Download 27.2 Models of the Solar System (p 691

27.2 Models of the Solar System (p 691-94)
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Name_________________________ Per._______
The first astronomers to study the sky thought the Sun, the planets, and the stars revolved
around the _____________. This model of our solar system is called the Earth-centered or
_______________ model.
A Greek astronomer named ___________, was the first to challenge this model because he
observed the planets traveling ____________ in the night sky. He called these planet motions
______________.
It wasn’t until 1543 that an astronomer named ___________________ proposes a ______ ________ or Sun-centered model of the solar system. His explanation to why planets were
moving backwards was that each planet orbited the _________ at a different ________, causing
faster moving planets to ________ slower moving planets. This explained why planets
sometimes appeared to move __________ from our perspective from Earth.
Later in the 1600’s ___________ observed four ________ traveling around the planet ________.
This observation changed the way people thought about our solar system because this
observation showed that objects can _________ around objects other than ________.
Kepler discovered that planets did not make perfect circular orbits around the sun, but moved in
___________. The more_______________ a planets orbit is the more elongated the orbit
becomes.
Newton greatly increased our understanding of the planets motion around the Sun when he
discovered that ___________ keeps the planets in motion, while __________ keeps planets in
their circular motion around the Sun.
The farther from the Sun that a planet is the ____________ the gravitational pull. This explains
why the outter planets orbit ________ than the inner planets, and why their orbits have gentler
_________ than the inner planets.