Observing the Solar System

Greek Observations Greek astronomers believed Earth to be the center of the universe. This is known as a geocentric system.

The Copernican Revolution Copernicus thought that the sun is at the center of the system of planets. This system is called a heliocentric system.

Galileo's Evidence Galileo Galilei used the newly invented telescope to make discoveries that supported the heliocentric model. Galileo saw 4 moons revolving around Jupiter, proving not everything revolves around Earth. Galileo saw Venus go through a series of phases, which wouldn’t happen if it only circled around Earth.

Kepler’s Calculations Kepler, who was once the assistant to a successful astronomer that died before their research was complete, had concluded from his calculations that the orbit of each planet is an ellipse instead of a perfect circle.

Modern Discoveries Since Galileo’s time, we have discovered Uranus, Neptune, and Pluto (which is no longer a planet). Today we know that the solar system consists of the sun, the planets and their moons, and several kinds of smaller objects that revolves around the sun.