"Like fish in the sea" Jerónimo Muñoz and the elimination of celestial spheres. Edition and translation of the manuscript Questio de orbibus

Jerónimo Muñoz, the most important Spanish astronomer in the second half of the 16th century, left numerous manuscript treatises. They include a brief questio entitled «Utrum sint plures orbes coelestes necne» written in the late 1560s. In this article, we offer the first transcription of this opuscule, accompanied by an English translation. The presentation and translation notes point to the importance of this text in contemporary cosmological debates by rejecting the existence of the orbs or solid celestial spheres and postulating a sky of air, through which planets and comets move "like fish through water".