Definition: A gigantic cloud of dust and gas in the universe that clumps together to form stars and planets. Facts: The gas is mostly the smallest atoms- hydrogen and helium. The dust is extremely small particles too small to be seen with the eye. Gravity pulls the gas and dust together. Example: The eagle nebula. Non-example: The Milky Way galaxy which already has gone beyond a cloud of gas and dust to form a galaxy. Nebula

Definition: An explanation that is supported by a lot of evidence and which is widely accepted by scientists and other people. A theory can sum up a lot of observations and is used to make predictions. Generally a theory is a working hypothesis until new evidence comes along. It is not a fact! Ex: The theory of evolution keeps changing as we learn new facts. Examples: Theory of Evolution Theory of Plate Tectonics String Theory of Gravity Solar Nebula theory A good theory can be used to predict phenomena or behavior. The theory of evolution is a poor predictor. Theory

Definition: A pulling force that draws things with mass together. Facts: Gravity acts over extremely large distances. Gravity acts on the smallest of particles (a molecule or bit of dust or atom) to the largest of objects (a star, a galaxy and the universe). Example: Gravity pulls the Earth and Moon towards each other and keeps the moon in orbit around the Earth. Gravity pulls the Earth and Sun together and keeps the Earth in orbit around the Sun. Non-Example: Gravity is not friction or a pushing force. Gravity

First: The fusion rate increases. This means, hydrogen atoms fuse together to become helium until all of the hydrogen is used up. Some very low mass stars never go beyond this stage. They use up their hydrogen and cool and become like a planet. They are called Brown Dwarfs. Second: In big enough stars: the temperature increases and more energy is released. Some low mass stars use up all of their hydrogen, cool, and shrink. They become White Dwarfs. Third: Some moderate mass stars get brighter when they run out of hydrogen. The outer shell expands and cools. They become Red Giants. Their outer shell gets blown away and becomes a nebula while the core becomes a White Dwarf. Really massive stars end their lives by exploding as a Supernovae. The core will then collapse and become a black hole.

5 billion years ago: 75% hydrogen 25% helium Today: 35% hydrogen 65% helium 5 billion years in the future: 0% hydrogen 100% helium Earth’s temperature will be about 40 0 F hotter. The oceans will be gone. The Sun’s outer core will expand and the Sun will become a Red Giant. Theory #1: The Earth will get engulfed by the Sun and exist no more. Theory #2: When the Sun first begins to shrink, gravitational attraction between the Earth and Sun will become less. Some scientists think the Earth may move away from the Sun as gravity no longer holds them together. If this happens, the Earth will be a cold, desolate, barren rock in space.

Title Page: Solar Nebula Theory Page 1: Explain what a scientific theory is and is not. Use examples. Page 2: Describe a nebula. Page 3: Step 1: Draw a cloud of gas and dust (nebula). Describe how this cloud begins to contract due to gravity. Page 3: Draw a disk with a bulge at the middle. Describe how this forms from the nebula. Page 4: Draw a star with matter surrounding it. Describe how a star begins. Page 5: Draw a planetary system around the star. Describe how the matter forms into planets. Page 6: Describe the life cycle of an ordinary star.