Models of the Solar System (C) Copyright 2014 - all rights reserved

Models of the Solar System

(C) Copyright 2014 - all rights reserved www.cpalms.org

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Florida Benchmark


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.



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.



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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.



http://commons.wikimedia.org/wiki/File:Ptolemaic_system_2_(PSF).png


• 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.




• 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.




• 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.




• According to Ptolemy’s model, the planets moved on small circles that in turn moved on larger circles.

Historical Models of the Solar System


http://commons.wikimedia.org/wiki/File:Geocentric_system.png


• 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.



The Heliocentric Model (Sun-Centered)



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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.




• 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.




• 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.




• 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.



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Models of the Solar System (C) Copyright 2014 - all rights reserved