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					                  Star Light, Star Bright. What Causes You to Glow so Bright?
                                         Teacher Edition

Teacher Note: this lab fits well between Investigate Part A and Part B in Activity 7 (pages E70-E71). I t
will help students become more comfortable with plotting and reading H-R diagrams. In addition, as they
compare the how the luminosity changes over time and see the relationship of a star’s lifecycle. The
premise of this lab is that the greater nuclear reaction results in brighter luminosity.




Goals: In this activity you will…
   Understand that luminosity is a measure of how much a star or other object emits energy
   Evaluate the relationship between the luminosity of a star and it’s lifespan.
   Understand that the luminosity of a star is relative to the amount of nuclear reaction occurring within the
      matter of the star

Think About It
As you stargazed after Part A you recorded your ideas about the relationship between the apparent brightness
and distance as it applies to stars. But scientists use the term luminosity to classify how much energy is being
emitted and that can often determine the stars brightness.
               1. What are your ideas about what creates the temperature of stars?
               2. Let’s assume all stars are the size of the sun. If all stars were the same size and distance, then
               how would temperature determine the star’s brightness?
               3. At which temperature would stars have a longer lifespan?




Activity

   1. As group develop a hypothesis on the effect of temperature on the brightness and lifespan of two glow
      stick stars, star A and star B.
   2. Using the materials below design an experiment to test your ideas. Make sure you test two different
      temperatures. Plan out your procedures and get teacher approval before you begin.

       2 glow sticks
       Ice
       water
       Thermometers
       Two beakers
       Goggles
       Gloves

       ******Safety issue – Breaking the chemical contained in the glow sticks can burn you. Please break the
       sticks only as directed by your teacher

(Teachers note: If you have access to a microwave in your room students can test a variety of
temperatures, which will enrich the class graphing experience. You will want to demonstrate how to
work the glow stick. Provide color stickers as students come to the class graph to plot their stars)

For a more guided version of this lab, students you can instruct students to follow the following
procedures:

1.) Place one glow stick into a beaker full of room temperature water. This is
your“control beaker”. You compare the glow of the other water temperatures to this one so
you can see if temperature has an effect on glow as compared to a “regular one”.
2.) Place the other glow stick into a beaker full of hot water. Record the glow and water
temperature every 15 seconds for two minutes.
3.) Now place the glow stick into a beaker full of ice water. Record the glow and water
temperature every 15 seconds for two minutes.

   a. Create a data table like the one below. One chart for each temperature you test. Make sure your record
      the beginning temperature. You should create a key using stars (*) to indicate brightness. For example,
      ****= brightest, ***= less bright, **= dim, *= dimmest.




                Time                     Temperature                          Brightness
     4. How would you describe the temperature of Star A compared to Star B? And how would you describe
   the luminosity (brightness) or Star A compared to Star B?

     5. Which glow stick stars emitted the most energy? What evidence do you have to support your statement?

    6. For each level of brightness place a sticker on the class chart. Blue for dimmest, white for dim, yellow
   for less bright, red for brightest. Align your star with the brightness compared to temperature.

    7. What patterns do you observe on the class graph? How do you think these could translate into the life
   cycle of stars?

   Teacher note: On the board or on chart paper label a chart with Luminosity on the Y axis with a
   simple range starting at the intersect going up, dimmest, dim, less bright, brightest. On the X access
   label temperature and the range can start at the hottest temperature recorded in the class to 0
   degrees. Place a sun in the middle as cool and dim.

   Check for Understanding:

   1. What factor determines the luminosity of a star?
   2. Which stars would have the longest life cycle – a cool, dim star or a bright, hot star? Explain.
   3. Where would our sun fit into the H-R diagram and why?



   Teacher resources: If you would like to follow up with representations of actual stars and their
   brightness and temperatures, you can access 100 colored labeled stars in pdf:
   http://astrobio.terc.edu/pdf/c2a3starcircles.pdf. These can be cut out and charted as well.

Teacher Background:

This lab represents a model of a star’s luminosity. To avoid a misconception you will need to discuss with the
students that the temperature is not creating a chemical reaction or a nuclear reaction, but that the atoms fusing
together is creating an increase in thermal and light energy.

The energy emitted from a star is a result of a nuclear reaction called nuclear fusion. The temperature of a star is
a result of the amount of nuclear fusion taking place. As more and more atoms fuse together, there is more
thermal energy. Light energy is one of the types of energy emitted. The more light energy emitted, the more
luminous the star.

There is a predictable relationship between the brightness and size of a star. This shows up on the HR diagram.
We know that hotter things are brighter. A hotter temperature means that more energy is radiated into space.
Bigger stars are brighter. A bigger surface area means that more energy is radiated into space.

Reading a H-R diagram. A star in the upper left corner of the diagram would be hot and bright. A star in the
upper right corner of the diagram would be cool and bright. The Sun rests approximately in the middle of the
diagram, and it is the star which we use for comparison. A star in the lower left corner of the diagram would be
hot and dim. A star in the lower right corner of the diagram would be cold and dim.
For more information about Star Life Cycles and H-R diagrams please access this website with an interactive
H-R diagram http://aspire.cosmic-ray.org/labs/star_life/hr_interactive.html



Extensions: Students can also test surface area and changes in temperature using Alka-Seltzer tablets, relating
how the size of a star could also effect the rate of reaction and its luminosity.




                  Star Light, Star Bright. What Causes You to Glow so Bright?
                                       Student Worksheet




Goals: In this activity you will…
   Understand that luminosity is a measure of how much a star or other object emits energy
   Evaluate the relationship between the luminosity of a star and it’s lifespan.
   Understand that the luminosity of a star is relative to the amount of nuclear reaction occurring within the
      matter of the star

Think About It
As you stargazed after Part A you recorded your ideas about the relationship between the apparent brightness
and distance as it applies to stars. But scientists use the term luminosity to classify how much energy is being
emitted and that can often determine the stars brightness.
               1. What are your ideas about what creates the temperature of stars?
               2. Let’s assume all stars are the size of the sun. If all stars were the same size and distance, then
               how would temperature determine the star’s brightness?
               3. At which temperature would stars have a longer lifespan?
Activity

   3. As group develop a hypothesis on the effect of temperature on the brightness and lifespan of two glow
      stick stars, star A and star B.
   4. Using the materials below design an experiment to test your ideas. Make sure you test two different
      temperatures. Plan out your procedures and get teacher approval before you begin.

       2 glow sticks
       Ice
       water
       Thermometers
       Two beakers
       Goggles
       Gloves

       ******Safety issue – Breaking the chemical contained in the glow sticks can burn you. Please break the
       sticks only as directed by your teacher



1.) Place one glow stick into a beaker full of room temperature water. This is
your“control beaker”. You compare the glow of the other water temperatures to this one so
you can see if temperature has an effect on glow as compared to a “regular one”.
2.) Place the other glow stick into a beaker full of hot water. Record the glow and water
temperature every 15 seconds for two minutes.
3.) Now place the glow stick into a beaker full of ice water. Record the glow and water
temperature every 15 seconds for two minutes.

   a. Create a data table like the one below. One chart for each temperature you test. Make sure your record
      the beginning temperature. You should create a key using stars (*) to indicate brightness. For example,
      ****= brightest, ***= less bright, **= dim, *= dimmest.

                Time                     Temperature                          Brightness
  4. How would you describe the temperature of Star A compared to Star B? And how would you describe
the luminosity (brightness) or Star A compared to Star B?

 5. Which glow stick stars emitted the most energy? What evidence do you have to support your statement?

 6. For each level of brightness place a sticker on the class chart. Blue for dimmest, white for dim, yellow
for less bright, red for brightest. Align your star with the brightness compared to temperature.

 7. What patterns do you observe on the class graph? How do you think these could translate into the life
cycle of stars?



Check for Understanding:

1. What factor determines the luminosity of a star?

2. Which stars would have the longest life cycle – a cool, dim star or a bright, hot star? Explain.

3. Where would our sun fit into the H-R diagram and why?

				
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