from the Starry Messenger (1610). This article also reports, for the first time in book form, Montanari’s work on the bright variable star Algol (”the demon star”) in the constellation Perseus. Algol is understood today as an eclipsing binary star, where two stars revolve around a common center of gravity and appear to Earth to dim as they alternately eclipse one another. In antiquity the star was linked to the Gorgon’s head, the eye of Medusa, whose gaze would turn the viewer into stone. Scientifically, in Galileo’s world, a variable star would seem to contradict the Aristotelian maxim of the immutability of the heavens.