Step 1/2: Explorations in Teaching Secondary Mathematics and Science
Title of Lesson: How Do We Classify Stars?
Length of Lesson: 50 Minutes
Grade / Topic: 6th Grade/Earth and Space Science
Source of the Lesson:
http://carterscience8.weebly.com/uploads/2/2/5/6/22560730/hr_diagram_worksheet.pdf
Appropriateness for Middle School Students: The video will keep students engaged through strong graphics,
lively sound effects, and the use of familiar places and objects on earth to represent something as abstract as
the birth of a star. The video uses a large soccer stadium as the setting for the birth of the star, which will
instantly grab many students’ attention as it relates to sports. This lesson allows students to work in groups
and gain skills regarding communication and cooperation. It is important for middle school students to work
together in groups because it allows them to express their ideas, learn from each other’s thoughts, confirm
one another’s thought processes, and combine what they know to reach a greater level of understanding. The
practice extracting information from a graph that this lesson provides is important to middle school students
as it will be necessary in both math and science classes that they will take in the future.
Concepts: Astronomers primarily classify stars according to apparent magnitude, temperature, size, and
luminosity. The temperatures of stars are measured in kelvins, with 1 K equaling -273.5 °C. A star’s surface
temperature is mostly affected by the star’s mass, and it directly affects the star’s luminosity. Star
temperatures are measured by observing their color through two different colored filters and determining the
ratio that of wavelengths. Computer models of stellar spectra are then used to create a color-temperature
relationship that can be used for a variety of stars. Higher temperatures result in higher energy, which causes
shorter wavelengths. This means the hottest stars are blue (shorter wavelengths) and the cooler stars are red
(longer wavelengths). The apparent magnitude compares the brightness of two stars according to the
equation m2-m1=2.5(logb2-logb1)=2.5log(b1/b2). It is affected by the distance of stars and thus doesn’t give an
accurate portrayal of brightness. Absolute brightness, on the other hand, is the magnitude a star would have if
it were 10 parsecs from earth. The size of a star is measured in kilometers, usually based on diameter. The
largest star in the universe is the red hypergiant VY Canis Majoris, which is 1,800 times the size of the Sun. To
understand the relationships between many of these properties, astronomers use HR Diagrams. The HR
Diagram was developed by the astronomers Ejnar Hertzsprung and Henry Norris Russell in 1913 and relates
temperature to luminosity. It provides a visual way of understanding how these factors affect the colors and
sizes of stars.
http://www.ucolick.org/~bolte/AY4_00/week4/star_temp.html
http://www.universetoday.com/25331/size-of-stars/
http://www.atnf.csiro.au/outreach/education/senior/astrophysics/stellarevolution_hrintro.html
http://science-edu.larc.nasa.gov/EDDOCS/Wavelengths_for_Colors.html
Step 1/2: Explorations in Teaching Secondary Mathematics and Science
Florida State Standards (NGSSS) with Cognitive Complexity:
Benchmark Number Benchmark Description
SC.8.E.5.5
Describe and classify specific physical properties of
stars: apparent magnitude (brightness), temperature
(color), size, and luminosity (absolute brightness).
Cognitive Complexity
Level 2: Basic
Application of Skills
and Concepts
Performance Objectives: Students will be able to:
 Interpret the HR Diagram.
 Recall the major physical properties of stars: apparent magnitude, temperature, size, and luminosity.
 Explain the relationship between a star’s temperature and color.
 Define luminosity.
Materials List and Student Handouts
 Student nametags—1 per student
 Pre and Post-Evaluation papers—1 each per student
 HR Diagram datasheets—1 per student
 Flashlights—4
 Poster/large depiction of Earth
Advance Preparations
 Print and organize pre-evaluations—16
 Print and organize post-evaluations—16
 Print and organize HR Diagram datasheets—16
 Set up PowerPoint on projector
 Pre-load YouTube video
 Ask student to sit with a partner as they enter class
 Set up poster/large depiction of Earth at the back of the room
Safety
 No safety precautions are needed for the Exploration.
Step 1/2: Explorations in Teaching Secondary Mathematics and Science
5E Lesson:
Engagement
Time: 10 minutes
What the Teacher Will Do Teacher Directions and Probing Questions Student Responses/Possible
(What the teacher says)
Misconceptions
PowerPoint Slide 1
Good morning, class! My name is
[Good morning,
______________. I hope everyone is
___________]
having a great day so far. Today, we’ll be
talking about one specific category of
objects in space, one I’m sure you’re all
somewhat familiar with. We’ll be talking
about stars!
PowerPoint Slide 2
Specifically, we’ll be talking about the
different properties of stars. We’ll learn
how scientists classify stars and the factors
that make different stars unique.
PowerPoint Slide 3
First, though, I have pre-evaluations for
Pass out Pre-Evaluations
you all to complete. It’s really important
that you all try your best on this. Write
something down, whatever you think
might possibly be the answer! You have 5
minutes to complete the assignment. This
is an individual assignment, so please work
alone. Take one sheet of paper and pass
the rest back, and be sure to write your
name at the top. I will set a timer on the
board for 6 minutes, so you can keep track
of how long you have left. When you are
done, please raise your hand and I will
collect your paper.
PowerPoint Slide 4
Before getting into the classification of
http://www.youtube.com stars, we must start from the very
/watch?v=9EnBBIx6XkM
beginning. Let’s watch an interesting video
on how stars are born!
Stop at 2:50
PowerPoint Slide 5
PowerPoint Slide 6
Now that we know where stars come
from, we can begin to learn how stars are
different from each other. Just like people,
stars have different characteristics and are
very diverse. What are some ways you
think stars might be classified by?
Stars are classified by size, temperature,
apparent magnitude (which is the
brightness we see), and luminosity (which
is the energy a star releases over a certain
Distance
Shape
[Size, temperature, apparent
magnitude, luminosity]
Step 1/2: Explorations in Teaching Secondary Mathematics and Science
time).
Exploration
Time: 19 minutes
What the Teacher Will Do Teacher Directions and Probing Questions Student Responses/Possible
Misconceptions
PowerPoint Slide 7
To see how these factors affect one
another and the overall properties of the
star, we will be looking at HR Diagrams. HR
Diagrams were created by two
astronomers, Ejnar Hertzsprung and Henry
Norris Russell, to understand the
relationship between a star’s temperature
and luminosity, which is the energy a star
gives off over a certain amount of time.
Using these graphs, we can learn a lot
about the colors, sizes, luminosity, and
temperatures of stars.
Pass out papers to
I will now pass out the diagrams and
students in the front row worksheets you will be working on with
and have them pass the
your partner, who is the person sitting
extras back
next to you. Please pass these back to the
classmates behind you.
Lets take a look at the HR Diagram
Temperature
together. What factor do we have on the
y-axis?
[Luminosity]
What factor do we have on the x-axis?
Luminosity
[Temperature]
Temperature increases
One interesting thing about the chart is
how the change in temperature is noted.
What happens to the temperature values
[Temperature decreases]
as you go along the x-axis, toward the
right?
Temperature decreases as we go along the
x-axis, which isn’t what we’re used to
seeing on graphs! This is because HR
Diagrams are log/log graphs, which is
something we won’t be getting into today.
However, when answering these
questions, it’s very important to keep in
mind that the graph goes from high to low
temperature.
Call on student who raises Let’s check out the first two questions
[What factor affects the
hand.
together! Who would like to read question color of a star?]
one for us?
Step 1/2: Explorations in Teaching Secondary Mathematics and Science
As students work on the
assignment, walk around
the room asking the
following probing
questions.
Looking at this graph and the changing of
colors, what factor affects the color of
stars?
Correct! As we can see, the color is
changing as we move from left to right, so
we have to see what factor is on the xaxis. Since temperature is on the x-axis,
temperature determines the color of stars.
Let’s look at the second question. As
luminosity increases, what happens to the
size of the star?
Luminosity is on the y-axis, and as it
increases, the sizes of the stars increase.
Please take a look at question 12. For the
chart, you will look at the given
temperature and luminosity and then look
at the HR Diagram to determine what kind
of star is being described. You will label
that star (or area of stars) with the letter
given in the chart. Then you will fill in the
color and type of star. What questions do
you have?
You will have 15 minutes to complete this
assignment, and I’ll set the timer. At this
time, please continue working through the
questions with your partner. I’ll be going
around to answer any questions you may
have. You may begin.
What color star is the coolest?
What is meant by luminosity in this
diagram?
Luminosity
[Temperature]
It stays the same.
It decreases.
[It increases]
How long do we have?
Blue
[Red]
Distance from earth
Shininess
[Energy a star gives off over
a certain amount of time]
As temperature increases, what color are
Red
the stars?
[Blue]
Explanation
Time: 7 minutes
What the Teacher Will Do Teacher Directions and Probing Questions Student Responses/Possible
Misconceptions
Alright class, if you can hear me clap once. Distance
If you can hear me clap twice. Great! You
Shininess
have all done a wonderful job learning
Color
Step 1/2: Explorations in Teaching Secondary Mathematics and Science
PowerPoint Slides 8-10
Read through slides
explaining the three
characteristics
PowerPoint Slide 11
Read through the slide
explaining apparent
magnitude
PowerPoint Slide 12
(After students have
attempted to answer the
question)
about the properties of stars from the HR
[Temperature, luminosity,
Diagram, and now we’ll take some time to size]
discuss what we’ve learned. Which of the
main properties of stars are included in HR
Diagrams?
Now we’ll go into a little more detail about
these properties.
Temperature, luminosity, and size are
three of the four major properties of stars,
and these three can be see on HR
Diagrams. What is the 4th major property,
which isn’t included on HR Diagrams?
Apparent magnitude is the last of the four
major properties of stars.
Distance between them
Weight
[Apparent magnitude]
How is luminosity different from apparent
magnitude?
Luminosity is how much it
sparkles.
In a little bit, we’ll be seeing first-hand
how luminosity is how much energy a star
gives off while apparent magnitude is how
bright stars appear from earth. Why do
you think the hottest stars are blue?
Looking at your HR Diagram, how are
luminosity and size related?
[Luminosity is how much
energy is released from the
star over a certain time, and
apparent magnitude is how
bright the star appears to
be.]
Blue gets hotter faster
Color and temperature
aren’t related
[The color is actually
determined by the
wavelength of the energy of
the star, which is a very
complicated subject you’ll
learn more about in high
school. Think of a flame. The
hottest part of a flame is
always blue, and in the same
way, the hottest stars are
always blue.
More luminosity, smaller
size
Less luminosity, larger size
Step 1/2: Explorations in Teaching Secondary Mathematics and Science
Why do you think larger stars have more
luminosity?
[The larger the size, the
more luminosity]
They are hotter
[Since they are larger, they
have more surface area to
give off light from.
Therefore, they are able to
give off more light in total]
Elaboration
Time: 7 minutes
What the Teacher Will Do Teacher Directions and Probing Questions Student Responses/Possible
Misconceptions
PowerPoint 13
Now we’re going to explore the difference
between apparent magnitude and
Select the first four
luminosity by using flashlights. I need 4
students who raise their
helpers. Who would like to volunteer?
hand.
Pass out flashlights and
Wonderful! Please come to the front and
have each of the four
I’ll give you your flashlight.
students stand a different
distance away from the
Earth poster.
Have students shine the
Each flashlight represents a star, and this
light on the poster.
poster of Earth represents the Earth. At
this time, turn on your flashlights and
shine them at Earth.
Let’s all imagine that we are on the Earth
Answers may vary,
poster, and these flashlights are stars in
depending on the names of
the night sky. Whose star has the greatest the students with flashlights.
apparent magnitude for the people on
Students should say the
Earth?
name of the student
standing closest to the
poster.
That’s right! The greatest apparent
Students may call out the
magnitude would belong to the star
names of different
closest to Earth, because it appears to be
classmates holding
the brightest. We can see that by how
flashlights.
brightly that flashlight is shining on the
poster. Now, which of these stars has the
[They all have the same
greatest luminosity?
luminosity.]
All these stars have the same luminosity!
Remember, luminosity the amount of
energy given off by a star over a certain
time. All of these flashlights are giving off
Step 1/2: Explorations in Teaching Secondary Mathematics and Science
the same amount of energy. The
DISTANCE of these stars from Earth only
affects the apparent magnitude, which is
how bright stars appear to be to us. Thank
you for your participation, and you may all
get back to your seats now.
Evaluation
Time: 7 minutes
What the Teacher Will Do Teacher Directions and Probing Questions Student Responses/Possible
Misconceptions
PowerPoint Slide 14
I will now be passing out your PostEvaluations. For the last 6 minutes of class
Pass Post-Evaluations to
I would like you to please answer these
the students in the front
few questions for me so I can see how
row and have them pass
much you have learned today.
the rest back.
When you receive your paper be sure to
put your name on it.
Do the best you can in answering every
question.
Please work individually on this
assignment.
Once you are finished with the assessment
you can raise your hand and I will come
collect it from you.
Then, sit quietly until everyone has
finished and I have dismissed class.
You may begin, and remember to work
independently.
PowerPoint Slide 15
Please raise your hand if you still have
your paper.
Collect all papers.
Now since all papers are collected, I’d like
to thank you all for being such a great
class. It’s been an honor to teach you and I
am so thankful to have had you all as
students. I wish you the best in all your
studies, and hope you have a wonderful
day!
Step 1/2: Explorations in Teaching Secondary Mathematics and Science
Name: _______________________
Pre-Evaluation
1. What type of star has the lowest luminosity and lowest temperature?
2. List three of the major physical properties of stars.
3. What color are the coldest stars?
4. What is the definition of luminosity?
Step 1/2: Explorations in Teaching Secondary Mathematics and Science
Pre-Evaluation Answer Key
1.
1. What type of star has the lowest luminosity and lowest temperature?
Main Sequence Stars
2. List three of the major physical properties of stars.
Any three of the following: Size, temperature, apparent magnitude (brightness),
luminosity
3. What color are the coldest stars?
Red
4. What is the definition of luminosity?
The amount of energy a star gives off in a certain amount of time.
Step 1/2: Explorations in Teaching Secondary Mathematics and Science
Name: _______________________
Post-Evaluation
1. What type of star has the highest luminosity and highest temperature?
2. List three of the major physical properties of stars.
3. What color are the hottest stars?
4. What is luminosity (also known as absolute magnitude)?
Step 1/2: Explorations in Teaching Secondary Mathematics and Science
Post-Evaluation Answer Key
1. What type of star has the highest luminosity and highest temperature?
Blue Giants
2. List three of the major physical properties of stars.
Any three of the following: Size, temperature, apparent magnitude (brightness),
luminosity
3. What color are the hottest stars?
Blue
4. What is luminosity (also known as absolute magnitude)?
The amount of energy a star gives off in a certain amount of time.
Step 1/2: Explorations in Teaching Secondary Mathematics and Science
Name: _______________________
HR Diagram Worksheet
Background: The Hertzsprung-Russell diagram is a graph that illustrates the relationship that exists between
the average surface temperature of stars and their absolute magnitude, which is how bright they would
appear to be if they were all the same distance away. Rather than speak of the brightness of stars, the term
“luminosity” is often used. Luminosity is a measure of how much energy leaves a star in a certain period of
time.
Sun
Answer the questions using the above HR Diagram
1. What factor affects the color of a star?
2. As luminosity increases, what happens to the size of the star?
3. What is luminosity?
Step 1/2: Explorations in Teaching Secondary Mathematics and Science
4. What is the approximate surface temperature of the sun?
5. What is the color of the stars with the highest surface temperature?
6. What is the color of the stars with the lowest surface temperature?
7. List the color of the stars from hottest to coldest:
8. What type of star has a high temperature but a low luminosity?
9. What type of star has a high temperature and a high luminosity?
10. What type of star has a low temperature but a high luminosity?
11. What type of star has a low temperature and a low luminosity?
12. Plot the stars A - E. Once plotted determine their color and type.
Letter
Temperature
Luminosity
A
7,500 k
10 -1
B
20,000 k
10 6
C
20,000 k
10 -2
D
2,500 k
10 6
E
4,500 k
10 2
Color
Type of Star
Step 1/2: Explorations in Teaching Secondary Mathematics and Science
HR Diagram Answer Key
1. Temperature
2. Size increases
3. The amount of energy that leaves a star in a certain amount of time.
4. 6,000 K
5. Blue
6. Red
7. Blue, white, yellow, orange, red
8. White dwarves.
9. Blue giants
10. Red Supergiants
11. Main sequence
12.
Letter
Temperature
Luminosity
Color
Type of Star
A
7,500 k
10 -1
Yellow
Main Sequence
B
20,000 k
10 6
Blue
Blue Giants
C
20,000 k
10 -2
White
White Dwarves
D
2,500 k
10 6
Red
Red Supergiants
E
4,500 k
10 2
Orange
Red Giants