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Earth, Moon, Sun, and Stars A Science A–Z Earth Series Word Count: 755 Earth, Moon, Sun, and Stars Written by Alyse Sweeney Visit www.sciencea-z.com www.sciencea-z.com Earth, Moon, Sun, and Stars Key elements Used in This Book The Big Idea: Earth is part of a system of fast-moving objects in space. Earth rotates on its axis, Earth revolves around the Sun, and the Moon revolves around Earth. These movements affect important aspects of our daily lives, including night and day, our calendars, the availability of light and heat, and the appearance of the Moon and the Sun in the sky. Humans have an ever-growing understanding of how the Earth, Moon, and Sun move and interact. This understanding helps us make sense of what we see in the sky, both by day and by night. An understanding of our nearby space neighborhood can also inspire future exploration deeper into space, which may someday even include the discovery of life on distant planets. Key words: air, atmosphere, calendar, circle, crescent, dark, day, Earth, energy, full moon, gas, heat, light, month, Moon, neighbor, new moon, night, orbit, phases, planet, reflect, revolve, rock, rotate, sky, space, spin, star, Sun, water, year Key comprehension skill: Cause and effect Other suitable comprehension skills: Compare and contrast; classify information; main idea and details; identify facts; elements of a genre; interpret graphs, charts, and diagrams Key reading strategy: Visualize Other suitable reading strategies: Ask and answer questions; summarize; connect to prior knowledge; using a table of contents and headings; using a glossary and bold terms Photo Credits: Front cover: © Paul Paladin/Dreamstime.com; back cover, pages 7 (bottom), 11 (Earth): © iStockphoto.com/Andrey Prokhorov; title page: © iStockphoto.com/David de Groot; page 4: © Sean White/Design Pics/Corbis; page 5: © iStockphoto.com/Fanelli Photography; page 6: © iStockphoto.com/Ewa Wysocka-Galka; page 7 (top): © iStockphoto.com/Eric Hood; pages 9 (Sun), 11 (Sun), 13 (Earth, Sun): © iStockphoto.com/George Argyropoulos; pages 9 (Earth, stars), 14 (Earth), 16 (Earth, stars), 11 (stars), 13 (stars): courtesy of NASA/GSFC; page 9 (car): © Jupiterimages Corporation; page 11 (inset): © iStockphoto.com/Jill Chen; page 12: © Cathy Yeulet/123RF; pages 14 (Moon), 16 (Moon): © iStockphoto.com/Dra Schwartz; page 15 (top): © Paul Paladin/ 123RF; page 15 (bottom left): © iStockphoto.com/Andrey Stenkin; page 15 (bottom right): © iStockphoto.com/Kativ; page 17: © iStockphoto.com/Manley620 Illustration Credit: page 8: Cende Hill/© Learning A–Z Written by Alyse Sweeney www.sciencea-z.com Earth, Moon, Sun, and Stars © Learning A–Z Written by Alyse Sweeney All rights reserved. www.sciencea-z.com Table of Contents Introduction Introduction............................. p. 4 Earth...................................... p. 6 The Sun.................................. p. 8 When we look up into the sky, we are looking into outer space. We can see the Sun, the Moon, and stars. They all seem to move very slowly Day and Night....................... p. 11 across the sky. A Year.................................. p. 13 We live on a giant ball of rock and Our Moon............................. p. 14 it because we live on it! It is also water called Earth. We don’t see moving through space. It moves Changing Shapes of the Moon.......................... p. 16 in a giant circle around the Sun. Conclusion............................ p. 17 Glossary............................... p. 18 If you stare at the sky for an hour, you might see the stars move slowly. 3 4 Mercury Jupiter Saturn Uranus Neptune Venus Earth Mars From the Sun, the planets are: Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, and Neptune. Earth Earth is where we live. It is one of From Earth, the Moon and the Sun are the biggest objects we can see in the sky. eight planets that go around the Sun. The Moon is also a ball of rock but smaller than Earth. The Moon moves in a giant circle around Earth. As Earth is the third planet from the Sun. Being this far away keeps Earth from getting too hot or too cold. Planets Earth moves around the Sun, the closer to the Sun are so hot that steel Moon moves around Earth. would melt. Planets farther away Let’s learn more about Earth, the Sun are way too cold. Earth has the and stars, and the Moon. Let’s learn right amount of heat and light for about how they move through space. plants and animals to live here. 5 6 Most of Earth is covered by water. Light turns to heat. Water is also below ground and in the air. That’s The Sun sends light to Earth. why Earth is called the water planet. Living things need water to live. They also need air. Earth has a blanket The Sun The Sun is just one of billions of stars in space. Like most stars, it is a giant of air around it. This blanket of air ball of very, very hot gas. is called the atmosphere. The Sun sends light to Earth. Light from the Sun hits Earth. It lets us see during the day. The light changes The atmosphere is made of water, oxygen, and other gases. It helps keep in heat. 7 to heat when it hits Earth. The heat rises and warms Earth’s atmosphere. Without the Sun, Earth would be dark, cold, and lifeless. 8 The Sun Sirius Pollux Arcturus Our Sun is small compared to the next-closest stars: Sirius, Pollux, and Arcturus. 109 Earths Most stars are much bigger than our Sun. The Sun looks bigger than other stars because it is much closer to Earth. But even though it is our closest star, it is still very, very far away. The Sun is so big that 109 Earths would fit across it. If you could drive to the Sun at the speed of a car on the highway, it would take about 177 years to get there! The Sun is much, much bigger than Earth. If Earth were the size of a marble, the Sun would be as big as a ball over five feet tall. The Sun is so big that one million Earths 146 million kilometers (93 million miles) would fit inside it! 9 10 Day and Night Earth is always spinning like a top, or rotating. This rotating causes day and night. When the side of Earth we are on faces the Sun, we see the Sun’s light. It is day. As we stand on a spinning Earth, the Sun looks as if it is moving across the sky. Night comes when the side of Earth we are on rotates away from the Sun. The side facing away from the Sun is dark at night. When it is daytime on our side of Earth, it is Night nighttime on the other side of Earth. Day It takes 24 hours for Earth to rotate once. That’s one day. 11 12 A Year The Earth also moves, or revolves, around the Sun in a path called an orbit. It takes 365 ¼ days for Earth to make a complete trip Four Moons would fit across Earth. Fifty Moons would fit inside Earth’s ball. around the Sun. That’s one year! Our Moon The Moon is Earth’s closest neighbor in space. It is much smaller than Earth. About 50 Moons would fit inside Earth, or four Moons across it. The Moon is much closer to Earth than the Sun. If you could drive a car to the Moon at the same speed as driving down a highway, it would Earth takes 365 ¼ days, or a year, to circle the Sun. 13 take 150 days to get there. 14 Changing Shapes of the Moon The Moon revolves around Earth just as Earth revolves around the Sun. It takes 28 days for the Moon to travel once around Earth. The Moon does not make its own The Moon seems to change shape light. The Moon shines because it as it moves. It really does not reflects the Sun’s light. We see the Moon at night and sometimes during the day. Moonlight is really sunlight bouncing off the Moon. change shape. We just see different amounts of the sunlit side as the Moon goes around Earth. The Moon takes 28 days to orbit Earth. Moon Earth New Moon 15 16 Crescent Moon 1st Quarter Full Moon 3rd Quarter Conclusion Glossary Think about a calendar. A month is a little longer than the time it takes atmospherethe blanket of air surrounding a planet, star, or moon (p. 7) Earth the Moon to go around Earth. A the planet we live on (p. 4) MoonEarth’s only natural satellite (p. 5) year is made of 12 months. In the time it takes Earth to go all the way around the Sun, the Moon goes around Earth 13 times. A year orbitthe path taken by one object in space circling around another larger object (p. 13) planetsvery large objects that travel in orbit around a star (p. 6) usually has 365 days. reflectsbounces off something like a ball bouncing off a wall (p. 15) In the time Earth makes one trip revolvesmoves in a circle around something (p. 13) around the rotatingspinning around (p. 11) Sun, Earth starslarge, faraway objects in space that make their own light (p. 8) spins 365 times. Are Sunthe star that Earth goes around (p. 8) you dizzy yet? 17 18