Transcript Lesson 1: Models of the Solar System

 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 time
 Stars seemed to move, but stayed in the same position relative to one
another
 Observed 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 orbit
 Elliptical (or oval shaped)
 (Italian) Galileo convinced others that
the heliocentric model was correct!
 (1610) Discovered 4 moons around
Jupiter

Not 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