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Genre Comprehension Skill Text Features Science Content Nonfiction Summarize Labels Captions Diagrams Glossary Stars and Galaxies Scott Foresman Science 5.16 ì<(sk$m)=bdjgdh< +^-Ä-U-Ä-U ISBN 0-328-13963-7

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. Hubble Space Telescope Since their invention about four hundred years ago, telescopes have helped scientists learn many new things about the night sky. Now let s learn more about telescopes. 2 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. 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. 4 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

Refracting Telescopes Refracting telescopes use lenses to make images appear larger. They consist of a tube with a lens at each end. The first lens, called the objective lens, gathers and focuses light. The viewer looks through the second lens, called the eyepiece lens. It magnifies the image. The first refracting telescope was invented by a Dutch eyeglass maker in 1608. Soon after, the great astronomer Galileo Galilei built a telescope that could magnify images to twenty times their actual size. One problem with Galileo s refracting telescope was that the colors of objects would appear a little off. Another problem was that images were blurred or fuzzy. These problems were reduced by using wide, thin lenses. But the wider a lens is, the longer a telescope has to be to make it focus properly. Also, very large lenses are very heavy. If a lens is too large, it will start to bend under its own weight, which changes the shape of images. Modern refracting telescopes are far more powerful than Galileo s telescope. This diagram shows the path of light through a refracting telescope. Phases of Venus In 1610 Galileo discovered the phases of Venus with his telescope. Its phases are similar to the Moon s. Galileo was the first person to use a telescope to study the night sky. Between 1610 and 1619, he made several important discoveries. Galileo discovered that the Milky Way galaxy was made up of many stars, and that each star was at a different distance from Earth. When he observed the Sun, he saw many spots on it. When viewing the Moon, he noticed mountains and craters. At that time, people believed that the Moon was a perfectly smooth ball, and Galileo proved that it wasn t. Galileo observed four moons orbiting the planet Jupiter. He also discovered that the planets Mercury and Venus revolve around the Sun. At that time, people believed that Earth was the center of the universe. Galileo s discoveries led to his conclusion that the Sun was actually the center of the solar system. His idea was not accepted for many years. In 1613 Galileo became the first astronomer to spot the planet Neptune, which he thought was a star. It wasn t until 1846, more than two hundred years later, that scientists realized that Neptune was a planet. Galileo s many important discoveries led to the building of better and more powerful telescopes. viewer eyepiece lens magnifies the image light Objective lens collects light. 8 9

Reflecting Telescopes An English scientist, Sir Isaac Newton, discovered that the lenses of refracting telescopes split light into different colors. This made images blurry. Newton s solution to the problem was to use mirrors instead of lenses. Mirrors do not split light. The result of his work was the invention of the reflecting telescope. Newton s reflecting telescope had a concave mirror at one end of a tube and a flat, tilted mirror in the center, near the other end. Light entered one end of the telescope and traveled to the other end, where it struck the concave mirror. This mirror gathered the light and focused it on the flat, tilted mirror. The tilted mirror reflected light out through a hole in the side of the tube and into an eyepiece. large concave mirror Newton invented the first reflecting telescope. Reflecting telescopes have a large concave mirror that collects and concentrates light. A second mirror reflects the light to the user s eye. Uranus Uranus William Herschel built reflecting telescopes using Newton s design. Using a twelve-meter-long reflecting telescope, he discovered Uranus in 1781. Later he discovered two of its moons. Newton s telescope had several advantages over the refracting telescopes in use at the time. Mirrors were much easier to make than lenses. A lens must be made of very high quality glass with no bubbles in it. Also, a lens has two surfaces that must be perfectly shaped to give a clear image. A mirror has only one surface to shape and polish. Newton s telescope was also very powerful for its size. This was an advantage because large refracting telescopes did not work very well. To make a refracting telescope more powerful, the lenses had to be moved farther apart. Telescopes were built longer and longer, until some reached over forty meters! With such long telescopes it was almost impossible to keep the lenses lined up correctly. Reflecting telescopes did not have this problem. light plane mirror 10 11

Observatories In ancient times, astronomers wanted dry, warm places to sit while they observed the night sky. The ancient Greeks and Babylonians built simple buildings for viewing the stars. These buildings were the first observatories. In more recent times, observatories have been built far from cities. These locations are very dark, making it easier to see the faint light of distant stars. Some observatories are built on high mountaintops. When telescopes are built in higher locations, light travels through less of the atmosphere before reaching them. This allows more light to get to the telescopes. In the 1600s observatories were built to house refracting telescopes. The Paris Observatory, in Meudon, France, opened in 1670. In 1675 the King of England set up the Royal Greenwich Observatory in Greenwich, England. There, astronomers created star charts to help sailors navigate on the seas. In the 1800s other types of equipment, such as cameras, became important tools in observatories. By the end of the 1800s, huge refracting telescopes were being built. Special buildings with domes on top were built to house these telescopes. The Mauna Kea observatory is located on the island of Hawaii. It is the largest observatory located on a mountain s summit in the world. Mauna Kea contains thirteen telescopes, which include both optical and radio telescopes. Two of the largest optical telescopes in the world, Keck I and Keck II, are located in the observatory at Mauna Kea. Astronomers from eleven different countries operate the telescopes. Mauna Kea is actually an inactive volcano on the largest of the Hawaiian Islands. It is the highest island mountain in the world, rising 4,205 meters above sea level. The atmosphere above Mauna Kea is very dry and free of clouds. As a result, there are more clear nights there than almost anywhere else in the world. Since its location is far from cities, there are no lights to interfere with the telescopes view. The dark skies allow astronomers to view dim galaxies that lie at the edge of the universe. Mauna Kea observatory in Hawaii is built on top of a very tall mountain. Its height and clear weather provide an excellent view of the sky. This early observatory was built in India in 1726. It enabled early astronomers to study the sky with the naked eye. 12 13

Telescopes Today If more light reaches a telescope, the image will be brighter. Bigger telescopes let in more light, so bigger telescopes are better. Until the end of the 1800s, very large telescopes had been refracting telescopes. The problems of earlier refracting telescopes had been corrected by using complicated systems of lenses. But there was a limit to how large a lens could be made. Since highquality mirrors could be made larger than lenses could, reflecting telescopes became the preferred choice. The Keck telescopes in the Mauna Kea observatory in Hawaii are some of the largest reflecting telescopes in the world. Each of the Keck mirrors consists of thirty-six smaller mirrors. All together, they make up a single mirror 10 meters across. This is called a segmented mirror. Why not just build one large mirror? Small mirrors are easier to make than large ones. They are also lighter, so they don t bend under their own weight and don t change the images. The Keck telescopes in Hawaii each contain a ten-meter-wide mirror made up of thirty-six smaller mirrors. This photograph shows just one segment of the Keck telescope mirror. The two Keck telescopes are located 85 meters from each other. Using a special computer system, images from the two telescopes can be combined. This allows the two 10-meter mirrors to act as one 85-meter mirror. An even more powerful system of telescopes is the VLT, which stands for very large telescope. It is located in Atacama, Chile. The VLT is a set of four telescopes with mirrors about 8 meters across. Working together with a computer system, these telescopes are as powerful as a single telescope with a mirror 200 meters across! The VLT produces clear images and is able to record light from even very faint and remote objects in the universe. 14 15

Hubble Astronomers realized that the layers of gases in Earth s atmosphere prevented them from observing dim objects. The gases of the atmosphere block some of the very faint light coming from space. In the 1970s scientists began to design a space-based telescope that would observe space from outside of Earth s atmosphere. In 1990 the Hubble Space Telescope was launched into orbit. The Hubble is about the size of a school bus and weighs about 11 tons. It is a reflecting telescope made up of a system of mirrors that reflect light into several cameras and instruments. The primary mirror, shaped like a bowl, is 2.4 meters across and weighs about 826 kilograms. The Hubble orbits about 600 kilometers above Earth. It provides images of objects that are billions of light-years away. The images received are converted into electrical signals and sent by radio to the Hubble s control center in the United States. Computers and radio equipment turn these signals into data scientists can study. The Hubble Space Telescope captures very clear images of space. In spite of careful planning, the first images sent by the Hubble were fuzzy. Scientists discovered that the primary mirror was not exactly the right shape. It was off by just about twothousandths of a millimeter. That tiny error was enough to make the images hazy. So in December 1993, the space shuttle Endeavor was sent up to repair the mirror. It took astronauts five tries over eleven days to fix the telescope. The mission was successful, and the images sent back from the Hubble were finally clear. Since it was launched into space, the Hubble has made several important accomplishments. The Hourglass Nebula The Hourglass Nebula is a giant cloud made by a dying star as it spread into space. The eye is the star s collapsed core. This image of the Hourglass Nebula was captured by the Hubble telescope. telescope captured a better view of Mars than had ever been seen from Earth. Images from the telescope have proven that black holes really exist. They confirmed the existence of quasars, which are strange, distant objects that give off huge amounts of energy. They have also given scientists a much better idea of how stars and galaxies are born and die. The Hubble has photographed several nebulae, or clouds of gas and dust, such as the Hourglass Nebula shown here. The telescope was also able to get an outstanding view of the collision between the planet Jupiter and a giant comet. 16 17

Radio Telescopes Radio telescopes collect and measure radio waves given off by objects in space. They can produce images of objects that don t produce enough light to be seen by optical telescopes. Karl Guthe Jansky first detected radio waves from an area in the center of the Milky Way galaxy. Jansky, an American radio engineer, is considered to be the pioneer of radio astronomy. Another engineer, Gote Reber, used what he learned about Jansky s discoveries to build the first radio telescope. In a radio telescope, a bowl-shaped dish, or reflector, collects radio waves from space. The reflector focuses the waves onto an antenna that changes them into electrical signals. A receiver records the strength of these signals. Then a computer analyzes the radio waves. Computers can also make images of the information gathered by the telescope. One of the world s leading radio observatories is the Very Large Array in New Mexico. It is made up of twentyseven radio antennas arranged in the shape of a Y. Each antenna is twentyfive meters in diameter. Radio telescopes have helped astronomers learn about pulsars and quasars. Pulsars are small, dense stars that send out radio waves. The waves come in pulses, which is where the name pulsar comes from. Very large radio telescopes have been used to map the surfaces of the Moon and the planets. Scientists send radio waves into space. These waves bounce off moons, planets, and other objects. Receivers on Earth record the radio echoes that bounce back. This process is called radar mapping. Supernovas This is a radio image of the supernova Cassiopeia A. It is estimated that the supernova occurred in about 1667. Cassiopeia A is a very strong source of radio waves. The VLA, or very large array, is one of the world s largest radio telescopes. It is located about fifty miles from Socorro, New Mexico. 18 19

Astronomy at Home You have learned about the exciting discoveries astronomers have made using telescopes. But you don t need a huge radio telescope or an observatory on top of a mountain to observe the night sky. Wherever you live, you can see some stars on a clear night. The first step is to go outside and let your eyes adjust to the darkness. Keep your eyes closed and try not to look at bright lights until your eyes adjust. Make yourself comfortable try sitting in a reclining beach chair or lying on a blanket. Other items that might be helpful include a map of the constellations, a compass, and an observation diary. After you have observed the night sky and become familiar with the constellations, you might decide that you d like to see even more. The next step is to get a telescope. Different telescopes offer different advantages and disadvantages. Refracting telescopes are closed at both ends, which makes them easier to keep clean. They are usually lighter, easy to carry, and easier to set up than reflecting telescopes of about the same power. Every telescope needs a mount to hold it up. A simple tripod will help you keep your telescope steady and will allow you to follow the object you are observing. Consider getting a planisphere too. A planisphere is a circular chart that will show you which constellations can Saturn s rings are visible through even a small telescope. Galileo first observed these rings in 1610. Scientists believe that the rings are made up of bits of rock ranging in size from fine dust to huge boulders. be seen at a given time of the year. And don t forgot to record your observations you may have just discovered a new asteroid or comet! observation diary A good mount such as this tripod will help an astronomer use a telescope more easily and effectively. compass planisphere 20 21

Watching the Night Sky Telescopes have allowed astronomers to make fantastic discoveries about the universe. Since Galileo discovered that the Sun was the center of our solar system, astronomers discoveries have changed the way we think about Earth, the universe, and everything else in space. Newton s improved telescope let astronomers observe more distant, fainter objects. The invention of the radio telescope allowed scientists to learn about objects not detected by optical telescopes. The Hubble Space Telescope has brought us images of objects and events that were once obstructed by Earth s atmosphere. Scientists continue to improve telescopes. For example, the Hubble s mission is expected to end in the year 2010. Designs are being created for the NGST, the Next Generation Space Telescope. According to the plans, the primary mirror will be ten times larger than the Hubble s, and the telescope will be equipped to pick up infrared light, which is invisible to the human eye. Even small telescopes have enabled astronomers to make amazing discoveries. Amateur astronomers have discovered new asteroids circling the Sun between Mars and Jupiter. One amateur astronomer from Australia discovered thirty-five new supernovas. As long as people are fascinated by the night sky, new discoveries will continue to be made. An interest in the night sky and the proper tools will allow a viewer to see amazing sights. 22 23

Glossary concave convex infrared light pulsar quasar a shape that is thinner in the middle and thicker at the edges a shape that is thicker in the middle and thinner at the edges a type of invisible light that lies just beyond red in the spectrum of colors a star that sends out radio waves at regular intervals a distant and extremely bright starlike object in space that gives off huge amounts of energy reflecting telescope a telescope that uses mirrors to focus light refracting telescope a telescope that uses lenses to focus light What did you learn? 1. Explain the different ways in which convex and concave lenses bend light. 2. What is the advantage of the radio telescope? 3. What is a planisphere? How can it help amateur astronomers? 4. Galileo made important discoveries using his refracting telescope. Write to explain the significance of his discoveries. Include details from the book to support your answer. 5. Summarize Astronomers faced difficulties after the Hubble telescope was launched into space. Summarize the problem and how it was solved. 24