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Science test study guide for the last week in January 2011. 1. Our Sun is the center of our solar system. 2. Our Sun is a star around which planets, asteroids, meteoroids, and comets revolve. 3. Eight planets and the dwarf planet of Pluto revolve around the sun. 4. The inner planets are Mercury, Venus, Earth, and Mars. These planets have rocky surfaces and are called terrestrial planets. 5. The outer planets are Jupiter, Saturn, Uranus, and Neptune. The outer planets are called gas giants because they are made of gas and are much larger than the inner planets. 6. Day and night on planets vary from one planet to the next. Day and night are caused by the rotation on the axis of a planet. On Earth, it takes 24 hours for one rotation. 7. A year is calculated by how long it takes for a planet to revolve, or orbit, around the sun. It takes 365 Earth days for Earth to revolve around the sun. 8. Earth tilts on its axis at 23.5 degrees. Earth has seasons because of the tilt as it revolves around the sun. When the northern hemisphere is tilted away from the sun, it has winter. When the southern hemisphere is tilted towards the sun, it has summer. We live in the northern hemisphere. 9. The side of the moon facing Earth is always the same because the moon rotates once on its axis for each time it revolves around the Earth. We never see the far side of the moon. 10.The moon goes through phases. The phase we see of the moon depends on how much of the sunlit side of the moon is facing the Earth. 11. Eclipses occur when sunlight is blocked. An eclipse of the sun takes place when the moon is in the new moon phase and moves between the sun and the Earth. This is called a solar eclipse. An eclipse of the moon occurs when the moon is in the full moon stage and the Earth blocks sunlight from striking the moon. 12. Tides are the rise and fall of the ocean waters. Tides are not waves. The rise and fall is caused by the gravitational attraction of the moon on the oceans of the Earth. 13.The moon is about 1/4th the size of the Earth. 14.Galileo studied the moon through a telescope he had improved. He saw dark flat places on the moon and thought they were oceans. He called them maria because the word means seas in Greek and he spoke Greek. 15. Galileo also saw round pits on the moon and called them craters. 16. Scientists know a lot about the moon because astronauts went to the moon and collected rocks and brought them back to Earth to study. 17.Early man studying the moon had two theories about the universe. One theory was that the Earth was the center of our universe. That theory was called the geocentric theory. The other theory, which we today know is correct, is the theory that the sun is the center of the universe. That theory is called the heliocentric theory. 18. The sun produces energy by a process called nuclear fusion. Energy from the sun makes the Earth suitable for living things. 19. There are 3 layers of the Sun’s atmosphere. The layer we see in a photograph of the sun is the photosphere. The layers we can see during an eclipse are the chromosphere and the corona. 20. Sunspots are found on the surface of the sun. They are areas of gases that are cooler than the other gases on the surface. 21.Solar prominences link different sunspot regions to each other. 22. All the inner planets have rocky surfaces and are small compared to the gas giants. 23.Earth is unique from all the other planets in our solar system because it is the only planet in our solar system to have liquid water and oceans. 24. Mars has frozen water and at one time had liquid water. 25. Venus and Earth are called sister planets because they are similar in size and density. 26.The gas giants have atmospheres of gas that cannot escape into outer space because the planets have very strong gravity. 27. The four outer planets are much larger than Earth and do not have solid surfaces. 28. Saturn’s rings are made up of chunks of ice and rock. 29. Jupiter has a thick atmosphere made up of hydrogen and helium. It has a giant red spot that is a large storm larger than planet Earth. 30. Uranus is different from most other planets because it rotates on its side. 31.Pluto is different from the other outer planets because it is rocky and has a solid surface. 32. Astronomers believe Pluto should not be called a planet because it is so small. 33. As the planets revolve around the sun, the shape of their orbits is nearly circular ellipses. 34. The asteroid belt is located between Mars and Jupiter. 35. Mars may have once had conditions needed to support life because the surface of the planet has surface patterns that look like dried streambeds. 36. The order of the planets as they revolve around the sun is as follows: Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus and Neptune. 37. The only place in our solar system that astronauts have landed on is Earth’s moon. The reason we have pictures of other planets is because we have sent unmanned probes to other planets to take pictures. 38.Mars is called the red planet because the iron in the soil has rusted and turned red. This is further evidence that Mars had liquid water at one time. 39. The vernal equinox is the beginning of spring. 40.Day and night are caused by the Earth’s rotation on its axis. 41. Gravity is the force that keeps the moon revolving around the Earth and the planets revolving around the sun. 42. Pluto has one moon like Earth. Other planets in our solar system have many more moons except for Mercury and Venus (they have none.)