Models of the Solar System
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Models of the Solar System
Florida Benchmark
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SC.8.E.5.8 Compare various historical models of the Solar System, including geocentric and heliocentric.
Models of The Solar System
What is a planetary system?
• A planetary system is a star and all of the celestial bodies that revolve around it.
• An example of a planetary system is the solar system which includes the sun and the planets and other celestial bodies orbiting the sun.
Models of the Solar System
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What is the Center of the Solar System?
• The early scientists, in their attempt to answer this fundamental question created various models of the solar system.
• Models, which placed Earth at the center, are called Earth-centered, or geocentric, models.
Models of the Solar System
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The Geocentric Model
• The early philosopher and astronomer believed that everything in the universe is “perfect”; and that the planets are perfect spheres circling in perfect circular orbits.
• They believed the Earth was the most important object in space and therefore assumed it to be the center of the universe.
Models of the Solar System
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http://commons.wikimedia.org/wiki/File:Ptolemaic_system_2_(PSF).png
The Geocentric Model
• Aristotle, a Greek philosopher reasoned that if Earth circled around the sun, then the relative positions of the stars would change as Earth moves.
• This apparent change in the position of an object when viewed from different angles or locations on Earth is known as parallax.
• What Aristotle did not take into account is the fact that stars are very far away. At such great distance parallax cannot be observed without a telescope.
Models of the Solar System
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The Geocentric Model
• The geocentric model of the solar system became a very important part of ancient Greek Astronomy beginning in the sixth century B.C.E.
• The Greek philosopher Aristotle (384–322 B.C.E.) was among the first scholars to put forward an Earth-centered model of the Solar System.
• His model positioned the moon, sun, planets, and stars on a series of circles that moved around Earth.
Models of the Solar System
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The Geocentric Model
• Aristarchus, a Greek astronomer and mathematician, is believed to have proposed a sun-centered model of the solar system.
• Ptolemy an astronomer, geographer, and mathematician, exploited Aristotle’s Earth-centered view and developed a complex geocentric model that was used by astronomers over the next thousand years.
Models of the Solar System
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The Geocentric Model
• According to Ptolemy’s model, the planets moved on small circles that in turn moved on larger circles.
Historical Models of the Solar System
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http://commons.wikimedia.org/wiki/File:Geocentric_system.png
The Geocentric Model
• Ptolemy’s “wheels-on-wheels” model seemed to make sense since it very well illustrated observations made at the time going back hundreds of years.
• Scientist for many centuries used Ptolemy’s model to make predictions of the motions of planets years into the future.
Historical Models of the Solar System
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The Heliocentric Model (Sun-Centered)
Historical Models of the Solar System
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The Heliocentric Model
• The model which placed the sun at the center is called the heliocentric or sun-centered model.
• The Polish astronomer Nicolaus Copernicus watered-down Ptolemy’s model of the solar system since he thought the model was way too complicated.
• Although Copernicus adopted Ptolemy’s idea that planets’ orbits are perfect circles, he however developed Aristarchus’s primitive sun-centered model into a well thought out heliocentric model.
Models of the Solar System
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The Heliocentric Model
• The heliocentric model was fiercely rejected until it was refined and published by Copernicus and J. Kepler, a German mathematician, in the late 16th to early 17th centuries.
• Copernicus’s model eventually became more widely accepted as it fit observations significantly better than Ptolemy’s geocentric model.
• Copernicus’s model is known as the most influential of modern astronomy.
Models of the Solar System
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The Heliocentric Model
• Galileo Galilei was a scientist who conducted his experiments in the manner of moderns scientists. He actually used a very systematic approach very similar to the scientific methods.
• Galileo’s observations showed that they are other celestial objects beside Earth with orbiting satellites.
Models of the Solar System
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The Heliocentric Model
• His discovery best fit the heliocentric model.
• Galileo also observed that Venus went through phases similar to the phases of Earth’s moon.
• The observation of these phases was more in line with the idea that planets revolve around the sun rather than the Earth.
Models of the Solar System
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