Star Forge, a web-based classroom activity on star formation
Lesson Plan for the Grade 9 Science curriculum
Unit E: Space Exploration
Objectives:
By the end of this lesson, the student will be able to:
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4.
Understand where and from what material stars are formed.
Understand what conditions are required for star formation.
Understand the main elements of the star formation process.
Understand how astronomers observe and study star formation.
Required Materials:
Background material on star formation (for the teacher only)
Worksheet 1: How to make a star, 2 pages
Six sheets of white paper (at least letter-sized) and markers
Access to internet site http://spire.uleth.ca/schools/starforge/simulation/ to run the
star formation simulator
o Worksheet 2: Star Forge - simulation worksheet, 1 page
o Access to internet site http://spire.uleth.ca/schools/starforge/animation/ to show an
animated, scientific simulation of star formation
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Time: 40 – 60 minutes
Applicable Curriculum Units:
This lesson covers specifically the curriculum unit Grade 9, Science, E: Space Exploration in
the Alberta curriculum, in particular “distribution of matter in space” (Section 1 of the STS
and Knowledge Outcomes), focusing on the presence of gas and dust in interstellar space and
the process of star formation. It builds on the Grade 7 Science Unit C: Heat and Temperature
section of the Alberta curriculum, specifically the particle model of matter.
Background:
Background material for the teacher is available in the file StarFormationBackground.pdf at
http://spire.uleth.ca/schools/starforge/
http://spire.uleth.ca/
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Content:
Introduction (~ 10 minutes)
Introduce the topic of star formation by discussing the life cycle of stars 1 , starting from the
end:
In their late ages, stars enter a variety of different stages and rather dramatic things can
happen: normal stars swell up and turn into red giants, give off their outer shells and eventually
end up as dwarfs slowly getting dimmer and dimmer. Bigger stars, called Super Giants, turn
into super-dense neutron stars in a more violent way through a supernova. And, if an
extremely massive star comes to the end of its life, it may turn into a black hole.
During the prime years of a star they happily and continuously fuse hydrogen into helium. This
is the definition of a star after all: a body of gas giving off energy that derives from nuclear
fusion. Stars need a lot of hydrogen to sustain such an on-going combustion into helium.
Already after ~10% of a star’s hydrogen has been transformed into helium, it starts other
combustion processes which lead to the final stages of a star described above.
But what comes before that? How is a star born? What are stars made of? What forces are
strong enough to create a star? What kick-starts the nuclear fusion? These are good questions
that astronomers are starting to find answers for. The Star Forge classroom activity introduces
the main steps of the current model of the star formation process.
Recipe for making a star (~10 minutes)
Divide the class into six groups and hand out the two pages of Worksheet 1 to each student.
Ask each group to go through one of the steps of the star formation process and draw a
picture of that step. Support the groups in understanding the text and coming up with a
picture to draw from it. As groups finish their work, integrate the individual sheets into a
complete process. Display these pictures as a sequence so that everyone can see them. Let the
students in the six groups explain “their step” in the star formation process and their picture.
Make corrections as necessary and summarize the process. Use the displayed material for
further reference during the class.
Heat and temperature (~10 minutes)
Ask students what heat is. How can they produce heat? (Rub their hands together; pull the
brake on a bicycle; create any kind of friction to get particles moving). Remind students that
the heat of any system is equivalent to how fast particles in this system are moving. Ask
questions relating to the particle model of heat: “What would happen if you put your hand on
a hot stove element?” (Get burned) “Why would you get burned? What are the particles on the
stove element doing?” (Moving fast).
What units do you use to measure temperature? Celsius, Fahrenheit, or Kelvin are all linearly
related, but they are anchored in different ways. Canada uses the Celsius scale and scientists
Recall that it depends on the mass of a star how long it lives: The more massive the faster they burn out. So
some stars are very old and some stars are very young in comparison to the age of the universe
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often use the Kelvin scale. The Celsius scale is defined to be 0 when water freezes and 100
when water boils. Kelvin is defined to be 0 when particles are perfectly still (which is practically
impossible to achieve for any extended system) and it increments in the same way as the
Celsius scale.
Gas and dust are scattered throughout space, even far away from any stars. Just as any other
system of particles, a cloud of gas and dust has a temperature, depending on how fast the gas
and dust particles move. Ask students how the temperature of the cloud of gas and dust
changes throughout the star formation process. (Temperature starts out very cold for an
extended period of time to allow gravity to pull the cloud together; cooling mechanisms using
heavier elements and dust keep the temperature steady enough for the cloud collapse to
continue; eventually the temperature rises as the cloud becomes dense enough and nuclear
fusion starts and hydrogen turns into heavier elements)
Watching star formation happen (~5 minutes)
The temperature of the cloud of gas and dust tells us something about the star formation
process. That’s why astronomers aim to determine the temperature of regions where they
suspect star formation. But how do they do this?
What kind of instrument do you use to measure temperature? (A thermometer) How do
thermometers work? (Thermometers are often based on the fact that certain properties of
material, such as the volume of fluids or expansion of metal, depend on their temperature: The
hotter a fluid gets, the more space it uses (mercury or alcohol-based thermometer); The hotter
a metal gets, the more it extends (analog turkey thermometer). These thermometers have to be
in direct contact with what they measure in order to work well.)
Astronomers can’t stick a thermometer into the interstellar medium to see how hot it is!
Instead, they use infrared and sumillimeter detectors to measure the otherwise invisible
radiation that “cold” matter, say below a thousand degrees Celsius, gives off. Similar to the earthermometers used in hospitals, which measure the temperature on the surface of the human
ear-drum, these thermometers can measure heat remotely. Astronomers take pictures which
represent the amount of energy emitted by the dust in star forming regions and they measure
the spectral distribution of that energy to find out exactly what kind of and how many of the
heavier elements are involved in cooling off the cloud of gas and dust. The James Clerk
Maxwell Telescope, Hawaii, or the Herschel Space Observatory are examples of such farinfrared and sub-millimeter telescopes that astronomers use who are interested in star
formation 2 .
Simulate star formation (~10 minutes)
In this classroom, you cannot observe real star formation, but you can study simulated star
formation, at least the first three steps of this process. Bring up the star forge simulation
webpage. Hand out Worksheet 2 to all students to keep track of the results. Find a volunteer as
pilot of the simulation. Explain to the class that the simulation allows you to select the kind of
raw material to use and the initial temperature. When it starts, gravity acts between all particles
2
For an on-line activity on infrared imaging and how it applies to astronomy, see http://spire.uleth.ca/infrared/
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depending on the distance between them and the masses of each particle pair 3 . Challenge the
class to try and make a star with the simulator. Ask the class what they would choose as initial
temperature and which particle mix. Let the pilot run the simulation and see whether a star was
formed or not. If not, discuss why not. Was the temperature too high or too low? Was it the
right particle mix? Why not? Try again! Which settings do the students want to use next? If it
did work: Can you find another combination of initial conditions where a star is formed? Or
try and use the same conditions again.
N.B.: Even if the right conditions are selected, a star does not always form. That’s just as in
real life: Star formation may or may not occur under given conditions. Things can always go
wrong.
Summary (~5 minutes)
Summarize the process of star formation and reiterate any key points that caused confusion or
were not sufficiently covered earlier. Bring up the animated scientific simulation from the
internet. Explain that this is a real scientific simulation, essentially a much more advanced
version of the Star Forge simulator the students had just used.
Test points:
“Why would gas and dust particles, hanging out in space, start to collect and gather together?”
(Gravitational force between particles)
“Why is a lot of Hydrogen required to make a star?” (Nuclear fusion of Hydrogen atoms is
easiest to achieve. Fusion of, say, carbon nuclei would be much harder as gravity has to
overcome the electrical repulsion of the nuclei which is proportional to Q1 * Q2 and therefore
6 * 6 = 36 times stronger than for hydrogen)
“Why are heavier elements required to make a star?” (The radiate away heat to keep the
contracting cloud of gas and dust cool so that it doesn't disintegrate in the early stages of star
formation)
“What can prevent a star from forming?” (Too much heat or too much spinning and the cloud
will disintegrate)
“What is heavier, one liter of summer air or one liter of winter air?” (winter air is heavier as it
is denser as the air molecules are not moving that that fast, constantly bouncing off and
pushing one another around)
“How can you observe and study interstellar matter that hasn’t turned into a star yet?”
(Measure the far-infrared and submillimeter energy which is emitted by very cold dust and by
the heavy elements which keep the cloud of gas and dust cold)
Students can actually “see” gravity at work with this program if they use, the “heavy elements” mix: particles
don’t move in straight lines anymore as they are pulled by other particles.
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