Models of the Solar System From Earth, it appears as though the stars, moon and sun are moving around us in the sky as we stay motionless. Ancient observers had no easy way to find out if this was correct or not. The idea that the Earth is at the center is called the geocentric model

Ptolemy’s Model The Greek astronomer Ptolemy added to the geocentric model around 140 A.D. His model explained the motions observed in the sky fairly accurately. Because of this, the geocentric model persisted for nearly 1,500 more years.

Heliocentric Model Copernicus (1550)- worked out the arrangement of the known planets and how they move around the sun

Kepler’s Model Kepler (late 1500s)- Discovered that the orbit of each planet was an ellipse: the orbits were an oval shape, not a perfect circle.

Galileo Galileo (early 1600s)- Collected evidence to gradually convince others that the heliocentric model was correct Used a telescope discovered 4 moons around Jupiter, proving that not everything revolved around the Earth Also discovered that Venus goes through phases similar to earth’s moons- this extra piece of evidence gave sided with the heliocentric model

Newton’s Law of Gravity Recall that Newton developed the 3 laws of motion. Using these laws he was able to prove that gravity and inertia working together explained the motions of the planets and their moons. This confirmed the heliocentric model was correct. Turn to page 170 in your packet. Read the page and complete Figure 2.