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Galaxies Say Thanks to the Authors Click http://www.ck12.org/saythanks (No sign in required) To access a customizable version of this book, as well as other interactive content, visit www.ck12.org CK-12 Foundation is a non-profit organization with a mission to reduce the cost of textbook materials for the K-12 market both in the U.S. and worldwide. Using an open-content, web-based collaborative model termed the FlexBook®, CK-12 intends to pioneer the generation and distribution of high-quality educational content that will serve both as core text as well as provide an adaptive environment for learning, powered through the FlexBook Platform®. Copyright © 2013 CK-12 Foundation, www.ck12.org The names “CK-12” and “CK12” and associated logos and the terms “FlexBook®” and “FlexBook Platform®” (collectively “CK-12 Marks”) are trademarks and service marks of CK-12 Foundation and are protected by federal, state, and international laws. Any form of reproduction of this book in any format or medium, in whole or in sections must include the referral attribution link http://www.ck12.org/saythanks (placed in a visible location) in addition to the following terms. Except as otherwise noted, all CK-12 Content (including CK-12 Curriculum Material) is made available to Users in accordance with the Creative Commons Attribution-Non-Commercial 3.0 Unported (CC BY-NC 3.0) License (http://creativecommons.org/ licenses/by-nc/3.0/), as amended and updated by Creative Commons from time to time (the “CC License”), which is incorporated herein by this reference. Complete terms can be found at http://www.ck12.org/terms. Printed: November 16, 2013 www.ck12.org C ONCEPT Concept 1. Galaxies 1 Galaxies Lesson 26.2: True or False Name___________________ Class______________ Date________ Write true if the statement is true or false if the statement is false. _____ 1. There are a total of about 5 million galaxies in the universe. _____ 2. Star clusters contain greater numbers of stars than galaxies do. _____ 3. The Pleiades, or Seven Sisters, is an example of a star cluster. _____ 4. Globular clusters have a lot of dust in addition to stars. _____ 5. The Andromeda Galaxy is an example of an irregular galaxy. _____ 6. The reason we can’t see many dwarf galaxies is that they are so distant. _____ 7. The Milky Way Galaxy has a disk and central bulge. _____ 8. Our solar system is at the outermost edge of our galaxy. _____ 9. Constellations are binary or multiple star systems. _____ 10. More than half of the bright stars we see in our galaxy are actually star systems. Lesson 26.2: Critical Reading Name___________________ Class______________ Date________ Read this passage based on the text and answer the questions that follow. Types of Galaxies Galaxies are the biggest groups of stars in the universe. They can contain anywhere from a few million to many billions of stars. Galaxies are divided into three types according to shape: spiral, elliptical, and irregular galaxies. • Spiral galaxies spin and appear as a rotating disk of stars and dust, with a bulge in the middle. Several spiral arms reach outward from the central bulge like the arms of a pinwheel. Spiral galaxies have lots of gas and dust. Most of their stars are young and blue in color. • Elliptical galaxies are more-or-less egg shaped. The smallest elliptical galaxies are as small as some globular clusters. The largest elliptical galaxies can contain over a trillion stars. Most stars in elliptical galaxies are reddish to yellowish in color because they are old stars. Most elliptical galaxies contain very little gas and dust because these particles have already formed into stars. • Irregular galaxies are neither elliptical nor spiral in shape. Most irregular galaxies were once spiral or elliptical galaxies that were then deformed. This may have happened by gravitational attraction to a larger galaxy or by collision with another galaxy. Dwarf galaxies are small galaxies containing only a few million or billion stars. Dwarf galaxies are the most common type of galaxies in the universe. However, because they are small, they are also dim, so we don’t see very many dwarf galaxies from Earth. Most dwarf galaxies are irregular in shape. However, there are also dwarf elliptical 1 www.ck12.org galaxies and dwarf spiral galaxies. Dwarf galaxies are often found near larger galaxies. They sometimes collide and merge with their larger neighbors. Questions 1. What are galaxies? 2. Compare and contrast spiral, elliptical, and irregular galaxies. 3. Describe dwarf galaxies. Lesson 26.2: Multiple Choice Name___________________ Class______________ Date________ Circle the letter of the correct choice. 1. Stars in an open cluster are generally a. b. c. d. red. old. from the same nebula. two of the above 2. Groups of stars that contain the greatest numbers of stars are a. b. c. d. globular clusters. open clusters. star systems. galaxies. 3. Types of galaxies by shape include a. b. c. d. dwarf galaxies. elliptical galaxies. regular galaxies. all of the above 4. Dwarf galaxies are a. b. c. d. relatively rare. not very bright. mostly spiral shaped. two of the above 5. The Milky Way Galaxy a. b. c. d. is a dwarf galaxy. is an elliptical galaxy. has spiral arms. has 1 to 2 million stars. 6. Which statement(s) about irregular galaxies is (are) true? a. b. c. d. Most were once spiral or elliptical galaxies. They became irregular when they were deformed. They were changed by gravity or a collision. all of the above 7. Globular clusters 2 www.ck12.org a. b. c. d. Concept 1. Galaxies are spherical in shape. contain mostly blue stars. have widely spaced stars. contain billions of stars. Lesson 26.2: Matching Name___________________ Class______________ Date________ Match each definition with the correct term. Definitions _____ 1. group of up to a few thousand stars held loosely together by gravity _____ 2. type of galaxy that forms a rotating disk _____ 3. group of many thousand stars held tightly together by gravity _____ 4. type of galaxy that is shaped like an egg _____ 5. type of galaxy that is most common in the universe _____ 6. any group of millions, billions, or even trillions of stars _____ 7. type of galaxy that has no definite shape Terms a. dwarf galaxy b. elliptical galaxy c. globular cluster d. irregular galaxy e. open cluster f. spiral galaxy g. galaxy Lesson 26.2: Fill in the Blank Name___________________ Class______________ Date________ Fill in the blank with the appropriate term. 1. 2. 3. 4. 5. 6. 7. Our solar system is located in the __________ Galaxy. A set of stars that are grouped closely together is called a star __________. Hundreds or thousands of stars that are grouped closely together make up a star __________. A system of two stars orbiting each other is called a(n) __________. A spiral galaxy has projections called __________. Based on its shape, the Milky Way Galaxy is classified as a(n) __________ galaxy. At the center of most galaxies is a supermassive __________. 3 www.ck12.org Lesson 26.2: Critical Writing Name___________________ Class______________ Date________ Thoroughly answer the question below. Use appropriate academic vocabulary and clear and complete sentences. Explain how scientists determined the shape of the Milky Way Galaxy, including the types of evidence they used. 4