1. TOPIC #1: Chapter 22 Origin of Modern Astronomy

2. Section 1: Early Astronomy Astronomy is the science that studies the universe. The “Golden Age” of early astronomy was centered in Greece. Ancient Greeks like Aristotle studied the motion of heavenly bodies by observing and recording the motions.

3. Section 1: Early Astronomy Early models of the solar system developed by the Greeks were geocentric models these models were Earth centered. This means that the sun, moon and other planets orbit the Earth. Orbit- The path of an object as it goes around anotehr object in space

4. Section 1: Early Astronomy

5. Some ancient Greeks believed in the heliocentric theory this was the idea that the Earth, moon and other planets orbit the sun. There was no way of measuring or collecting data that could support either theory during the times of the ancient Greeks?

6. Section 1: Early Astronomy Heliocentric Theory

7. Section 1: Early Astronomy Claudius Ptolmey (A.D. 141) defended the geocentric theory of the universe (which was later proven wrong). He believed that the motion of the planets across the nights sky was evidence of the geocentric theory. He even accounted for retrograde motion, which is the apparent westward motion of planets against the stars. The stars seem to move in an easterly direction but at times the planets seem to move in the opposite direction.

8. Section 1: Early Astronomy Retrograde motion did not help the geocentric theory but it defined the motion of planets “backwards”. It was later found that this was due to their own rotations on an axis.

9. Section 1: Early Astronomy Polish astronomer, Nicolaus Copernicus (1473-1543) is credited with discovering the heliocentric model of the solar system because he was able to support his discovery with data and evidence.

10. Section 1: Early Astronomy Danish astronomer, Tycho Brahe (1546-1601) advanced the study by inventing many tools used to observe and measure planetary motion. He had an assistant named Johannes Kepler (1571-1630) who furthered his study. Kepler is credited with discovering the Three Laws of Planetary Motion. These laws identify and define how planetary bodies orbit the sun and each other.

11. Section 1: Early Astronomy Kepler defined the shape of the path planetary bodies orbit in as an ellipse. From these laws of motion we have developed a way of measuring distance in space. The distance between the Earth and the sun is called an astronaumical unit (AU). This is used as the system of measurement when talking about any distance in space.

12. Section 1: Early Astronomy Galileo Galilei (1564-1642), an Italian astronomer was the first person to use the telescope to study space. He made many discoveries that supported Copernicus’s heliocentric model of the universe.

13. Section 1: Early Astronomy Sir Issac Newton (1642-1727) was a British astronomer who made arguably the most important discovery in all of astronomy. He is credited with defining and proving the existence of gravity. Gravity is the attractive force all objects have which determines the motion of objects in space.