1. Historic Models of the Solar System
Essential Question: How have theories changed the models of our Solar System?
Objective:
1. Compare and contrast heliocentric and geocentric models of the Solar System.

2. What is the difference between heliocentric and geocentric?
Unit 3 Lesson 1 Historical Models of the Solar System
What is the difference between heliocentric and geocentric?
Helio means sun and centric means center.
In the heliocentric model, Earth and the other planets orbit the sun.
Geo means earth and centric means center.
In the geocentric model, the Earth is the center with the sun, moon, and planets circling it.
A Theory is a set of ideas based on many observations. Theories usually change over time when new evidence is presented.
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3. Aristotle
Geocentric model
His model placed the moon, sun, planets, and stars on a series of circles that surrounded Earth.
Aristotle thought that if Earth went around the sun, then the relative positions of the stars would change as Earth moves.

4. Aristarchus
Heliocentric model
His model placed the earth and other planets on a series of circles that surrounded Sun.
Attempted to measure the relative distances to the moon and the sun became a major contribution to science.

5. Ptolemy
Geocentric model
In Ptolemy’s model, the planets moved on small circles that in turn moved on larger circles (wheels on wheel system)
Ptolemy’s model allowed prediction of the motions of planets years into the future.

6. Copernicus
Heliocentric model
Copernicus adopted Ptolemy’s idea that planetary paths should be perfect circles.
Wheels on wheels model
Copernicus’s model is generally seen as the first step in the development of modern models of the solar system.

7. Kepler
Heliocentric model
After careful observation and analysis, he realized that planetary orbits were not circular but were more like ellipses.
He formulated three principles, which are today known as Kepler’s laws.

8. Showed that Earth was not the only object that could be orbited.
Galileo
Heliocentric model
He improved the newly invented telescope and used it to view celestial objects.
He observed the moons Io, Europa, Callisto, and Ganymede orbiting Jupiter.
Showed that Earth was not the only object that could be orbited.
Observed that Venus went through phases similar to the phases of Earth’s moon.