The Structure of the Galaxy

Activity:
The student will map various celestial objects and determine the structure and center of the Milky Way.

Science Standards:
Nature of Science and Scientific Models (Conceptual)

Objectives:

  • The student will observe that distribution of different objects in the sky.
  • The student will infer the shape of the galaxy.
  • The student will infer the direction of the galactic center.
  • Materials:

  • Overhead transparencies of all-sky constellation map (one per group)
  • Different color overhead markers
  • Photocopies of galactic object tables
  • overhead projector and screen



  • Introduction:
    In the 18th century, astronomers Thomas Wright and William Hershel conducted meticulous sky surveys which indicated that the number of stars in all directions were essentially equal (with respect to distance). From that observation, they inferred that the Sun was at the center of the Universe. Today we know that stars come in different colors, compositions, and ages. By looking at the distribution of different types of stars, we can easily see that there is a plane of new, young, and active stars that surround us. There are also old globular clusters surrounding the galactic center near Sagittarius. Galaxies far beyond the Milky Way are visible in every direction except near the galactic center where they are obscured by galactic dust.

    Directions:
    1. Using transparencies, different groups of students place marks in constellations that have the objects listed in the tables.
    2. Groups summarize their data using the overhead for the rest of the class.
    3. Students combine data from all groups on the overhead.
    4. Class discusses the three dimensional characteristics of our galaxy.
    5. Students complete the student answer sheets.
     

    Note: Some of the materials from this activity were developed by the Harvard-Smithsonian Center for Astrophysics Project STAR Philip Sadler, Project Director.

    The Nature of the Milky Way - Student Answer Sheet

    Peering up into the night sky is definitely an awesome sight. But just where are we in all of this cosmos? How might you determine where we are located in the universe?
     
     
     
     
     
     
     
     
     
     
     

    Directions: Suppose that we look for specific kinds of objects. Each group will be assigned to look at one particular kind of object. The locations of those objects are given in the attached tables 2 - 5.

    1. Make an X with a colored marker at the location of each different object . Each group will then combine their observations with other groups.
     

     _____________________________________

    Description objects listed in the attached tables.

    Table 1 This table includes the constellations in which the Milky Way shines brightest.
     

    Table 2 Nebulae These are clouds of hydrogen dust and gas which eventually form new stars. An example is the Great Orion Nebula in the Orion's Sword Belt.
     

    Table 3 Open Star Clusters These groups of several hundred stars are easily seen with binoculars. They are usually similar in age, brightness, composition, and distance. An example is the Pleiades (the Seven Sisters) in Taurus.
     

    Table 4 Globular Clusters These are old, tightly packed clusters of several hundred thousand stars. These stars are very metal poor and are made of mostly hydrogen. An example is object M13 in the constellation of Hercules.
     

    Table 5 Galaxies These objects contain several hundred billion stars. Sometimes considered island universes, the most best example in the Andromeda Galaxy which is just east of the great square of Pegasus.

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    2. In general, where are each of these found in the sky?
     
     
     

    3. Questions to ponder.

    Are the stars spread evenly around the night sky?
     
     

    Are all of these stars inhabitants of the Milky Way Galaxy or are some of them inside other galaxies? Are all stars inside galaxies?
     
     
     

    Do you think that the Earth is inside or outside the galaxy? (Why?)
     
     
     

    Do you think that we are at the center of the galaxy or off to one side? (Why?)
     
     

    How is the distribution of galaxies different than the other objects?
     
     

    Do you think that galaxies are inside or outside our galaxy?
     
     

    There is an area of the sky that appears to have no galaxies. Why might that be?
     
     

    Summarize where we are in the cosmos.
     
     
     
     
     

    INSERT Table of Objects

    FIGURE 209

    HERE
     
     
     
     

    INSERT STAR Constellation Map IMAGE

    FIGURE 210

    HERE