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Timeline

Copernicus

1473-1543

Tycho

1546-1601Kepler

1571-1630

Galileo

1564-1642

Newton

1642-1727

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Geocentric (Ptolemaic)

System• The accepted model for

1400 years• The earth is at the center• The Sun, stars, and

planets revolve around the earth: explains daily movement

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Heliocentric (Copernican) System

• Sun at center (heliocentric)• Uniform, circular motion• Moon orbited the earth, the earth orbited

the sun as another planet

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Galileo

• Turned a telescope toward the heavens• Made observations that:

– contradicted the perfection of the heavens• Mountains, valleys, and craters on the Moon• Imperfections on the Sun (sunspots)

– Supported the heliocentric universe

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The skies change

• Tycho observed 2 phenomena that showed the heavens DO change:– Noticed a new star in the constellation

Cassiopeia– Noticed a Comet in the year 1577

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Johannes Kepler• Kepler succeeded Tycho (Tycho’s assistant) • He discovered that the earth and other

planets orbit around the sun. • Suspecting the sun had a force over the

planets, he investigated magnetism• It did lead him to the idea of elliptical

orbits.

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A force for planetary motion

• Newton proposes a force which controls the motion of the planets – GRAVITY

• The larger the mass, the larger the force of gravity

• The further the distance, the smaller the force of gravity

• Newton’s law of gravity F =mg

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Gravity