Genre: Nonfi ction/Expository
Comprehension Strategy: Monitor Comprehension Think-Aloud Copying Master number 8
Before Reading
Genre: Explain to students that you will read aloud a selection about Italian scientist Galileo and how he discovered the planet Jupiter’s four moons.
Remind students that they will learn about real people and real events because this is expository nonfi ction.
Expand Vocabulary: Introduce the following words to students before reading:
orbited: circled around
astronomer: someone who studies the stars and planets startling: surprising
evidence: proof
Set a Purpose for Reading: Have students listen to learn about the events that led to Galileo’s discovery.
During Reading
Use the comprehension Think Alouds during the fi rst reading of the story.
Notes about the genre and cultural perspectives may be used during subsequent readings.
41 Galileo and the Moons of Jupiter
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by Tony Helies
Four hundred years ago, most people believed that Earth was the center of the universe. Th ey thought that everything in the heavens, including the planets and the Sun, orbited our world.
An astronomer named Nicolaus Copernicus had written a book with a startling new theory: All planets, including Earth, orbit the Sun. Was Copernicus right or wrong?
In 1609, the Italian scientist and mathematician Galileo Galilei heard about a new device invented in Holland. Galileo thought it could help answer this question. Th e new instrument let the eye see distant objects as if they were nearby. It was the fi rst telescope.
Th e early telescopes were made with two pieces of curved glass, called lenses, set into a metal tube. Telescope lenses are like the lenses in eyeglasses. Both types of lenses work on the same principle: Curved glass bends light. Telescope lenses are designed so this bending magnifi es objects, making them look closer.1
Galileo was excited by the idea of using this new invention to look at the heavens. But these early telescopes were not powerful enough for astronomy. So Galileo set about building a better one. He worked for six months, experimenting with diff erent designs. His hard work paid off . Th e telescope he built made objects look thirty times closer than they did with the eye alone.
On January 7, 1610, Galileo pointed his telescope toward one of the brightest objects in the night sky, the planet Jupiter.
On either side of Jupiter, he saw little points of light arranged in a straight line, two to the left and one to the right.2
Galileo believed these were fi xed stars, and expected they would remain in place as Jupiter moved across the sky.
Th e next night, he was surprised to fi nd that the three stars were all to the right of Jupiter.
Galileo was puzzled. He had expected to fi nd the stars farther to the left of Jupiter. What had caused them to move to the right? He waited impatiently to see where these stars would be on the third night, but cloudy skies blocked his view.
Galileo and the Moons of Jupiter
1 This paragraph is mostly about early telescopes.
The author tells me how they were made and how they worked. This information helps me better understand what the author is writing about.
2 I wonder what these points of light are. I will read further to fi nd out.
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Th e next day, clear skies returned. Galileo was astonished by what he saw that night. Two of the stars had moved back to Jupiter’s left and one had disappeared.
Galileo suspected that the third object was behind Jupiter.
Over the next two nights, the three stars continued to move from one side of Jupiter to the other. Galileo now realized that the three points of light he was observing were orbiting Jupiter.
Th ey were moons, not stars.
Galileo had proved that not all heavenly bodies orbit Earth.
Th e Earth was not at the center of everything aft er all. Th is was the fi rst evidence supporting Copernicus’s theory. It helped create our modern view of the universe.³
On January 13, Galileo saw a fourth moon, which had been hidden behind Jupiter. Th ese four moons—Io (EYE-oh), Europa (your-OH-pah), Ganymede (GAN-ih-meed), and Callisto (kuh-LIH-stoh)—are today known as the Galilean moons, in his honor.
³ I think this paragraph is important because it explains what Galileo’s discovery meant, so I will reread it. In Galileo’s time, most people believed that all objects in space circled around Earth. Galileo proved that this was not true.
Genre Study Nonfi ction/
Expository: The writer shows the pronuncia-tion, or the way to say, the names of Jupiter’s moons. This informa-tion helps readers understand these un-usual words and adds to the reader’s knowl-edge of the topic.
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After Reading
Summarize: Work with students to summarize the events that took place over fi ve nights and led to Galileo’s amazing discovery. Help students by reading aloud passages.
Use Copying Master number 8 to prompt students to share a part of the selection they thought was diffi cult and how they were able to understand the text.
Cultural Perspective
Have students discuss what they have studied about astronomy or the solar system in science. The world’s
fi rst telescopes were used to spot advancing armies or ships, not to study outer space. Today, nations from around the world use telescopes to look deep into space. Scientists from the United States, the United Kingdom, Chile, Australia, Argentina, and Brazil share two of the world’s largest telescopes, the Gemini North, located in Hawaii, and its sister telescope, Gemini South, in Chile.
Think and Respond
1. The writer says Galileo spent six months building a telescope. Why does he say Galileo’s “hard work paid off ”? Possible responses: Galileo’s telescope was very powerful and helped him see stars far away; Galileo could see Jupiter with his new telescope and this led to his discovery about the orbits of the planets. Analytical
2. List two details that help us understand the sequence of events. Possible responses: In 1609; On January 7, 1610 Genre
3. This article describes one of Galileo’s important scientifi c discoveries. How does the writer help you understand the topic? Possible response: The writer describes the important events in sequential order. It is easier to understand what Galileo did each night and what he learned. Author’s Purpose