Chapter 20 Section 1 Key Concepts: What are the geocentric and heliocentric systems? How did Copernicus, Galileo, and Kepler contribute to our knowledge of the solar system? What objects make up the solar system? Key terms: geocentric, heliocentric, ellipse

Earth at the center Greek observations: Several points of light seemed to wander slowly among the stars. Greeks named these objects planets, meaning “wanderers”. They believed the earth was at the center, and that it was inside a rotating dome they called the celestial sphere. Their model is “geocentric”, meaning earth centered.

Ptolemy About AD 140, Greek astronomer Still though Earth was in a geocentric solar system But he explained the movement of the other planets better

Sun at the center Heliocentric (sun centered) Earth and other planets move around the sun

Copernicus 1543, Polish astronomer Copernicus was able to work out the arrangement of the known planets and how they move around the sun.

Galileo Galileo used the newly invented telescope to make discoveries that supported the heliocentric model in the early 1600s. Specifically, his observations of Venus supported the heliocentric model

Tycho Brahe In the 1500s, Danish astronomer Brahe made very accurate observations for more than 20 years. He recorded the movement of the planets. He died in 1601

Kepler Brahe’s assistant. Tried to figure out Mars’ orbit, and found out that it was an ellipse (oval shape). He applied this to the other planets as well.

Modern discoveries Today we know that the solar system consists of the sun, the planets and their moons, and several kinds of other small objects that revolve around the sun.