Physical Science 8th grade (1).pdf

Meteor showers when a comet nears the sun a trail of

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meteor can be seen in the night sky about every 10 minutes. Meteor showers When a comet nears the sun, a trail of dust and other debris burns off and remains in orbit around the sun. As Earth orbits the sun, it passes through this debris, creating a meteor shower as the small bits of dust burn up in the atmosphere. During a meteor shower, you can see tens and even hundreds of meteors per hour. Because Earth passes the same dust clouds from comets each year, meteor showers can be predicted with accuracy. Meteorites If a meteor is large enough to survive the passage through Earth’s atmosphere and strike the ground, it becomes a meteorite . Meteorites are thought to be fragments from collisions involving asteroids. Most meteorites weigh only a few pounds or less and cause little damage when they hit. Most fall into the oceans that cover almost three-quarters of our planet’s surface. Meteor Crater in Winslow, Ariz., is believed to have been caused by a giant, 50-meter diameter meteorite about 50,000 years ago. The Holsinger meteorite (Figure 15.8) is the largest known piece of this 300,000-ton meteorite, most of which vaporized on impact. Figure 15.8: The Holsinger meteorite is a large piece of a much larger meteorite that blasted out Meteor Crater in Arizona about 50,000 years ago. This meteorite, while no taller than your thigh, weighs 1,400 lbs. meteor - a chunk of burning rock traveling through Earth’s atmosphere. meteorite - a meteor that passes through Earth’s atmosphere and strikes the ground.
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320 U NIT 6 A STRONOMY Use the data from Table 15.1 to make a graph of surface temperature vs. distance from the sun for the nine planets. Graph the distance on the x -axis and the temperature on the y -axis. Use the average of the high and low temperatures for Mercury, Venus, Earth, and Mars. What does your graph show you about the relationship between temperature and distance from the sun? Do the planets perfectly follow this relationship? What other factors might affect the surface temperature of the planets? 15.1 Section Review 1. Do we see planets because, like the sun, they are sources of light? 2. Name the planets in order, starting nearest to the sun. 3. What is an astronomical unit? 4. Gravitational force gets weaker as _____ increases and gets stronger as the _____ of the objects increases. 5. Gravity exists between all objects with mass. So why is it that you don’t you notice the force of gravity between you and all of the objects around you? 6. Is a satellite orbiting Earth free from Earth’s gravity? Why or why not? 7. Which planet is neither a gas planet nor a terrestrial planet? 8. Use Table 15.1 to answer the following questions: a. Which planet is the largest? The smallest? b. On which planet is gravity the strongest? The weakest? c. A day is the time it takes a planet to rotate once on its axis. Which planet has the longest day? The shortest day?
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