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,. -", Stars, Galaxies, and the Universe ~~. • • @ o Is the Sun a Star? • • • • o • ( •, • • • •, • • • • • • Six students were talking about tbe Sun. They had several different ideas. Here is what they said: • • • Sam: "Our Sun is just an average star made up of hot glowing gas." Juanita: "Our Sun is a huge ball of hot, glowing gas, but it is too close to us to be o • • • • • • • a star. " • • • • • Tillie: "Our Sun is one of the many stars found inside our solar system." Skeeter: "Our Sun was once a planet but is now a large burning ball." Maggie: "Our Sun is a major star. The other stars in the sky are sparks broken off from our Sun." • Diamond: "Our Sun is a sun. It's not a star. Suns are different from stars." ,• • • • • • • • • Which student do you agree with the most? Explain why you agree. • Uncovering Student Ideas in Astronomy 189 Stars, Galaxies and the Universe Is the Sun a Star? .... ' ................... ............. .................. , .......... . ~ ~ . 'dJ'f,; '~c"':' ) ,,-/ Purpose The purpose of this assessment probe is to elicit students' ideas about the Sun and stars. The probe is designed to uncover students' ideas about the nature of stars and their recognition that the Sun is an average star, but much closer to us than other stars. Related Concepts Apparent vs. actual size Solar system objects: identity Stars: brightness and distance, location, size Explanation Sam has the best idea: "Our Sun is just an average star made up of hot glowing gas." The 190 Sun is an average star. Some stars are much bigger and brighter than the Sun, and some are smaller and dimmer. The Sun looks much bigger and brighter because it is thousands of rinlCs closer to us than other stars. Administering the Probe The probe is primarily designed for students in upper elementary grades or middle school, although it can be used with students in high school as well, both to learn abour students' current thinking and to spark conversation as an introduction to a unit on stars. If students aren't sure what is meant by an average star, explain that average means average size and brightness. National Science Teachers Association ~~ ..•..~ ~~ Stars, Galaxies and the Universe Related Ideas in Benchmarks for Science Literacy (AAAS 2009) •••• ~ ••••••••••• 8 ••••••••••••••••• 5-8 Earth in the Solar System * Related Research • 3-5 The Universe "* Stars are like the Sun, some being smaller and some larger, but so far away that they look like points of light. 6-8 The Universe * The Sun is a medium-sized star located near the edge of a disc-shaped galaxy of stars, part of which can be seen as a glowing band of light that spans the sky on a * very clear night. The universe contains many billions of galaxies, and each galaxy contains many billions of stars. To the naked eye, even the closest of these galaxies is no more than a dim, fuzzy spot. . • The Sun is many thousands of ti mes closer to the Earth than any other star. Light from the Sun takes a few minutes to reach the Earth, but light from the next nearest star takes a few years to arrive. The trip to that star would take the fastest rocket thousands of years. Some distant galaxies are so far away that their light takes several billion years to reach the Earth. People on Earth, therefore, see them as they were that long ago in • the past. Related Ideas in National Science Education Standards (NRC 1996) •••••••• 0 ••••••••••• ~ ••••••••••••• K-4 Objects in the Sky • The Sun, an average star, is the central and largest body in the solar system. Colombo, Aroca, and Silva (2010) administered a questionnaire and interviewed 137 students ages 10-11 during a visit to a college observatory in Brazil. Although the students learned some information about the solar system during the visit, they were not able to develop a comprehensive view of the solar system. For example, 87% of the students thought that the Sun is a star, but only 18% thought the Sun was the only star in the solar system. • Agan (2004) interviewed high school and college students concerning their ideas about stars. Those interviewed included eight high school freshmen (ages 14-15) who had received minimal astronomy instruction in an Earth science class; rour high school juniors anu seniors (ages 16-18) who were completing a semesterlong astronomy course; and five college students (ages 18-19) who had not received any astronomy instruction in high school or college. In response to the question, "What's the closest star to Earth?" none of the Earth science students identified the Sun as the closest star to Earth; three of the five college students identified the Sun as closest to Earth, and all but one of the high school astronomy students responded that the Sun is the closest star to Earth. • Lightman, Miller, and Leadbeater (1987) conducted a telephone survey of adults (age 18 and over) and fOlUld that 55% of adults correctly identified the Sun as a star and 25% said the Sun is a planet. The remaining adults had a different explanation or no The Sun, Moon, stars, clouds, birds, and airplanes all have properties, locations, and movements that can be observed and explanation. described. * Indicates a strong match between the ideas elicited by the probe and a national standard's learning goal. 191 Uncovering Student Ideas in Astronomy --~,,~~,~~.- Stars, Galaxies and the Universe Suggestions for Instruction and Assessment • At the upper elementary level the primary focus should be on the Earth-Sun-Moon system and how their relative movements result in QUI' experience of everyday phenOlnena such as the apparent motion of the Sun's daily path in the sky, the day-night cycle, and phases of the Moon. This is also time to introduce the idea that the Sun is a star and all of the stars are suns, However, do not expect that all students will accept the idea, since the Sun appears so much bigger and brighter than the distant stars. • The research studies referenced earlier in this probe suggest that students can learn the fact that "the Sun is a star" but may not realize the full implications of that statement, because many still think that there are many stars in the solar system. Helping students develop a realistic mental model of the solar system that contains just one star should be a key goal for middle school science. • One approach, appropriate for middle school students, is to present new information about planetary systems that have been discovered around other stars. Students could begin by researching extrasolar planets at a website such as http:// planetquestjpl. nasa.gov! Having students draw what a distant planetary system might look like based on actual scientists' reports may help students recognize that each planetary system has a central starjust as our own solar system has one star, sometimes called by its Roman name, Sol. In some systems there are two (or even more stars) at the center. • Another approach, appropriate for middle and high school levels, is to have students research the history of the idea that the Sun is a star and that all of the stars in the 192 sky are distant suns. Although many early astronomers thought the stars were probably distant suns, two important lines of evidence were needed to convince everyone that it was true. One of these pieces of evidence was the first actual measurement of distance to a star showing that the stars are thousands of times farther away than the Sun. 'This discovery is discussed at the following website: http://cosmology. carnegiescience. edu!timeline!1838. The other line of evidence involved breaking starlight up into its various colors with a spectroscope, showing that the stars are made of the same elements (mostly hydrogen) as the Sun. That discovery is discussed at the following website: http://cosmology. carnegiescience. edu!timeline!1861. References Agan, L. 2004. Stellar ideas: Exploring students' understanding or .slars. Astronomy Education Review 3 (I): 77-97. http://aer.aas.org/ resDurcell laersczlv3/i1!P 77_s 1. American Association for the Advancement of Science (AAAS). 2009. Benchmarks for science literacy online. www.project2061.orglpubiications/ bsllonline Colombo, P, Jr., S. Aroca, and C. Silva. 2010. Daytime school guided visits to an astronomical observatory in Brazil. Astronomy Education Review 9 (1). http://aer.aas.orgll'esourcelllaersczl v9lil1pOI01l3_s1 Lightman, A. P, J. D. Miller, and B. J. Leadbeater. 1987. Contemporary cosmological beliefS. In Second International Seminar on Misconceptions and Educational Strategies in Science and Math- ematics, ed. J. D. Novak, 309-321. Ithaca, NY: Cornell University Press. National Research Council (NRC). 1996. National science education standards. Washington, DC: National Academies Press. National Science Teachers Association