Ebook Telescopes

Genre Nonfiction Comprehension Skill Summarize Text Features · Labels · Captions · Diagrams · Glossary Science Content Stars and Galaxies Scott Foresman Science 5.16 ì<(sk$m)=bdjgdh< +^-Ä-U-Ä-U Vocabulary black hole constellation galaxy light-year nebula supernova Extended Vocabulary concave convex infrared light pulsar quasar reflecting telescope refracting telescope by Barbara Fierman Picture Credits Every effort has been made to secure permission and provide appropriate credit for photographic material. The publisher deeply regrets any omission and pledges to correct errors called to its attention in subsequent editions. Photo locators denoted as follows: Top (T), Center (C), Bottom (B), Left (L), Right (R), Background (Bkgd). Opener: Human Space Flight/NASA; 1 Science Museum, London /DK Images; 2 Human Space Flight/NASA; 3 ©Anglo-Australian Observatory/DK Images; 5 Robin Scagell/©Galaxy Picture Library; 9 (T) Damian Peach/©Galaxy Picture Library; 10 (TR) Science Museum, London /DK Images; 11 (TL) NASA; 12 Charles Walker / Topfoto /The Image Works, Inc.; 13 John and Lisa Merrill/Corbis; 14 ©Roger Ressmeyer/Corbis; 15 ©Roger Ressmeyer/Corbis; 16 Human Space Flight/NASA; 18 (B) Lester Lefkowitz/Corbis; 19 (TR) NRAO/AUI/©Galaxy Picture Library; 21 (TR) Bob Garner/©Galaxy Picture Library; 23 NASA. Unless otherwise acknowledged, all photographs are the copyright © of Dorling Kindersley, a division of Pearson. ISBN: 0-328-13963-7 Copyright © Pearson Education, Inc. All Rights Reserved. Printed in the United States of America. This publication is protected by Copyright, and permission should be obtained from the publisher prior to any prohibited reproduction, storage in a retrieval system, or transmission in any form by any means, electronic, mechanical, photocopying, recording, or likewise. For information regarding permission(s), write to Permissions Department, Scott Foresman, 1900 East Lake Avenue, Glenview, Illinois 60025. 3 4 5 6 7 8 9 10 V010 13 12 11 10 09 08 07 06 05 What You Already Know For centuries people have been interested in events seen in the sky. They invented tools such as the astrolabe, the sextant, and the telescope, and they built observatories to help them explore the universe. Early astronomers, such as Galileo and Newton, used simple telescopes. These used mirrors and glass to make the stars appear closer. Telescopes used today are much bigger and more powerful than early ones. Radio telescopes have bowl-shaped dishes that pick up radio waves given off by distant objects in space. Space telescopes, such as the Hubble, are launched into space beyond Earth’s atmosphere, where viewing conditions are dark and clear. Our Sun is a star. It is the closest star to Earth. A star is a giant ball of very hot gases that gives off heat and light energy. A star’s size, temperature, and distance from Earth affect how bright a star looks to us, and its color tells us how hot it is. This supernova was observed through a telescope. Telescopes have allowed scientists to measure a star’s distance from Earth in light-years. A light-year is the distance light travels in one year, which is more than 9 trillion kilometers. Telescopes have also allowed scientists to observe the birth and death of stars. New stars form in a cloud of gas and dust called a nebula. When some stars are at the end of their lives, they make a gigantic explosion called a supernova. After this, stars sometimes become black holes, or points in space with so much gravity that not even light can escape them. The Sun, Earth, and the other planets in the solar system are part of a galaxy, or a huge system of stars, gases, and other material held together by gravity. Scientists divide the galaxy into eighty-eight areas called constellations. Since their invention about four hundred years ago, telescopes have helped scientists learn many new things about the night sky. Now Hubble Space Telescope 2 let’s learn more about telescopes. 3 Look Up For thousands of years, people have been fascinated by the night sky. Ancient peoples built observatories where they plotted the movements of the stars and planets. Since then, astronomers, or scientists trained to study space, have explored the stars and planets to learn more about our galaxy and beyond. The invention of the telescope in the 1600s greatly improved astronomers’ ability to study space. A telescope is an instrument that allows a viewer to observe distant objects. Since a telescope magnifies objects, viewers can observe, study, and take photographs of distant features in the night sky. Early telescopes used glass lenses or mirrors to collect and change light and focus images. This viewer uses a telescope mounted on a tripod to view and study objects in space. 4 Telescopes allow us to see the stars and planets with more detail. Without a telescope, they look just like tiny points of light. The first telescope was invented in the 1600s. It consisted of a long tube with a glass lens that gathered light at one end and an eyepiece that magnified the image at the other end. This is called a refracting telescope. It allowed people to see farther into space than ever before. But there were many more technological advances to come. An improvement on the refracting telescope was the reflecting telescope. This type of telescope used a curved mirror instead of a glass lens. It is easier to build large reflecting telescopes than large refracting telescopes. After World War II, a new type of telescope was developed. The radio telescope picked up radio waves given off by stars, planets, and other objects in space. By 1990 technology made it possible to launch telescopes out into space. This allows telescopes to deliver much clearer images because the light from distant objects does not pass through Earth’s atmosphere before entering the telescope. When light passes through the atmosphere, some of it gets blocked. This makes objects in space harder to see. Today, many types of telescopes are available. They come in different sizes, ranging from small telescopes used by viewers in their backyards to huge telescopes housed in observatories or orbiting Earth. 5 Telescope Science Telescopes work by bending light. Some telescopes do this with lenses. Light bends when it enters the glass of a lens. This is called refraction. Different types of lenses use refraction to either focus or spread out light. Convex lenses are thicker in the middle than at the edges, and their surfaces are curved like domes. A wide beam of light entering a convex lens will be focused to a very small point. Concave lenses are thicker at their edges than in their middles. Their surfaces curve inward, like bowls. They spread narrow beams of light into wider beams. A convex lens is thicker in the middle than at the edge. This type of lens focuses light. Convex mirrors reflect light in all different directions, spreading it out. Concave mirrors reflect light rays in toward their center, focusing them to a point. A concave lens is thinner in the middle and thicker at the edge. A concave lens spreads out light rays. Mirrors can also be used to focus or spread out light. They do this by reflecting light instead of bending it. Convex mirrors have a dome-shaped surface that spreads light. Picture dropping a rubber ball on an upside-down bowl. The ball would bounce outward, away from the bowl’s center. This is what happens to each ray of light that strikes a convex mirror. Concave mirrors have a surface that curves inward. They focus light. Picture dropping a rubber ball into a bowl that is sitting right-side up. The ball would bounce inward, toward the bowl’s center. This is how a concave mirror focuses light rays. 6 7 ... - tailieumienphi.vn