Ch. 15 Questions.

3,4,6,7,11,12.

3. Copernicus made a huge change to the Ptolemaic model of the solar system, so much that it was not called the Ptolemaic model afterward. He proposed the heliocentric model of the solar system, which has the sun at the center.

4. He observed stars and planets for twenty years before the invention of the telescope, and came up with the idea of stellar parallax, the idea that around the earth's orbit, nearer stars should appear to shift more than more distant stars.

6. Galileo studied the sun, and seeing the sun spots across the surface changing, decided that the sun was rotating. This fact supported Copernicus' idea that the Earth revolves around the sun.

7. Sir Isaac Newton proposed that an object in motion wants to stay in motion unless acted upon by an outside force, or inertia, and the law of universal gravitation. These affect how the planets move.

11. Planets are thought to be made up of gases, rocks, and ices. The terrestrial planets are made up of mostly rock and ice, and the jovian planets are made of gases. Jovian planets have lower densities, while terrestrial planets are higher densities.

12. There was the big bang, an unbelievably large explosion, which sent matter flying through the universe. When the matter, the gases, began to condense, they formed a nebular cloud. Then the nebular cloud was acted on by some outside force, and started to further condense. It became a flat disk shape with a large concentration at the center (which would become the sun). Matter starts forming clumps, called planetesimals. The planetesimals grew into protoplanets, which then became planets.