What Was the Geocentric Model? How Did the Heliocentric Model Develop?

Earth in the center of the universe

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Pattern of the stars didn’t change over timeStars seemed to move, but stayed in the

same position relative to one anotherObserved planets moving among the stars

Early observers thought Earth was at the center of the universe (Chinese) Thought Earth was under a dome

of stars (Greek) Thought the Earth was inside

rotating spheres nested inside each other Ge is Greek for “Earth” Geocentric model: Earth is at the

center of the revolving planets and stars

(140 A.D.) Ptolemy further developed the geocentric model (Greek)

Planets moved in small circles carried along in bigger circles

Explained motions in the sky fairly accurately

Accepted for nearly 1,500 years

Sun in the center

Aristarchus developed a sun-centered model (Greek)

Helio (Greek for “sun”)

The Earth and other planets go around the sun

Not well received in ancient times

(1543) Nicolaus Copernicus worked out the arrangement of the known planets and how they move around the sun

More evidence was needed to convince many people

(1500s) Tycho Brahe made more accurate observations

Johannes Kepler (Tycho’s assistant) Figured out the shape of the planet’s

orbitElliptical (or oval shaped)

(Italian) Galileo convinced others that the heliocentric model was correct!

(1610) Discovered 4 moons around JupiterNot everything in the sky

revolved around Earth Venus goes through

phases similar to the moon It would not have a full

set of phases if both it and the sun circled around Earth