Models of the Solar System https://solarsystem.nasa.gov/multimedia/display.cfm?IM_ID=7783 Models of the Solar System (C) Copyright 2014 - all rights reserved www.cpalms.org 1

Models of the Solar System Florida Benchmark SC.8.E.5.8 Compare various historical models of the Solar System, including geocentric and heliocentric. (C) Copyright 2014 - all rights reserved www.cpalms.org 2

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. (C) Copyright 2014 - all rights reserved www.cpalms.org 3

Models of the Solar System 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. http://childrenlearningonline.net/children-science-Lessuniver1.html (C) Copyright 2014 - all rights reserved www.cpalms.org

Models of the Solar System 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 (C) Copyright 2014 - all rights reserved www.cpalms.org 5

Models of the Solar System 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. (C) Copyright 2014 - all rights reserved www.cpalms.org 6

Models of the Solar System 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. (C) Copyright 2014 - all rights reserved www.cpalms.org 7

Models of the Solar System 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. (C) Copyright 2014 - all rights reserved www.cpalms.org 8

Historical Models of the Solar System The Geocentric Model According to Ptolemy’s model, the planets moved on small circles that in turn moved on larger circles. http://commons.wikimedia.org/wiki/File:Geocentric_system.png (C) Copyright 2014 - all rights reserved www.cpalms.org 9

Historical Models of the Solar System 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. (C) Copyright 2014 - all rights reserved www.cpalms.org 10

Historical Models of the Solar System The Heliocentric Model (Sun-Centered) https://www.flickr.com/photos/nasablueshift/7368861386/ (C) Copyright 2014 - all rights reserved www.cpalms.org 11

Models of the Solar System 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. (C) Copyright 2014 - all rights reserved www.cpalms.org 12

Models of the Solar System 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. (C) Copyright 2014 - all rights reserved www.cpalms.org 13

Models of the Solar System 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. (C) Copyright 2014 - all rights reserved www.cpalms.org 14

Models of the Solar System 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. (C) Copyright 2014 - all rights reserved www.cpalms.org 15