1. Station #1: Life Cycles of Stars:
Background: Just like humans, stars have life cycles. Like humans they spend most of their
life as an adult or a Main Sequence Star. Also similar to humans, is that their life span is
dependent on how they live their life. If you live life on the wild side, take many risks and
abuse your body, you will not live as long as someone who has moderate lifestyle. Well if a
star begins it’s life with a great amount of mass, it will have to burn hot and fast to maintain
equilibrium. It will run out of fuel quickly and therefore die young with a traumatic explosion.
However, the average sized star will live a long life and die a quiet peaceful death.
1) Read the NASA’s article “The Life Cycles of Stars: How Supernovae Are Formed”
2) Answer the Conclusion questions on your LAB REPORT SHEET.
3) Using the article and the illustrated cards that depict different stages of a stars life,
complete the concept map by placing the cards over the correct square. In each square are
hints to help you figure out which stage of the life cycle belongs there.
4) Once you are satisfied with your concept map, copy the titles of each card in the
corresponding boxes on the concept map on your Lab Report Sheet.
5) Please restack cards neatly for the next group.
a. Which star characteristic will determine the life cycle path of that star?
b. Explain the relationship between mass and lifespan of a star.
c. Define Nebula.
4. The Life Cycles of Stars: How Supernovae Are Formed
It is very poetic to say that we are made from the dust of the stars. Amazingly, it's
also true! Much of our bodies, and our planet, are made of elements that were created
in the explosions of massive stars. Let's examine exactly how this can be.
Life Cycles of Stars
A star's life cycle is determined by its mass. The larger its mass, the shorter its life
cycle. A star's mass is determined by the amount of matter that is available in its nebula, the
giant cloud of gas and dust from which it was born. Over time, the hydrogen gas in the nebula
is pulled together by gravity and it begins to spin. As the gas spins faster, it heats up and
becomes as a protostar. Adding atoms to the center of a protostar is a process astronomers
call accretion. Because numerous reactions occur within the mass of forming star material, a
protostar is not very stable. In order to achieve life as a star, the protostar will need to
achieve and maintain equilibrium by reaching the critical temperature of 15,000,000 degrees.
If a critical temperature in the core of a protostar is not reached, it ends up as a brown
dwarf. This mass never makes “star status.” This is considered failed star! However, if a
critical temperature in the core of a protostar is reached, then nuclear fusion begins. We
identify the birth of a star as the moment that it begins fusing hydrogen in it’s core into
helium. Once fusion begins, this baby star begins to glow brightly, contracts a little, and
becomes stable. It is now a main sequence star and will remain in this stage, shining for
millions to billions of years to come. This is the stage our Sun is at right now. Average size
stars, like our sun, glow a yellow-red color. Massive Stars shine more blue-white.
As the main sequence star glows, hydrogen in its core is converted into helium by
nuclear fusion. When the hydrogen supply in the core begins to run out, and the star is no
longer generating heat by nuclear fusion, the core becomes unstable and contracts. The outer
shell of the star, which is still mostly hydrogen, starts to expand. As it expands, it cools and
glows red. The star has now reached the red giant phase if it is a low mass star or the Super
Red Giant Phase if it is a high mass star. It is red because it is cooler than it was in the main
sequence star stage and it is a giant because the outer shell has expanded outward. In the
core of the red giant and the super red giant, helium fuses into carbon. All stars evolve the
same way up to the giant phase. The amount of mass a star has determines which of the
following life cycle paths it will take from there.
5. Above Figure: The life cycle of a low mass star (left oval) and a high mass star (right oval).
The illustration above compares the different evolutionary paths low-mass stars (like
our Sun) and high-mass stars take after the giant phase. For low-mass stars (left hand side),
after the helium has fused into carbon, the core collapses again. As the core collapses,
the outer layers of the star are expelled and a planetary nebula is formed by the outer
layers. The core remains as a white dwarf and eventually cools to become a black dwarf.
On the right of the illustration is the life cycle of a massive star (10 times or more the size
of our Sun). Like low-mass stars, high-mass stars are born in nebulae and evolve and live in
the Main Sequence. However, their life cycles start to differ after the red giant phase. A
massive star will undergo a supernova explosion. If the remnant of the explosion is 1.4 to
about 3 times as massive as our Sun, it will become a neutron star. The core of a massive star
that has more than roughly 3 times the mass of our Sun after the explosion will do something
quite different. The force of gravity overcomes the nuclear forces which keep protons and
neutrons from combining. The core is thus swallowed by its own gravity. It has now become a
black hole which readily attracts any matter and energy that comes near it. What happens
between the red giant phase and the supernova explosion is described below.
From Red Giant to Supernova: The Evolutionary Path of High Mass Stars
Once stars that are 5 times or more massive than our Sun reach the red giant phase,
their core temperature increases as carbon atoms are formed from the fusion of helium
atoms. Gravity continues to pull carbon atoms together as the temperature increases and
additional fusion processes proceed, forming oxygen, nitrogen, and eventually iron.
When the core contains essentially just iron, fusion in the core ceases. This is because
iron is the most compact and stable of all the elements. It takes more energy to break up the
iron nucleus than that of any other element. Creating heavier elements through fusing of iron
thus requires an input of energy rather than the release of energy. Since energy is no longer
being radiated from the core, in less than a second, the star begins the final phase of
gravitational collapse. The core temperature rises to over 100 billion degrees as the iron
atoms are crushed together. The repulsive force between the nuclei overcomes the force of
gravity, and the core recoils out from the heart of the star in an shock wave, which we see as
a supernova explosion.
6. Station #2 Nuclear Fusion:
A star is like a gigantic nuclear furnace. The nuclear reactions inside convert hydrogen into
helium by means of a process known as nuclear fusion. It is this nuclear reaction that gives a
star its energy. Fusion takes place when the nuclei of hydrogen atoms with one proton each
fuse together to form helium atoms with two protons. A standard hydrogen atom has one
proton in its nucleus. There are two isotopes* of hydrogen, which also contain one proton, but
contain neutrons as well. Deuterium contains one neutron while Tritium contains two. Deep
within the star, A deuterium atom combines with a tritium atom. This forms a helium atom
with two protons and two neutrons. However there is an extra neutron that gets expelled. In
this process, an incredible amount of energy is released. When the star's supply of hydrogen
is used up, it begins to convert helium into oxygen and carbon. If the star is massive enough,
it will continue until it converts carbon and oxygen into neon, sodium, magnesium, sulfur and
silicon. Eventually, these elements are transformed into calcium, iron, nickel, chromium,
copper and others until iron is formed. When the core becomes primarily iron, the star's
nuclear reaction can no longer continue. This is because the temperature required to fuse
iron is much too great. The inward pressure of gravity becomes stronger than the outward
pressure of the nuclear reaction. The star collapses in on itself. What happens next depends
on the star's original mass
*Isotopes are atoms of the same element that have the same number of protons but a
different number of neutrons in their nucleus.
1) Read the Background Information.
2) Take turns with your partner to watch the two movies about Nuclear Fusion on the Laptop.
3) Assemble the 3-D puzzle of Nuclear Fusion, using the diagram above.
4) Sketch your completed diagram on your LAB REPORT SHEET using the color pencils.
5) Disassemble the puzzle for the next group.
6) Answer the conclusion questions.
1) Why is there a release of energy during nuclear fusion?
2) When a star’s supply of hydrogen is depleted, what does it convert helium into?
3) In order for fusion to occur, what is the critical temperature that must be reached?
7. Station #3: Classifying Stars by Luminosity and Size
Astronomers use the Hertzsprung Russell diagram above to plot stars according to
their surface temperature and luminosity. The vertical axis of the H-R diagram represents a
star’s luminosity or absolute magnitude. Luminosity is technically the amount of energy a star
radiates in one second, but you can think of it as how bright or how dim the star appears.
Depending upon the textbook you use, the labels on the HR diagram could be a little
different. Luminosity is a common term, as is absolute magnitude to describe the brightness
of a star. In either case, the scale is a "ratio scale" in which stars are compared to each
other based upon if they are brighter or dimmer than our Sun. Notice how our Sun has a
value of 1.
Luminosity (absolute magnitude) is different than the apparent brightness of a star
that we see with the naked eye. This is because the brightness that we interpret can be
affected by many variables such as the strength of the light emanating from the star, the
distance from us to the star and the amount and kind of obstacles between us and the star
(such as clouds.)
Also note that 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.
8. Station #3: Classifying Stars by Luminosity and Size
1) Use the cards to arrange stars labeled on the H-R diagram in decreasing size order by
placing them on the appropriate spot on the flow chart. Record your answers on your lab
2) Label each star with its Luminosity. Is Luminosity also decreasing or is it increasing?
3) Use the H-R diagram to answer the conclusion questions.
4) Restack the cards neatly for the next group.
9. Station #3: Classifying Stars by Luminosity and Size
10. Station #3: Classifying Stars by Luminosity and Size
1) Measurements indicate that a certain star has a very high luminosity (100,000 times that
of our sun) and yet has a temperature that is cooler than the sun. What can you conclude
about this observation?
A) It could be a main sequence star. B) It may be quite large.
C) This is a typical characteristic of stars. D) There must be an error in measurement.
2) Two stars of the same color are plotted on an H-R diagram. Star A is more luminous than
star B. Which one of the following statements could explain this?
A) Star A is hotter than star B. B) Star A is more distant than star B.
C) Star A appears brighter in the sky than star B. D) Star A is larger than star B.
3) If we plot many stars on an H-R diagram, all with the same luminosity but different
A) would all lie on the main sequence B) would be all over the diagram
C) would form a horizontal line D) would form a vertical line
4) The apparent brightness of an object such as a star does not depend on
A) how fast the star is moving
B) the strength of the light emanating from the star
C) the distance from us to the star
D) the amount and kind of obstacles between us and the star
5) Which of the following stars is least bright?
A) the sun B) a blue supergiant
C) a white dwarf D) a red giant
6) Which factor does not affect a stars absolute magnitude (Luminosity)?
A) The star's temperature. B) The star's size.
C) The star's distance. D) The star's shape
7) The smallest stars on a H-R diagram are found
A) at the upper left end of the main sequence
B) at the lower right end of the main sequence
C) at the upper right corner of the H-R diagram
D) at the lower left corer of the H-R diagram
8) Red giant stars have greater luminosity than our sun mainly because they are
A) hotter B) farther away
C) larger D) older
11. Station #5: Interactive HR Diagram
Are all stars the same? Not in the least! Some stars are just beginning to form in
nebulae, others are enjoying middle age along the main sequence, and some have begun to die.
The life cycle of a star can be compared to the life cycle of humans. The Hertzsprung-
Russell Diagram is a tool that shows relationships and differences between stars. It is
something of a "family portrait." It shows stars of different ages and in different stages, all
at the same time. But it is a great tool to check your understanding of the star life cycle.
In the Hertzsprung-Russell (HR) Diagram, each star is represented by a dot. There are
lots of stars out there, so there are lots of dots. The position of each dot on the diagram
tells us two things about each star: its luminosity (or absolute magnitude) and its
The vertical axis represents the star’s luminosity. Luminosity is technically the amount
of energy a star radiates in one second, but you can think of it as how bright or how dim the
star appears compared to our Sun. The horizontal axis (x-axis) represents the star’s surface
temperature. Usually this is labeled using the Kelvin temperature scale. Note how the x-axis
is deceasing in temperature.
So how do you read the HR diagram? Well, let’s look at some basic regions on it. 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.
12. Station #5: Interactive H-R Diagram
1) Complete the Interactive Lab: HR Diagram, by clicking on the diagram that looks like this:
2) Examine the five stars. How would you describe the temperature of stars: Betelgeuse,
Vega, Our Sun, Centauri B and Sirius B when compared to each other? How would you
describe the luminosity (brightness) of the stars.
3) Use the drop down menu to choose your answers. Record your data on the Lab Report
Table 1: Drop down menu choices
5) Use the H-R Diagram to answer the challenge questions.
a. Describe the relationship between temperature and luminosity of main sequence stars.
b. What type of relationship is this?
c. Graph this relationship. Make temperature the independent variable.
Very Cool Very Dim
Fairly Hot Fairly Bright
Really Hot Really Bright
13. Station #7: Light-Up H-R Diagram
1) According to the H-R diagram a, the Sun is classified as a
A) main sequence star with a temperature of approximately 4,000ºK and a luminosity of 100
B) main sequence star with a temperature of approximately 6,000ºK and a luminosity of 1
C) white dwarf star with a temperature of approximately 10,000ºK and a luminosity of 0.01
D) blue supergiant star with a temperature of approximately 20,000ºK and a luminosity of
2) What type of star is Polaris?
A) White Dwarf B) Supergiant C) Red Giant D) Main Sequence
3)Which statement describes the general relationship between the temperature and the
luminosity of main sequence stars?
A) As temperature decreases, luminosity increases.
B) As temperature decreases, luminosity remains the same.
C) As temperature increases, luminosity increases.
D) As temperature increases, luminosity remains the same.
4) The star Algol is estimated to have approximately the same luminosity as the star
Aldebaran approximately the same temperature as the Rigel. Algol is best classified as a
A) main sequence star B) red giant star
C) white dwarf star D) red dwarf star
5) Compared to other stars, the sun is
A) among the hottest stars B) among the smallest stars
C) very unique D) about average in all respects
6) Compared with our Sun, the star Betelgeuse is
A) smaller, hotter, and less luminous B) smaller, cooler, and more luminous
C) larger, hotter, and less luminous D) larger, cooler, and more luminous
7) Compared to the sun a white dwarf star is
A) hotter and larger B) hotter and smaller
C) cooler and larger D) cooler and smaller
8) What factor below usually determines whether a star will be on the main sequence?
A) age B) mass C) size D) distance from our sun.
9) In the H-R diagram, 90 percent of all stars fall
A) in the Red Dwarf region. B) in the Supergiant region.
C) among the White Dwarfs. D) on the Main Sequence
10) Compared to the sun, Polaris is
A) hotter and less luminous B) cooler and more luminous
C) the same temperature and larger D) hotter and larger
14. Station #4 Classifying Stars by Temperature and Color:
Background: A Star’s color that we see with the naked eye depends upon its surface
temperature. As materials become hotter, their color changes from:
Astronomers use the Hertzsprung Russell diagram above to plot stars according to their
surface temperature and luminosity. The horizontal axis represents the star’s surface
temperature (not the star’s core temperature – we cannot see into the core of a star, only its
surface)! Usually this is labeled using the Kelvin temperature scale. But notice: In most
graphs and diagrams, zero (or the smaller numbers) exist to the left on the diagram. This is
not the case here. On this diagram, the higher (hotter) temperatures are on the left, and the
lower (cooler) temperatures are on the right. Some HR diagrams include the color of stars as
they can be seen through filters on spectroscopes. We can use this diagram to acquire
information about stars found in familiar constellations.
15. Station #4: Classifying Stars by Temperature and Color
1) Use the cards to arrange stars labeled on the H-R diagram in increasing temperature
order by placing them on the appropriate spot on the flow chart. Record your answers on
your lab record sheet.
2) Use the colored pencils to shade in the appropriate color for each star.
3) Use the H-R diagram to answer the conclusion questions.
4) Restack the cards neatly for the next group.
16. Station #4: Classifying Stars by Temperature and Color
17. Station #4: Classifying Stars by Temperature and Color
1) A Red giant star would most likely have a temperature of
2) An astronomer can estimate the temperature of a star by observing its
3) Which star color indicates the hottest star surface temperature?
16) Small cool stars would most likely appear to be
4) Which of the following stars is hottest?
A) a red giant
B) a white dwarf
C) the sun
D) a red dwarf
5) Barnard's Star has a surface temperature of about
A) 300 ºK
B) 3000 ºK
C) 5000 ºK
D) 10,000 ºK
18. Station #6: Equilibrium, The Life Goal of a Star
In the Beginning… Accretion:
A nebula is a cloud of dust and gas, composed primarily of hydrogen (97%) and helium (3%).
Within a nebula, there are varying regions when gravity causes this dust and gas to “clump”
together. As these “clumps” gather more atoms (mass), their gravitational attraction to
other atoms increases, pulling more atoms into the “clump.” Adding atoms to the center of a
protostar is a process astronomers call accretion. Because numerous reactions occur within
the mass of forming star material, a protostar is not very stable. In order to achieve life as
a star, the protostar will need to achieve and maintain equilibrium. What is equilibrium? It is
a balance, in this case a balance between gravity pulling atoms toward the center and gas
pressure pushing heat and light away from the center. Achieving and keeping this balance is
tough to do. When a star can no longer maintain equilibrium, it dies! Equilibrium for a
protostar occurs when gas pressure equals gravity. Gravity remains constant, so what changes
the gas pressure in a protostar? Gas pressure depends upon two things to maintain it: a very
hot temperature (keep those atoms colliding!) and density (lots of atoms in a small space).
There are two options for a protostar at this point:
What happens next is a Matter of Mass!
What determines how long you will live? You could live a long full life, dying of old age
primarily because your old, tired body has worn out. You could get a disease, like cancer, and
that could impact the length of your life. You could have a heart attack, be in a car accident,
or fall off a cliff on a hiking excursion. But most people start to see health decline when
their bodies cannot maintain a good balance. Biologists call this homeostasis, which means
balance or equilibrium. .A star needs to maintain a balance too – but this balance is between
gas pressure and gravity. What do you think determines the length of life of a star? Well,
your hint is that it’s a matter of mass. What has mass got to do with it? Well, here’s some
logic to help you figure it out. If a star has a small mass, it has fewer atoms to maintain at
equilibrium. If a star has a large mass, it has more atoms to keep at equilibrium. OVER
Option 1: If a critical temperature in the core
of a protostar is not reached, it ends up a brown
dwarf. This mass never makes “star status.”
This is considered failed star!
Option 2: If a critical temperature in the core
of a protostar is reached, then nuclear fusion
begins. We identify the birth of a star as the
moment that it begins fusing hydrogen in the
core into helium Pictures from NASA - Protostar in the Eagle Nebula
19. Equilibrium: Life Goal of a Star
The star’s main goal in life is to achieve stability, or equilibrium. The term equilibrium does
not mean that there isn’t any change in the star. It just means that there is not a net overall
change in the star. In a stable star, the gas pressure pushing out from the center is equal
with the gravity pulling atoms inward to the center – when these forces are equal, the star is
at equilibrium. Once a star reaches equilibrium for the first time, it will start burning (fusing)
hydrogen into helium. This is called Nuclear Fusion.
This 5-step process works like this:
-Nuclear fusion. Gravity = gas pressure (equilibrium)
-Out of fuel.
-Fusion stops, temperature drops.
-Core contracts (gravity pulling atoms in).
-Increased temperature (more atoms, more collisions) and density in the core reinitiates
nuclear fusion, equilibrium is achieved, and the cycle begins again at step 1
Look at the diagram on the right. There are essentially
two sections of a star: the core (where fusion occurs),
and an outer gaseous shell. The core serves as the
gravitational “center” of the star. It is very hot and
very dense. The outer shell is made of hydrogen and
helium gas. This shell helps move heat from the core of
the star to the surface of the star where energy in
the form of light and heat is released into space.
20. Station #6: Equilibrium, The Life Goal of a Star
1) Read the background information (back and front)
2) Answer the challenge question on your LAB REPORT SHEET.
3) Complete the ‘Interactive Lab: See the Equilibrium Cycle in action” by clicking on yellow
link: Equilibrium Cycle to open the window on the Laptop.
4) Click the “Start here” button and read the directions in the blue pop up window, then close
the blue window.
5) Read the “Step 1: Nuclear Fusion” and highlight the arrows or the dot to indicate whether
pressure, gravity and temperature will increase, decrease or stay the same.
6) Click the “check answer” button. Repeat till the blue window reads “That’s Right!”
7) Record your answers on your LAB REPORT SHEET by circling the answers for each step.
8) Repeat this for all five steps of achieving equilibrium.
9) Close this window for the next group!
10) On your lab report sheet complete the relationship graphs using your data. Label the type
of relationship each graph represents.
11) Answer the Conclusion questions, record your answers on you lab report sheet.
Challenge Question: Do you think being bigger is better when it comes to how long a star
lives? Choose from the two following hypotheses regarding length of star life:
i) The bigger a star is, the longer it will live.
ii) The smaller a star is, the longer it will live.
Now, for whichever hypothesis you chose, write a 1-3 sentence explanation.
Decide whether the following statements are True or False:
a) The “Strength” of gravity changes throughout the battle for equilibrium in a star.
b) When temperature increases, gravity decrease.
c) When temperature, increase, gas pressure increases.
d) When gas pressure equals gravity, the star is at equilibrium.
e) When the core contracts, gas pressure will increase.
f) Increasing density at the core will gradually increase temperature at the core of the star.
g) Temperature that the core can achieve depends upon how many atomic collisions there are
at the core of the star.
HINT: You can check your answers by clicking on the yellow link: “practice quiz” on the
Equilibrium: Life Goal of a star Website.
21. Station #8: The Future of Our Sun
Hydrogen gas is the main source of fuel that powers the nuclear reactions that occur in the
Sun. But just like many sources of fuel, the hydrogen is in limited supply. As the hydrogen gas
is used up, scientists predict that the helium created as a product of earlier nuclear
reactions will begin to fuel new nuclear reactions. When this happens, the Sun is expected to
become a red giant star with a radius that would extend out past the orbit of Venus and
possibly out as far as Earth’s orbit. Earth will probably not survive this change in the Sun’s
size. But no need to worry at this time, the Sun is not expected to expand to this size for a
few billion years.
1) Read the caption under the picture and the “What’s going on?” box.
2) Watch the animation by pressing the continue button in the lower right corner.
3) Trace out the path of our Sun’s life cycle on the HR diagram on your Lab Report Sheet.
4) When the animation stops, record the time that is listed in the lower left corner.
5) Repeat steps 2-5 till it reads “restart.” Click this once for the next group.
6) Complete the Challenge question.
7) Complete the Conclusion questions.
On the diagram of the planets and the Sun’s surface in your Lab Report Sheet, draw a
vertical line to represent the inferred location of the Sun’s surface when it becomes a red
Did you know?
Solar flares are tremendous explosions on the surface of the Sun.
In a matter of just a few minutes they heat material to many
millions of degrees and release as much energy as a billion
megatons of TNT. They occur near sunspots, usually along the
dividing line (neutral line) between areas of oppositely directed
Flares release energy in many forms of the electromagnetic
spectrum. Flares are characterized by their brightness and often
‘U’ shape . Sometimes they can be so powerful that they can
disrupt cellular phone communications.
22. Station #8: The Future of Our Sun
1) The probable fate of our sun is…
A) to expand as a red giant, undergo a nova outburst and end as a white dwarf
B) to shrink to a white dwarf then eventually expand to a red giant
C) become hotter and expand into a blue supergiant
D) to become a black hole
Base the following questions on the diagram below:
2) Stars like Earth’s Sun most likely formed directly from a
A) nebula B) supernova
C) red giant D) black dwarf
3) According to the diagram, a star like Earth’s Sun will eventually
A) explode in a supernova B) become a black hole
C) change into a white dwarf D) become a neutron star
4) Stars are believed to undergo evolutionary changes over millions of years. The flowchart
above shows stages of predicted changes in the Sun. According to this flowchart, the Sun will
A) hotter and brighter in stage 3, then cooler and dimmer in stage 4
B) cooler and dimmer in stage 3, then hotter and brighter in stage 4
C) hotter and dimmer in stage 3, then cooler and brighter in stage 4
D) cooler and brighter in stage 3, then hotter and dimmer in stage 4
5) According to the diagram, the life-cycle path followed by a star is determined by the
A) mass and size B) temperature and origin
C) luminosity and color D) luminosity and structure
23. Station #7: Light-Up H-R Diagram
1) Examine the Light up H-R Diagram.
2) Using the card cut outs complete the chart below.
3) Record your answers on your Lab Report Sheet.
4) Answer the Conclusion Questions.
Property Top Left of