ARISTOTLE

• 384-322 BCE
• Gave the theory that the Earth was in the center of our solar system

ARISTARCHUS

• 310-230 BCE
• He attempted to measure the relative distance to the moon and sun
• He started a Heliocentric model but was rejected

PTOLEMY

• 100-170 CE
• He created a "wheels on wheels" system
• He wrote the book "Almagest"

NICOLAUS COPERNICUS

• 1473-1543
• Created a model that was accepted after his death.

JOHANNES KEPLER

• 1571-1630
• Figured out things don't revolve in a perfect circle.
• They revolve in ellipses.

KEPLER'S FIRST LAW

KEPLER'S SECOND LAW

A line segment joining a planet and the Sun sweeps out equal areas during equal intervals of time.

KEPLER'S THIRD LAW

The square of the orbital period of a planet is proportional to the cube of the semi-major axis of its orbit.

GALILEO GALILEI

• 1564-1642
• Improved the telescope
• Proved Earth isn't the only thing that can be orbited

ISAAC NEWTON

• 1643-1727
• Discovered gravity
• Created the universal law of gravitation

EDWARD HUBBLE

• 1889-1953
• Showed that the universe is expanding.
• Determined there were more galaxies beyond the Milky Way.