As described in 400 Years of the Telescope, Galileo's turning the telescope to the heavens in 1609 was a watershed moment in the history of astronomy. With his "spyglass," Galileo was able to see things no one else had seen before and to change the way human beings understood their place in the universe.

We encourage all teachers and students to take a look through a telescope and have the same "wow" experience that Galileo had. But even without a telescope, you can give your students a taste of what Galileo did and realized. We encourage you to have the students watch the film first. After that, you can do the following classroom activities, which illustrate two of Galileo's major discoveries:

• Jupiter's Moons

  Galileo's observations of Jupiter through his telescope showed that the giant planet had four moons orbiting around it. One of the key philosophical underpinnings of our western view of the universe at the time was that everything had to orbit the Earth. Galileo's observations of Jupiter's moons showed that they had not "gotten the memo" and had the audacity to orbit Jupiter.

  In Observing the Moons of Jupiter, students are provided with images from nine nights of observing Jupiter's moons and encouraged to measure the "month" for each moon. In this activity, students are put in the role of scientists, asking questions, evaluating observations, discussing their results with each other. (We are very grateful to Wil van der Veen and his coauthors, and the GEMS Program at the Lawrence Hall of Science, for permission to share this activity.)

• The Changing Appearance of Venus

  In the previous century, Copernicus had already suggested that the Sun, and not the Earth, might be the center of motion. However, it was possible to see his suggestion merely as a mathematical tool that made figuring out celestial motions easier. Galileo was able to make a simple, direct observation which showed that the planet Venus must orbit around the Sun and not the Earth.

  In Galileo Was Right!, students use simple materials and their own bodies and movement to simulate an Earth-centered and Sun-centered system. They observe the appearance of Venus as it orbits (just as Galileo did) and draw their own conclusion about which system is right.

  Virtual Venus is a more sophisticated version of this activity, in which students gather their own telescopic views of Venus, using a robotic telescope (or their own), and are led to an even deeper understanding of how Galileo showed that the Sun must be at the center of things.