49

Galileo’s telescope

revealed such things as

craters on the moon, and

he explained how that

evidence could be used to

test the prevailing Earth-

centered model of the

universe. He was

condemned by the

Inquisition in 1633.

(Science magazine [www.science

mag.org, 16 January 2009, page

326 [top].)

The Origin of Modern

4 Astronomy

Guidepost
The preceding chapters gave you a modern view of Earth. You can now imagine how
Earth, the moon, and the sun move through space and how that produces the sights
you see in the sky. But how did humanity fi rst realize that we live on a planet moving
through space? That required the revolutionary overthrow of an ancient and honored
theory of Earth’s place.
By the 16th century, many astronomers were uncomfortable with the ancient theory
that Earth sat at the center of a spherical universe. In this chapter, you will discover
how a Polish astronomer named Nicolaus Copernicus changed the old theory, how a
German astronomer named Johannes Kepler discovered the laws of planetary motion, and
how the Italian Galileo Galilei changed the way we know about nature. Here you will fi nd
answers to four essential questions:

How did classical philosophers describe Earth’s place in the universe?

How did Copernicus revise that ancient theory?

How did astronomers discover the laws of planetary motion?

Why was Galileo condemned by the Inquisition?

This chapter is not just about the history of astronomy. As they struggled to under-
stand Earth and the heavens, the astronomers of the Renaissance invented a new way of
understanding nature—a way of thinking that is now called science.