Download What Did We Used to Think About the Solar System

What Did We Used to Think About the Solar
System?
Observing the Solar System: A History
The theory that the Earth is stationary was the basis of
ancient Greek theories that prevailed for over 2000 years.
The Movements of Planets and Stars
Geocentric Model (or Earth-centered): _______________
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As long ago as 6000 years,
astronomers recorded the
movements of stars and noted
that they appeared to move
across the sky, but did not
move in relation to each other.
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Ptolemy’s Geocentric Model
 Greek astronomer that lived in Egypt in the second
century A.D.
 was puzzled by retrograde motion (pattern of apparent
backward motion of planet movement)
 developed the first model that could be used to predict
locations of planets
 imagined planets on small circular orbits, called
_______________
 the center of each small orbit moved around Earth on a
larger circular orbit called a ________________________
 he believed that retrograde motion occurred when the
planet moved along the part of the epicycle that an
observer on Earth could see
 although his model did not work perfectly, it was the
accepted model until the 16th century
Copernicus’s Heliocentric Model
 Polish astronomer
 _________________________
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 suggested that Earth was a
planet, that it rotated, and that
Earth and the other planets
revolved around the sun
 was one of the first astronomers
to try to explain retrograde
motion
 Retrograde Motion → ___________________________
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Tycho, Kepler, and Planetary Motion
 Tycho Brahe was a 16th-centry Danish astronomer
 developed instruments to observe the moon, planets, and
other celestial objects
 ______________________________________________
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 identified a number of unexpected occurrences
(particularly in Mars’s orbit)
 his records were the most precise made before the
invention of the telescope
 Kepler (Tycho’s assistant) explained the unexpected
occurrences by suggesting that the planets’ orbits were
elliptical
 Kepler’s 1st law of planetary motion → ______________
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 Kepler’s 2nd law of planetary motion (equal area law) →
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 Kepler’s 3rd law of planetary motion (harmonic law) →
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Retrograde motion is observed because each planet orbits
the sun from a different distance and at a different speed.