Models of the solar system The geocentric model; Heliocentric model

 Geocentric model; a model that puts Earth at the center of the revolving planets.  A Greek astronomer named Ptolemy thought the earth was the center of the universe. He came up with the theory of the geocentric model.  Ancient Greeks could see only five planets. They did not have telescopes. Other planets were far away and couldn’t be seen.  They believed that Earth stays in one place, and the other planets revolved around Earth, thus the geocentric model.

 Another astronomer named Kepler developed the heliocentric model by applying his knowledge of mathematics.  He discovered that the orbit of each planet is not a circle but an ellipse.  How did he reach his conclusion? Making measurements, interpreting data, making models, verifying hypothesis, communicating.  Kepler change Copernicus’s and Aristarchus’s earlier models that known planets move around the sun-known as the sun centered models or the early heliocentric models.

 Galileo further developed the heliocentric model. He used a telescope and discovered the four moons of Jupiter.  Why was this discovery important? He proved that they orbited Jupiter not earth, which proved that objects could orbit something other than earth.

 The work of Galileo and Kepler established the truth of the heliocentric model, but it did not explain why this model was correct. It took the work of Isaac Newton to explain the motion of objects in the solar system.  Inertia and gravity combine to keep objects in orbit.  What motion of Earth does this explain?Earth’s revolution around the sun.  What path of the moon does this explain? The moons orbit around Earth.

 Reminder: why does a baseball continue to move after a pitcher lets go of it and stops applying force? The ball has inertia, forward motion. Why would the ball eventually hit the ground? Gravity would pull it down. Newton realized that the moon is falling toward Earth just like an apple falls from the tree, but its inertia keeps it from falling to Earth. Another example of inertia is the classic magic trick in which a magician pulls a tablecloth off a table, leaving the dishes that were on top of it in place. What role does inertia play in this trick? The inertia of the dishes causes them to resist being moved.

 Students page 173 assess your understanding, 1a,1b,1c.  Classwork: draw a geocentric model.Illustrate details.  Draw a heliocentric model. Illustrate details. Include Galileo’s observation of Jupiter’s four moons.