Why do astronomers try to count them? Each star tells us something about the size, scale and structure of the universe in which we live. We need to know the numbers to understand our place in space.

Investigation One:  The number of stars in the Milky Way Galaxy
Estimate the number of stars in the Milky Way Galaxy by comparing the salt grains in one cubic centimeter to the number of stars in the galaxy.

Materials:
     *kosher salt - 200 ml
     *cubic centimeter box pattern
     *chart paper
     *6" X 9 sheet of black construction paper, one per student

Procedure:  (primary)
    1.  Use the cubic centimeter box pattern to make a 1 cubic centimeter box. Fill the cube with kosher salt and explain that the salt grains represent stars in the sky.
    2.  Give each child a piece of black paper, and sprinkle a sample from the cube on the paper so that each child has a manageable amount to count (less than 50), using about  half the salt in the cube in all.
    3.  Ask students to group salt grains by 10 and find their total.  Record totals on chart paper.
    4.  Estimate the total in the cube from the sample, approximately 1000-1200 grains of kosher salt fill the cube.
    5.  Tell students that since there are about 200 billion stars located in the Milky Way Galaxy it would take about 200 million of the cubic centimeter boxes filled with salt to represent the number of stars in our galaxy.  This an amount would fill one large classroom.
 

Questions:
* Why is estimation important when dealing with big numbers?
* Since the Milky Way is one of billions of galaxies in the Universe, what does that tell us about the number of stars and the size of the universe?
 

Extensions
    *  Explain how The Milky Way got its name and identify and describe the different kinds of galaxies.
    *  Identify and describe the different kinds of galaxies.
     *  If you counted one number per second, how far would you get in one year?
 
 
 

Adapted from Project ASTRO Resource Notebook/ Astronomical Society of the Pacific

Investigation Two:  Counting large numbers of Stars
Develop a technique for estimating the number of stars in the Milky Way Galaxy.

Materials:
    *kosher salt (About 200 ml)
    *1 cubic centimeter box pattern (one per child)
    *1 cm graph Paper
    *scissors
    *ruler
    *tape
    *calculator
    *yard stick

Procedure: (Intermediate)
    1.  Have each student make a cubic centimeter box by folding and taping.
    2.  Fill the cubes with kosher salt.
    3.  Brainstorm techniques for finding the number of grains in the box without counting all of them.
    4.  Discuss sampling techniques and suggest using graph paper.
    6.  Distribute the salt on graph paper, so that it is evenly distributed on a portion of the paper.
    7.  Estimate grains by counting the grains in 1 sq cm. and multiplying by the total number of spaces covered.
    8.  Figure out how many cubic centimeters of salt are needed to represent the 200 billion stars out in our galaxy, and measure how much space they would take up in the classroom.

Question:
* What are the challenges in counting the number of stars in the Universe?
* What do we learn by counting the stars?

Extensions:
    *  Evaluate the accuracy of the statement, "The number of stars in the sky is more than the number of grains of sand on Earth."
  *  How many years would it take a person to count to 200 billion if he/she counted one number per second?
  *  Research Sloan Digital Sky Survey and find out how astronomers are conducting an accurate count of stars.
    *  Develop a procedure for estimating the stars in a picture of a Globular Cluster.
 
 

Investigation Three: Model the Milky Way Galaxy
Use salt grains to make a model of the Milky Way and locate our Solar System in one of the spiral arms.

Materials:
     * The Milky Way Galaxy
     *  kosher salt
     *  glitter
     *  cubic centimeter boxes or clear straws, cut to 1 1/2" length and taped at one end to hold the same amount.
     *  gold sequins, snipped into tiny pieces
     *  scissors
     *  glue stick

Procedure:  (Primary/Intermediate)
    1.  Fill the straw tubes or centimeter cube boxes with kosher salt.
    2.  Remind students that centimeter cube boxes/straws holds 1/200 billionths of the stars in the galaxy.
    3.  Show pictures and diagram of the Milky Way galaxy and locate our Solar System.
    4.  Make models of Milky Way by drawing the dense center of the galaxy and spiral arms of the Milky Way with the glue stick.
    5.  Sprinkle salt over drawing. Shake paper to distribute. Press in.
    6.  Sprinkle small amount of glitter on drawing.
    7.  Locate the Sun's place in the galaxy and mark with a fragment of gold sequin.
 
 

Questions:
*  How does the size of the Solar System compare to the size of the galaxy?
* What does the model of the galaxy tell us about the possibility that there could be other Solar Systems?
*  How would you model other views of the galaxy?
*  How much of the galaxy has been explored by spacecraft?

Extensions:
    *  Identify the different types of galaxies and model them.
    *  Add a zoom image of the Solar System to the model.
    *  Investigate the quasar at the center of the galaxy.

Materials:
     * Galactic Address Worksheets (one set per student)
     *  pencil
     *  colored pencils
     *  markers

Procedure:
    1.  Have students map their location at different scales in the Galactic Address packet.
    2.  For each address discuss the information needed to address an envelope.
    3.  Use the completed envelope at the end of the packet to zoom in and out through the scale.

Questions:

* How does your perception of size change at different scales?
* How does the galactic address help us understand the broad scope of the universe?

Adapted from Project ASTRO Resource Notebook/ Astronomical Society of the Pacific