1. Astronomy
An Ancient Science

2. Astronomy Is the oldest science
By careful observation the Babylonians, Egyptians, Aztecs, and Mayans could accurately predict the locations of the heavenly bodies.
They relied on stars for information such as when to plant their crops and when the seasons would change.

3. Early Observers Aristotle (384-322 B.C.)
Most influential thinker of his time
Suggested that everything in the universe is composed of 4 elements---earth, air, fire, & water.
Proposed that each element has a natural resting place with earth in the center surrounded by spheres of water, air, and fire.

4. Early Observers Aristotle (continued)
His model of the universe contained a total of eight spheres revolving around the Earth.
The first seven spheres carried the moon, the Sun, and the five known planets.
Beyond those seven spheres were tiny lamps fixed to another revolving sphere.

5. Early Observers Aristarchus (air us TAR kus) of Samos 3rd Century B.C.
Used math and observation to come up with his theories.
Suggested that the sun is the center of the universe– not the Earth
This rotation caused a cycle which we call a year
Suggested that day and night are caused by the rotation of the Earth on its axis.

6. Early Observers Aristarchus of Samos (con’t)
First to measure distance to the moon and sun by using math.
Thought the sun was further away than previously thought.
His theories were thought to be crazy and were not accepted by his people---not looked at for another 2000 years.

7. Early Observers Ptolemy (TAHL uh mee) 2nd century A.D.
Supported the ideas of Aristotle
Thought if the earth really moved, the high winds would blow birds off of trees.
Agreed with Aristotle that the sun revolves around a stationary Earth.

8. Ptolemy Found Two Major Problems with Aristotle’s Theory…
One
It could not explain why the planets varied in brightness from year to year– if they were the same distance away from the earth, they should not vary in brightness.

9. Ptolemy Found Two Major Problems with Aristotle’s Theory…
He felt that the paths that the planets traveled were more erratic than the paths suggested by Aristotle’s theory.
Ex: A planet such as Mars appears to make a loop in the sky going backwards for a while before continuing its forward motion. This is called retrograde motion

11. Solution to Problem Two
The solution to this problem was to add another motion to the planet.
Not only would it revolve in a circular orbit around a smaller earth but also it would make smaller revolutions about a point on its own orbit.