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Student Lesson Classifying Galaxies Start of Lesson What is a galaxy? A galaxy is made of billions of stars, dust, and gas all held together by gravity. Galaxies are scattered throughout the Universe. They vary greatly in size and shape. Not all galaxies look alike. This is a galaxy. This is a galaxy. http://world.smv.mus.va.us/~hastings/student2.htm (1 of 6) [5/25/1999 12:33:53 PM] Student Lesson This is also a galaxy Did you notice that these galaxy pictures don't look alike? When telescopes led to the discovery of galaxies, astronomers observed many differences. In 1926, an astronomer named Edwin Hubble decided to classify the galaxies, grouping them according to some logical scheme. He could have classified them according to color, because galaxies are different colors. You can see many different colored galaxies in the Hubble Deep Field image. He could have classified them according to size, calling small galaxies "dwarf galaxies" and calling large galaxies "massive galaxies". After considering different schemes, he decided to arrange or group them by shapes. He would classify them according to the way they looked. In science, the study of something according to its form or structure is called "morphology".g galaxy galaxy galaxy galaxy galaxy galaxy galaxy galaxy galaxy galaxyLet's consider the three galaxies we saw earlier. They are typical of the three main types of galaxies that Hubble classified. The first type of galaxy you saw is an elliptical galaxy. The word elliptical refers to its degree of "roundness". Hubble used the letter "E" to stand for elliptical galaxies. To see elliptical galaxies, click on the Galaxy Guide. http://world.smv.mus.va.us/~hastings/student2.htm (2 of 6) [5/25/1999 12:33:53 PM] Student Lesson Galaxy Guide by Josh Kennedy galaxy galaxy glalxy galaxy galaxy galaxy galaxy galaxy galaxy galaxy galaxy galaxy galaxy galaxy galaxy galaxy galaxy galaxy galaxy galaxy galaxy galaxy galaxy galaxy galaxy galaxy Hubble called the second type of galaxy you saw a spiral galaxy. It reminded him of a pinwheel or whirlpool. He used the letter "S" to stand for spiral galaxies. To see spiral galaxies, click the Galaxy Guide. galaxy galaxy glalxy galaxy galaxy galaxy galaxy galaxy galaxy galaxy galaxy galaxy galaxy galaxy galaxygalaxy galaxy galaxy galaxy galaxy galaxy galaxy galaxy galaxy galaxy galaxy The third type of galaxy reminded Hubble of a spiral with a solid bar across the center. He called it a barred spiral galaxy. He used the letters "SB" to stand for barred spirals. To see barred spiral galaxies, click on the Galaxy Guide ga l Many galaxies have strange, irregualr shapes, and do not fit neatly into any of these three categories. http://world.smv.mus.va.us/~hastings/student2.htm (3 of 6) [5/25/1999 12:33:53 PM] Student Lesson To see an example of a nearby irregular galaxy, click on the Galaxy Guide. Can you name the three main types of galaxies? Did you discover that each main type is divided into smaller groups? Click here to review. To show the relationship of the galactic shapes, Edwin Hubble arranged the main types of galaxies and the sub-types into a chart that has come to be called "The Tuning Fork Diagram". The Hubble "Tuning Fork Diagram" is the simplest way to classify galaxies. When you look at a picture of a galaxy, and try to classify it, you are trying to place it on the diagram where it belongs. You have seen some pictures of galaxies in this lesson and have looked at how they were classified. Now it's time for you to classify some galaxy pictures. Are you up to the challenge? Click here. NOTE: You must have a java-enabled browser in order for the next page to work. If your browser does not work with java applets, Click here. The Hubble Telescope has looked far into space and discovered many galaxies. Travel to the Hubble Space Telescope Institute to look at an image of a newly discovered galaxy. See if you can classify it by its shape. Read the summary written below the picture to see if you were correct! Use the Back button at the top of your Web Browser to return here when you have finished your visit to Space Telescope Science Institute. Space Telescope Science Institute The Hubble Space Telescope is making frequent new http://world.smv.mus.va.us/~hastings/student2.htm (4 of 6) [5/25/1999 12:33:53 PM] Student Lesson discoveries. If you want to do more galaxy exploring at the Hubble Space Telescope Institute, Click Here Use the Back button at the top of your Web Browser to return here when you have finished your visit to Space Telescope Science Institute. Now that you have had practice at classifying galaxies according to shape, you are ready to take the challenge of becoming a member of the Hubble Deep Field Academy. Remember this picture? This image was taken by the Hubble Space Telescope in December of 1995. It shows lots of previously unknown galaxies of different colors, shapes, and sizes. Use this link to the "Cosmic Classifier" to test your new skill at classifying galaxies in the Hubble Deep Field image. Want to find out more about Edwin Hubble's Classification system? Click on the obsrvatory dome! Are you ready to go galaxy hopping on your own? Explore these astronomy links! What is this? Click on the image to find out! Something mysterious at the heart of an elliptical galaxy! http://world.smv.mus.va.us/~hastings/student2.htm (5 of 6) [5/25/1999 12:33:53 PM] Student Lesson How many galaxies can you see here? Click on the image to enlarge it. How many different galaxy classifications identify in this picture? Click you your back-arrow to come back here when you have finished. Click here for late-breaking galactic news! comments to George & Jane Hastings this page last updated November 25, 1998 http://world.smv.mus.va.us/~hastings/student2.htm (6 of 6) [5/25/1999 12:33:53 PM] Edwin Hubble at the 100 inch telescope Classifying Galaxies Edwin Hubble at the 100 inch Telescope Edwin Hubble (1889-1953) guides the exposure of a photographic plate at the Newtonian focus of the 100-inch telescope in 1923. With this telescope, Hubble measured the distances and velocities of galaxies, work which led to today's concept of an expanding Universe. According to this profound idea, the Universe began ten to twenty billion years ago with a Big Bang. The receding galaxies that Hubble observed trace the expansion of space from that dense beginning. The telescope is a mechanical masterpiece and was dedicated as an International Historical Mechanical Engineering Landmark on June 20, 1981, by the American Society of Mechanical Engineers, only the fourth such award granted in the United States. Edwin Hubble grew up in Wheaton, Illinois, a suburb of Chicago. For a complete biography, click here. Before he went on to become a famous astronomer, Edwin Hubble taught Spanish and physics as well as coached basketball at New Albany High School, Indiana, in 1914. The New Albany High School Yearbook "Vista" was dedicated to him. Look at the dedication page of the 1914 NAHS yearbook to see a picture of Coach Hubble and the winning basketball team, then use the back arrow at the top of your browser to return here. For more information about Edwin Hubble and his system of galaxy classification Click Here, then use the back arrow at the top of your browser to return here. This page last updated December 12, 1997 Return to lesson http://world.smv.mus.va.us/~hastings/edwin1.htm [5/25/1999 12:34:03 PM] Elliptical Galaxies Classifying Galaxies Elliptical Galaxies Most galaxies are elliptical. Some elliptical galaxies are nearly circular in shape. Some elliptical galaxies are extremely stretched out, flattened,or elongated. To deal with this variation, Hubble divided the "E" classification into 8 sub-groups, which he called "E0", "E1", "E2", "E3", "E4", "E5", "E6", and "E7". E0 galaxies are nearly circular in shape. E1 galaxies are stretched out a little. E2 galaxies are more elongated, E3 galaxies even more elongated or flattened, all the way up to E7 galaxies, which are extremely elongated or stretched out. Look at these examples:"E1", "E2", "E3", "E4", "E5". Return to lesson http://world.smv.mus.va.us/~hastings/elipmain.htm [5/25/1999 12:34:07 PM] Spiral Galaxies Classifying Galaxies Spiral Galaxies When you looked at elliptical galaxies you saw that as the classification numbers progressed from E1 toward E7, their appearance was more and more flattened or elongated. Edwin Hubble observed other galaxies that were elongated, but they were different from elliptical galaxies because they had bright centers. He called the bright centers of galaxies "nuclei". He noted that many galaxies with bright nuclei also had "arms" spiraling out from the middle. He called these galaxies with bright nuclei "spiral galaxies". Hubble named the galaxies that had bright nuclei but no spiral arms "S0" (S-zero) galaxies. He classified galaxies with spiral arms into three sub-groups that described how tightly the arms were wound around the nucleus. Hubble called spirals with their arms wound tightly around the nucleus, type "Sa". He called spirals with their arms less tightly wound (that is, looser and looser) "Sb" and "Sc". Here are examples of these types of spiral galaxies. Return to lesson http://world.smv.mus.va.us/~hastings/sprlmain.htm [5/25/1999 12:34:11 PM] Barred Spiral Galaxies Classifying Galaxies Barred Spirals In about a third of spiral galaxies, the arms spiral out, not from the center, but from a straight bar of stars, gas, and dust that extends from both sides of the bright nucleus.
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