Astronomical History

Ptolemy expresses geocentric model 127AD Copernicus offers heliocentric model 1530

AD Tycho Brahe 1546-1601 takes precision

measurements Johannes Kepler analyzes Brahe’s data Galileo Galili proves heliocentric model Isaac Newton explains heliocentric model

Claudius Ptolemaeus An Alexandrian (from

Alexandria in Egypt) astronomer, about 150 AD

Like most of the Aristotlean world, they did not believe the natural world was orderly and rational and did not get involved in the practical world

Ptolomaen Astronomy

This view is called “geocentric” because the earth is placed at the center of the universe

To make the model work and explain retrograde motion, planets revolved in both cycles and epicycles around the earth

Retrograde Motion of Mars

Ptolemy’s Explanation of Retrograde Motion

Nicolaus Copernicus

Copernicus was a Polish canon of the Roman Catholic church.

He tried to find another astronomical system that was more philosophically and aesthetically pleasing than Ptolemy’s.

Copernican Model

The Copernican model held that planets revolved around the sun instead of the earth.

Copernicus did not provide much evidence in support of his model, he argued from philosophy.

Tycho Brahe

Tycho Brahe was court astronomer and astrologer to King Rudolph II of Bohemia. He used his position to build precision equipment to take precise astronomical measurements, for the first time in history.

Galileo Galilei

Galileo 1564-1642 In this picture, he is

developing the pendulum laws

Galileo observed mountains on the moon

Galileo observed moons orbiting Jupiter 1610

Galileo observed phases in Venus

Johannes Kepler

Johannes Kepler 1571-1630 Becomes Tycho Brahe’s

assistant 1600 Analyzes data and determines

the elliptical orbit of planets 1609

These laws removed all doubt that the Earth and planets go around the sun. Later Sir Isaac Newton used Kepler's laws to establish his law of universal gravitation.

KEPLER’S LAWS (1) The path of every planet in its motion

about the sun forms an ellipse, with the sun at one focus.

(2) The speed of a planet in its orbit varies so that a line joining it with the sun sweeps over equal areas in equal times.

(3) The squares of the planets' periods of revolution are proportional to the cubes of the planets' mean distances from the sun.

An Ellipse

Kepler’s Second Law

Isaac Newton

Isaac Newton 1642-1727

In 1664 explains Keplers’ Laws using the Universal Law of gravitation plus the mathematics of calculus