Galileo: Revealing the Universe

… for the Galaxy is nothing else but a mass of innumerable stars planted together in clusters.

—Galileo Galilei, Sidereus Nuncius (Starry Messenger), 1610

Ancient astronomers constructed explanations of the motions of the celestial bodies based on mathematics, philosophy, and careful observations of the skies as visible to the human eye. They recorded the positions of these heavenly bodies over time. Based on this method, ancient astronomers concluded that Earth was the center of the universe and that all other objects in the sky revolved around it.

In the 2nd century CE, a Roman astronomer named Ptolemy refined this view, stating that all planets moved in perfect circles, attached to perfect spheres, all of which rotated around the Earth: a theory that predicted the paths of the planets fairly well. This view, accepted for 1,400 years, was challenged by new astronomers, aided by instruments that enabled them to see the skies as they had never been seen before. Chief among them was Galileo, bolstering his observations with a revolutionary telescope he invented.

He carefully explored the night sky, turning his telescope to what looked like “dark” parts and discovering that they were filled with stars too dim to be seen without the telescope’s enhancement. In 1610, he published his observations of the solar system and distant stars in a volume called Sidereus Nuncius, or Starry Messenger.

In this lesson, students will practice close reading of passages from Galileo’s Starry Messenger concerning his observations of the stars and constellations through a telescope. They will develop an understanding of how he constructed his arguments to challenge the established views of his time using new technology and logical reasoning.

Guiding Questions

What did Galileo see when he looked at the sky through his telescope?

How did Galileo’s observations change our view of the universe and the Earth’s place in it?

Learning Objectives

At the end of this lesson students will be able to: Cite specific textual evidence to support analysis of a passage from Galileo’s Starry Messenger dealing with his observations of stars, constellations, and the Milky Way

Explain the significance of Galileo’s ideas to our understanding of the stars and the universe