ASTRONOMERS IN HISTORY

ARISTOTLE

• 384 BC - 322 BC
• He proved the earth is a sphere because of the shadows on the moon.
• He beleived that the universe was finite because it has a center.

PTOLEMY

• Believed to have lived 90-168 AD
• He believed that the earth wad the center of the universe
• and made astronomers beleive that it slowed and stopped
• rotating.
• He did not contribute much, because his belief was wrong.

ARISTARCHUS

• 310 BC - 230 BC
• He believed that the sun was the center of the solar system.
• He was the first person to make a model of the solar system
• that showed the sun as the center, not the earth.

COPERNICUS

• 1475-1543
• He believed that the sun was the center of the universe.
• He proved mathimatically that his beliefe about the
• sun was correct by showing how the planets moved
• around the sun.

KEPLER

• 1571-1630
• He believed that the planets all moved slowly around the sun.
• He discovered three laws of planetary motion.

Kepler's First Law

The orbit of each planet is an ellipse with the sun at one focus of the ellipse.

Kepler's Second Law

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

Kepler's Third Law

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

GALILEO

• 1564-1642
• He believed strongly that earth and all other planets
• revolved around the sun.
• He discovered four of jupiters moons.