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.