Is Earth at the center of the universe?
The Greek philosopher Aristotle proposed that the heavens were composed of 55 concentric, crystalline spheres to which the celestial objects were attached and which rotated at different velocities, with the Earth at the center. People believed this for almost 2000 years, until Polish astronomer Nicolai Copernicus proposed that the Sun, not Earth, was the center of the solar system. His model, called a heliocentric system, said that Earth is just another planet (the third outward from the Sun), and the Moon is in orbit around Earth, not the Sun. While this might be true of our solar system, astronomers cannot see the whole universe through their telescopes, so no one knows where the true “center” of it lies.