ASTRONOMERS

ARISTOTLE

• 384-322 BCE
• He helped prove the earth was a sphere

ARISTARCHUS

• 310-230 BCE
• First person to make a model with the sun in the center

PTOLEMY

• 100-170 CE
• His tables were the most authoritative throughout the middle ages.
• He tried to explain the retrograde motion of planets

COPERNICUS

• 1473-1543
• Helped prove the sun was in the center and the planets orbit around it

KEPLER

• 1571-1630
• The orbits of planets are elliptical with the sun at one focus.
• Planets travel faster when close to the sun and slower when farther away.
• The period of time it takes a planet to orbit the sun is related to its distance from the sun.

GALILEO

• 1564-1642
• Proved the sun was the center of the universe
• Perfected the use of the telescope

NEWTON

• 25 December 1642 – 20 March 1727
• Discovered the law of gravity

HUBBLE

• November 20, 1889-September 28, 1953
• He devised some of the ways that galaxies are now classified.

GEOCENTRIC MODEL

• Model of the solar system with the earth in the center
• Aristotle and Ptolemy used this model

HELIOCENTRIC

• Model of the solar system with the sun in the middle
• Aristarchus and Copernicus used this model