1. Observing the Solar System
Chapter 14 Section 1
Observing the Solar System

2. Earth at the center: In a geocentric system, Earth is at the center of the revolving planets.
Sun at the center: In a heliocentric system, Earth and the other planets revolve around the sun.
Nicolas Copernicus worked out the arrangement of the known planets and how they move around the sun.

3. Galileo Galilei used the newly invented telescope to make discoveries that supported the heliocentric model.
Motion of the Planets:
1. Tycho Brahe Carefully observed and recorded the positions of the planets.
2. Johannes Kepler used Tycho Brahe’s data to develop three laws that describe the motions of the planets.

4. Kepler’s Three Laws
First Law: Kepler found that the orbit of each planet is an ellipse
Second Law: Kepler found that each planet moves faster when it is closer to the sun and slower when it is farther away from the sun.
Third Law: Kepler also found out that planets that are closer to the sun orbit the sun faster than planets that are farther from the sun.

5. Modern Views of the Solar System
Today we know that the solar system consists of the sun, the planets and their moons, and several kinds of small objects that revolve around the sun.
We use Astronomical units to measure distances in our solar system. One Astronomical unit is about 150 million Km. which is the average distance from the sun to the Earth