ASTRONOMERS IN HISTORY

ARISTOTLE

• Aristotle was a Greek philosopher.
• He lived from 384-322 BC and spent his life in Greece.
• He thought that the Earth was the center of all things and that if Earth went around the sun, then the relative positions of the stars would change as Earth moves.
• The model that he created placed the moon, sun, planets, and stars on a series of circles that surround Earth.

ARISTARCHUS

• Aristarchus was a Greek astronomer and mathematician.
• He lived from 310-230 BC and he lived in Samos, Greece.
• He attempted to measure the relative distances to the moon and sun.

PTOLEMY

• Ptolemy was an astronomer, geographer, and mathematician from Egypt.
• He was born in AD 90 in Egypt, (Roman Empire), and he died in AD 168.
• He belived that a celestial body traveled at a constant speed in a perfect circle.
• He developed a detailed geocentric model that was used by astronomers for the next 14 years. In his model, the planets moved on small circles that in turn moved on larger circles.

COPERNICUS

• Nicolaus Copernicus was a Polish astronomer.
• He was born on February 19, 1473, and he died on May 24, 1543. He was from Poland.
• He felt that Ptolemy's model of the solar system was too complicated.
• Nicolaus created a model that fit observations a little better than the geocentric model of Ptolemy.

KEPLER

• Johannes Kepler was a German mathematician and astronomer.
• He lived from December 27, 1571 to November 15, 1630 and was from Regensburg, Germany.
• After analyzing observations of the planets, he realized that requiring planetary motions to be exactly circular did not fit the observations perfectly.
• He formulated three principles, which today are known as Kepler's laws.

GALILEO GALILEI

• He was an Italian astronomer who approached questions in the fashion that today we call scientific methods.
• He lived from 384-322 BC and was from Italy.
• He used his powerful telescope to observe the moons Io, Europa, Callisto, and Ganymede orbiting Jupiter.
• His observations showed that Earth was not the only object that could be orbited.
• He made significant improvements to the telescope.

Geocentric model

The Geocentric Model is a model of the cosmos where Earth is at the orbital center of all celestial bodies.

Heliocentric model

The heliocentric model is a model that places the sun as the center of the universe, and the planets orbiting around it.

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