Galileo 's Sidereus Nuncius ( Starry Messenger ) , which announced celestial observations through his telescope , does not mention Copernican heliocentrism , a theory that placed the Sun at the center of the universe . Galileo 's Sidereus Nuncius ( Starry Messenger ) , which announced celestial observations through his telescope , does not explicitly mention Copernican heliocentrism , a theory that placed the Sun at the center of the universe .