WH 2: "Changing Views of the Universe" (After the Scientific Revolution)

Changing Views of the Universe

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Until the mid-1500s, Europeans’ view of the universe was shaped by the theories of the ancient writers Ptolemy and Aristotle. More than 1,000 years before the Renaissance, they had taught that Earth was the center of the universe. Not only did this view seem to agree with common sense, it was accepted by the Church. In the 1500s and 1600s, however, people began to question this view.
Copernicus Challenges Ancient Astronomy

In 1543, Polish scholar Nicolaus Copernicus (koh pur nih kus) published On the Revolutions of the Heavenly Spheres. In it, he proposed a heliocentric, or sun-centered, model of the universe. The sun, he said, stands at the center of the universe. Earth is just one of several planets that revolve around the sun.

Most experts rejected this revolutionary theory. In Europe at the time, all scientific knowledge and many religious teachings were based on the arguments developed by classical thinkers. If Ptolemy’s reasoning about the planets was wrong, people believed, then the whole system of human knowledge might be called into question. But in the late 1500s, the Danish astronomer Tycho Brahe (tee koh brah uh) provided evidence that supported Copernicus’s theory. Brahe set up an astronomical observatory. Every night for years, he carefully observed the sky, accumulating data about the movement of the heavenly bodies.

After Brahe’s death, his assistant, the brilliant German astronomer and mathematician Johannes Kepler, used Brahe’s data to calculate the orbits of the planets revolving around the sun. His calculations supported Copernicus’s heliocentric view. At the same time, however, they showed that each planet does not move in a perfect circle, as both Ptolemy and Copernicus believed, but in an oval-shaped orbit called an ellipse.

Galileo’s “Heresies”

Scientists from many different lands built on the foundations laid by Copernicus and Kepler. In Italy, Galileo Galilei assembled an astronomical telescope. As you have read, he observed that the four moons of Jupiter move slowly around that planet—exactly, he realized, the way Copernicus said that Earth moves around the sun.

Views of the Moon

Galileo sketched the views of the moon he saw through his telescope in 1609. Pictures of the moon taken through a modern telescope look remarkably similar.

Galileo’s discoveries caused an uproar. Other scholars attacked him because his observations contradicted ancient views about the world. The Church condemned him because his ideas challenged the Christian teaching that the heavens were fixed in position to Earth, and perfect.

Vocabulary Builder

In 1633, Galileo was tried before the Inquisition, and for a year afterward he was kept under house arrest. Threatened with death unless he withdrew his “heresies,” Galileo agreed to state publicly in court that Earth stands motionless at the center of the universe. Legend has it that as he left the court he muttered, “And yet it moves.”

We will move back to today's lesson plan: WH 16 September 2009.