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SummaryThis lesson introduces students to the concept of morphology, or shape/appearance. When little is known about a new object that astronomers (or any scientists, in fact) discover, the appearance of the object is the first thing to be studied, and is first used to categorize multiple objects before full understanding is gained. In this lesson, students are given a number of pictures of Messier-type objects and have to sort them into categories. Lecture then clarifies what the categories they created are. Suggested Time45 minutes to 2 hours, depending upon the speed/age of your students. PrerequisitesNone Learning OutcomesProcess/SkillsUpon successful completion of this lesson, students will
ContentUpon successful completion of this lesson, students will understand the science and astronomy concepts of
High School Frameworks
NSES A, B, D, F, G Materials
BackgroundHistorically it was very hard for astronomers to learn about the different types of objects in the night sky. Charles Messier (1730-1817) is the most famous person to start categorizing these objects. He worked for the king of France and was actually attempting to find comets - they used to believe all sorts of stories about comets, including that seeing one heralded the death of the king, so of course the king wanted to keep track of them! Through his small telescope, comets appeared as fuzzy blobs that move through the sky from one night to the next. As Messier hunted for comets though, he kept finding these other fuzzy blobs that didn't move through the sky. So he decided to start keeping track of them, and ended up with a list of some 100 objects known today as the Messier Catalog or Messier List. "Fuzzy blobs" in general are now collectively called Deep Sky Objects, and are traditionally broken into four types: Nebulae, Open Clusters, Globular Clusters, and Galaxies. These were first categorized by their appearance, as students will do in this lesson plan, and then further information about their distances, sizes, and compositions added to our knowledge about them. Nebulae (Neb)Latin for "cloud," traditionally nebulae (singular: nebula) were broken into categories based upon their appearance as emission (bright) nebulae and diffuse (dark) nebulae. More recently as we've learned the origins and destinies of nebulae, we tend to categorize them based upon what is actually happening inside. Star formation nebulae are clouds of dust and gas (mainly atomic hydrogen) that are collapsing under their own gravity to form stars in the center; sometimes parts are in the process of being blown away by internal stars. A couple famous star formation nebulae are the Orion Nebula (M42) and the Eagle Nebula (M16). Most stars form in nebulae and then drift apart through their lifetimes. (The Spitzer Space Telescope is especially good at examining objects transitioning from star formation nebulae to open clusters, and this is what Dr. Gutermuth studies.) When stars die they can form either planetary nebulae or supernova remnants. Most stars (including our own, Sol) die by calmly shrugging off their outer layers while the inner core becomes a white dwarf. Because it is an orderly process, we are left with a glowing symmetric shape, such as a ring (M57, Ring Nebula) or an hourglass (M27, Dumbbell Nebula), and because of the frequent circular shape these have acquired the misnomer of planetary nebula. Alternatively, very massive stars (NOT our own) die in an explosion called a supernova. Most of the star's mass is destructively and turbulently expelled in this process, leaving just a neutron star or black hole left of the inner parts of the original star. Because of the turbulence involved, we the ejected material becomes a chaotic tangle of threads and knots, as in the Crab Nebula (M1, the progenitor supernova was observed by the Chinese in the year 1054). Open Clusters (OC)After stars form in a nebula, their stellar winds blow away what gas didn't go into forming the central stars. Once the nebula is gone, the stars are no longer gravitationally bound and begin spreading apart in what is known as an open cluster. Open clusters can contain a few tens of thousands of stars, most of which are young and blue. Globular Clusters (GC)When our galaxy first formed some 13.6 billion years ago, many stars formed in large groups that were gravitationally bound. These globular clusters now drift around the outer edges of the galaxy in the halo, and contain hundreds of millions of old red stars each. Galaxies (Gal)Our Solar System is located in the Milky Way Galaxy, which contains at least 200 billion stars. Other galaxies are located outside our own, though this was very difficult for us to determine, measuring distance in space is hard! Edwin Hubble is famous for discovering and using red shift to measure distances to other galaxies and ending the decades long debate on the nature of galaxies. Some famous galaxies are the Large and Small Magellenic Clouds (two dwarf galaxies following the Milky Way through space), and the Andromeda Galaxy (M31, the closest significant galaxy) and its dwarf companion M32. Galaxies can be spiral, elliptical, irregular, or dwarf in shape, and some astronomers also label peculiar galaxies as those that are interacting with others. LessonIntroTeacher asks students about what is actually in the night sky. Common answers are Sun, Moon, stars, constellations, planets. Ask students if they've ever seen Hubble Space Telescope images, maybe show a few examples. Clarify that there's a lot more out there than "just" stars, including various types of groups of stars, and also dust and gas (mostly Hydrogen), and this is what makes most of the "pretty pictures" you see. Teacher explains activity, below. ActivityStudents break into groups of 2-4 and look at 10-15 pictures per group. If attached to each other, cut into separate pieces. Students arrange them so that things that look the same are grouped together. Teacher prompts students to make some 3-5 categories, and encourages students to write a table with category, names of objects in the category, and a description of the category that'll help them pick new items to go into it. Teacher should encourage students to clarify how they decided which objects go in which of their categories. Students should have results in 15-30 minutes. Different student groups will likely have similar categories, but it's ok if they're not identical. Once students have come up with categories, merge every two groups, so that you now have groups of 4-8 students. Have larger groups compare their systems of categorizing and see if they can find a way to combine their differing methods. If you had different objects in each group, you can now see how the additional objects can fit in to each group's categories. Give them another 10-15 minutes, then merge groups again if time and numbers allow. By the end of this section, you should have categories similar to the commonly accepted Messier designations of Neb, OC, GC, and Gal. If you are splitting the activity over multiple class periods, give students paperclips or envelopes so they can store their pictures as they're sorted. Whole classReturning to the whole class have them discuss how their category systems were similar or dissimilar. Teacher may focus this discussion by having groups of students write one of their categories on the board, along with which objects went into the category. Discussion should take around 15 minutes. Once the discussion settles down and the class has come to a consensus, reveal that the categories the students have come up with are very similar to those that astronomers have come up with over the last 230 years or so since Charles Messier. As described above, open clusters are those that have few stars loosely spread out, globular clusters have more stars in a tight knot, nebulae are fuzzy blobs of varying size and shape, galaxies are fuzzy blobs which are either spiral or oval. Follow-UpThe following can be done in class if time permits, or as take-home assignments.
AssessmentFormative
Summative
Accommodations for Students with Special NeedsA significant portion of this lesson relies upon typical visual ability, which may be accommodated multiple ways.
Students with ADD/ADHD can be assigned to help pass out materials, cut out objects from the paper, and collect materials when done. Students who finish early can be given additional objects to sort, can work on sub-categories, or can assist other students. Students with prior knowledge should be grouped together so as to not "give away the answers" to their groups, or encouraged to pretend that they're a historical astronomer who doesn't already know the "answer." They can also be given the task to determine sub-categories of nebulae or galaxies, or to examine the same objects in different wavelengths. In discussion, wait until students without prior knowledge have spoken before calling on those with prior knowledge. Further information
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