ECVHS Stars and The Universe Questions

CA Rev. 5/26/20201
General Science 1A
Credit 5
Rev. 5/5/21
NAME:_________________________
CREDIT 5A: STARS AND THE UNIVERSE
Learning Goals for this Credit
Communicate scientific information clearly, thoroughly and accurately.
Use mathematics to represent physical variables and their relationships to make quantitative predictions and to
solve problems.
Lesson
Title
INTRODUCTION
5.1
Observing Space
5.2
The Sun
5.3
Stars
5.4
The Universe
PERFORMANCE TASK
QUIZ
Title
Icon
Assignments
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 Connect to Essential Question
 Exploration Activity
 Reading and Questions
 Videos (optional)
 Order of Operations and Distances in Space
 Review Questions
 Connect to Prior Knowledge
 Exploration Activity
 Reading and Questions
 Videos (optional)
 Scientific Notation and the Sun
 Review Questions
 Connect to Prior Knowledge
 Exploration Activity
 Reading and Questions
 Videos (optional)
 Starquakes Hold Secrets of Stellar Evolution
 Connect to Prior Knowledge
 Exploration Activity
 Reading and Questions
 Videos (optional)
 Stars, Galaxies, and the Universe Concept Map
 Review Questions
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Student Support Icons
Description
Review
Activity
This provides the students with a reminder that they need to answer questions.
Technology
Guides students through the tasks and assignments that require the use of
technology and manipulatives.
Reading
This icon lets the students know they will be completing a reading activity.
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NAME:_________________________
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Credit Materials
Materials
Pen/Pencil
HMH Earth Science
Textbook (optional)
Packet
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Technology Needs
Internet
Computer
HMH Online Resources
(optional)
CREDIT 5A: INTRODUCTION
Read “Why Study the Universe?” and watch the video “How Big is the Universe?” below. Then answer the
essential question.
What is the Universe?
The universe is all of space and all of time. It
is all of the matter and energy from the
largest planet to the smallest atom. It
includes you, everything you see around
you, and even things you cannot see, like the
air you breathe. When we look into the night
sky we can see distant stars and planets.
These are all part of the universe as well.
The observable universe is everything we
are able to see in space, but the universe is
much larger than that. There are parts of the
universe we cannot see because light from
those areas of space have not reached us on
Earth. So, how big is the universe? Most
scientists believe the universe is infinite and
constantly expanding. How can something
be infinite and be expanding? The universe
expansion can be thought of as stretching.
As the universe “stretches” the distance
between two objects, like two stars,
increases. For example, if you draw two
dots on a deflated balloon, and then blow air
into that balloon, the distance between those two dots will increase as the balloon stretches. This constant
“stretching” is what is causing the universe to expand. Not only is the universe expanding, the rate at which it is
expanding is constantly increasing!
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NAME:_________________________
An essential question is something that allows you to explore the content of the credit. Before you answer the
question watch the video. Then answer the essential question to the best of your ability. You will revisit it at
the end of the credit to see if your answer has evolved.
Video: How Big is the Universe? (4:16)

“How Big Is the Universe?” YouTube. MinutePhysics, 25 Feb. 213. Web. 04 June 2015.
Essential Question
Do you think that the universe has a starting point and ending point? Explain your answer.
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LESSON 5.1: OBSERVING SPACE
Learning Goals for this Credit
Communicate scientific information clearly, thoroughly and accurately.
Use mathematics to represent physical variables and their relationships to make quantitative predictions and
to solve problems.
Learning Goals for this Lesson
 Describe characteristics of the universe in terms of time, distance, and organization.
 Identify the visible and nonvisible parts of the electromagnetic spectrum.
 Calculate distances in light-years.
Lesson Assignments
 Connect to Essential Question
 Exploration Activity
 Reading and Questions
 Videos (optional)
 Order of Operations and Distances in Space
 Review Questions
Engage
Connect to Essential Question
Do you think the universe has a center? Explain your answer.
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Explore
Exploration Activity
Light enables us to view the visible parts of the universe. When we gaze into the night sky, we see stars because
of the light they emit. Light travels at a speed of 300,000 kilometers (km) per second (s). In a year, light travels
9,460,000,000,000 km. This distance is known as a light-year. Light-years are used to measure vast distances in
space. Aside from the sun, the closest star to Earth is 4.2 light-years away. Below are conversions for distances.
The following problems use these conversions. Before beginning the problems on the next page, read the
example below.
1 light-year =
9,460,000,000,000 km
1.6 km = 1 mile
Example: Light travels 9,460,000,000,000 km in one year. How far is this in miles?
To solve this type of problem, set up a ratio.
𝟗, 𝟒𝟔𝟎, 𝟎𝟎𝟎, 𝟎𝟎𝟎, 𝟎𝟎𝟎 𝒌𝒎 x
𝟏 𝒎𝒊𝒍𝒆
𝟏.𝟔 𝒌𝒎
=
When we multiply across we get:
𝟗, 𝟒𝟔𝟎, 𝟎𝟎𝟎, 𝟎𝟎𝟎, 𝟎𝟎𝟎 𝒌𝒎 𝒙 𝒎𝒊𝒍𝒆𝒔
𝟏. 𝟔 𝒌𝒎
The kilometer units cancel.
𝟗, 𝟒𝟔𝟎, 𝟎𝟎𝟎, 𝟎𝟎𝟎, 𝟎𝟎𝟎 𝒌𝒎 𝒙 𝒎𝒊𝒍𝒆𝒔
𝟏. 𝟔 𝒌𝒎
Then, divide to get the answer:
𝟓, 𝟗𝟏𝟎, 𝟎𝟎𝟎, 𝟎𝟎𝟎, 𝟎𝟎𝟎 𝒎𝒊𝒍𝒆𝒔
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Use the conversion factors on the previous page to calculate the distances between objects in our solar system
and the universe. Use the example as a reference. Make sure to show your work.
1. Our sun is 92,960,000 miles from Earth. What is the distance between the sun and Earth in kilometers?
2. Mars is the closest planet to Earth. Both Mars and Earth have different orbital speeds around the sun,
but when Mars is closest to Earth it is still 55,000,000 km away. How far is this in light-years?
3. The closest star to Earth other than the sun is Alpha Centauri. It is 4.2 light-years away. How far away
is Alpha Centauri in miles? (Hint: you will need to use both conversion factors for this problem)
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Explain
As you complete the reading, answer the questions in the space provided.
Reading
What Is Astronomy?
People studied the sky long before the telescope was invented. Farmers observed changes in daylight and star
positions to track the seasons. Sailors observed stars to navigate in new places. Today, people study the sky to
learn about the universe and how it changes. The scientific study of the universe is called astronomy.
Scientists who study the universe are astronomers. Astronomers study the universe for many reasons, such as
to discover new objects in space, such as planets, stars, black holes, and nebulas, to find new energy sources by
studying how stars shine, to protect humans from possible dangers, like a collision between asteroids and Earth.
Many government organizations, like NASA, support research in astronomy. Private organizations also support
this type of research.
What Are the Characteristics of the Universe?
One branch, or area, of astronomy is cosmology. Cosmology is the study of the origin, properties, processes,
and evolution of the universe. Astronomers who study cosmology may use telescopes to observe distant objects.
They may also use math and computer models to calculate time and distance in the universe. Astronomers think
that the universe began about 13.7 billion years ago. At that time, all the matter in the universe began to expand
outward from a single, tiny point. Scientists call this expansion the big bang. Since the big bang, the universe
has expanded. In fact, the universe is expanding faster and faster. The closest part of the universe to Earth is
our solar system. The solar system includes the sun, Earth, and the other planets. It also includes smaller
objects, such as dwarf planets, asteroids, and comets. Our solar system is part of a galaxy. A galaxy is a large
collection of stars, dust, and gas held together by gravity. Our solar system is part of the Milky Way galaxy.
The universe contains billions of other galaxies. The units of measurement used on Earth are too small to
measure distances between objects in space. Astronomers use astronomical units to describe distances in the
solar system. An astronomical unit, or AU, is the average distance between Earth and the sun. This distance is
about 150 million km. Astronomers also use the speed of light to describe distances in the universe. In one
year, light travels 9,460,000,000,000 km. This distance is called a light-year. Apart from the sun, the closest
star to Earth is 4.22 light-years away. Therefore, light from this star takes 4.22 years to reach Earth.
1. Name three objects that are found in our solar system.
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How Do Astronomers Observe Space?
Light lets us observe the world around us. We can see objects in space because of light. Some objects in space,
such as stars, produce light. Other objects, such as planets, reflect light from stars. Visible light is only one form
of energy that comes from objects in space. Astronomers study different forms of energy to learn more about
the universe. Visible light is a form of energy. This energy is part of the electromagnetic spectrum. The
electromagnetic spectrum is all the wavelengths of electromagnetic radiation. Light, radio waves, and X rays
are examples of electromagnetic radiation. Electromagnetic radiation is made of waves that have fixed
wavelengths. The human eye can see only wavelengths that are in the range of visible light. White visible light
is made of different colors of light. You can see these colors when white light refracts, or bends. Light refracts
when it passes from one substance to another. For example, a rainbow appears because light passes from the air
into raindrops and back out again. During refraction, the different colors appear because each color of light has
a different wavelength. The shortest wavelengths of visible light are blue and violet. The longest wavelengths
are orange and red. Each wavelength refracts at a different angle. When white light moves from one substance
into another, the different wavelengths bend by different amounts. The differences in bending make the colors
spread apart, as shown below.
Humans cannot see electromagnetic radiation that has wavelengths outside the range of visible light. However,
certain instruments can detect, or sense, these wavelengths. The table below shows examples of invisible
wavelengths.
Wavelength
Longer than red visible light
Shorter than blue visible light
Examples (listed from shortest
wavelength to longest)
 Infrared waves
 Microwaves
 Radio waves
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Gamma rays
X-rays
Ultraviolet ray
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2. What is the electromagnetic spectrum?
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3. What color of refracted white light has the longest wavelength?
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4. Which has a longer wavelength: gamma rays or X-rays?
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Allison, Mead A., et al. “Chapter 26: Studying Space/Section 1: Viewing the Universe.” Holt McDougal Earth Science Interactive Reader, Holt McDougal, a Division
of Houghton Mifflin Harcourt Publishing Co., 2010, pp. 391-398.
Videos
If you would like to learn more about this topic, watch the videos below for more information. (Optional)
Light seconds, light years, light centuries: How to measure extreme
distances (5:29)

“Light seconds, light years, light centuries: How to measure extreme distances – Yuan-Sen Ting.” YouTube. TED-Ed, 9 Oct
2014. Web. 26 Apr 2021.
How far is a light-year? The following video will explain just how large a lightyear is and how it relates to more familiar measurements.
IDTIMWYTIM: Radiation (3:03)

“IDTIMWYTIM: Radiation.” YouTube. SciShow, 17 May 2012. Web. 30 June 2015.
What is radiation? What kinds can we detect with our eyes and
what kinds are invisible to us? This video will explain the different types of radiation found along the
electromagnetic spectrum.
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Elaborate
Order of Operations and Distances in Space
When you solve a long mathematical problem, you must complete the operations involved in a certain order.
The correct order is parentheses, exponents, multiplication, division, addition, and subtraction. Some people use
the acronym PEMDAS or the mnemonic “Please excuse my dear Aunt Sally” to remember this order (a
mnemonic is a pattern of letters or numbers used to remember something).
The rules for order of operations are summarized below:
i. Simplify groups inside parentheses. Start with the innermost group and work outward.
ii. Simplify all exponents.
iii. Perform multiplication and division in order from left to right.
iv. Perform addition and subtraction in order from left to right.
Example: Jupiter orbits the sun at an average distance of approximately 5.2 AU (astronomical units). Saturn
orbits the sun at an average distance of approximately 9.5 AU. In kilometers, how much farther is Saturn’s
orbit than Jupiter’s?
Step 1: State the problem as an equation.
1 AU = approximately 150,000,000 km
x = difference in kilometers between Saturn’s orbit and Jupiter’s orbit
x = (9.5 x 150,000,000 km) – (5.2 x 150,000,000 km)
Step 2: Simplify groups inside parentheses.
x = 1,425,000,000 – 780,000,000
Step 3: Subtract.
x= 645,000,000 km
Step 4: Write the answer.
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Saturn’s orbit is 645,000,000 km farther than Jupiter’s orbit.
Use the order of operation rules to solve the problems below. Use the example as a reference. Make sure to
show your work.
1. The closest Saturn comes to Earth is 1,277,400,000 km. The closest Jupiter comes to Earth is
628,760,000 km. In AU, how much closer does Jupiter come to Earth than Saturn? Use the equation
below to solve.
(𝟏, 𝟐𝟕𝟕, 𝟒𝟎𝟎, 𝟎𝟎𝟎 𝒌𝒎 − 𝟔𝟐𝟖, 𝟕𝟔𝟎, 𝟎𝟎𝟎 𝒌𝒎)
𝒙=
𝟏𝟓𝟎, 𝟎𝟎𝟎, 𝟎𝟎𝟎 𝒌𝒎
2. The closest Venus comes to Earth is 0.28 AU. The closest Mars comes to Earth is 0.37 AU. In
kilometers, how much closer does Venus come to Earth than Mars does?
3. Aphelion is the point in the orbit of a planet at which it is furthest from the sun. Perihelion is the point
in the orbit of a planet at which it is closest to the sun. At aphelion, Pluto is approximately 49 AU from the
sun. At perihelion, Pluto is approximately 29.5 AU from the sun. In kilometers, how much farther is Pluto
from the sun at aphelion than at perihelion?
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Allison, Mead A., et al. “Chapter 26: Studying Space/Section 1: Viewing the Universe/Math Skills Worksheet: Order of Operations and Distances in Space.” Holt
McDougal Earth Science, Holt McDougal, a Division of Houghton Mifflin Harcourt Publishing Co., 2010.
Evaluate
Review Questions
Answer the following questions.
1. What is cosmology?
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2. Explain what occurred during the big bang.
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3. Which part of the electromagnetic spectrum can be seen by humans?
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4. How is a galaxy different from a solar system?
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5. Which unit is larger: an astronomical unit (AU) or a light-year?
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LESSON 5.2: THE SUN
Learning Goals for this Credit
Communicate scientific information clearly, thoroughly and accurately.
Use mathematics to represent physical variables and their relationships to make quantitative predictions and
to solve problems.
Learning Goals for this Lesson
 Explain how the sun converts matter into energy in its core.
 Describe the layers of the sun’s interior and atmosphere.
 Use scientific notation to express large numbers.
Lesson Assignments
 Connect to Prior Knowledge
 Exploration Activity
 Reading and Questions
 Videos (optional)
 Scientific Notation and the Sun
 Review Questions
Engage
Connect to Prior Knowledge
What do you think the sun is made of?
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Explore
Exploration Activity
Scientists use bar graphs as a tool to communicate data. Bar graphs make it easier to visualize a comparison of
data values. A bar graph may be created from data in a table or data described in text. Usually, a bar graph
includes descriptions or numerical values on the x-axis and numerical values on the y-axis. Using a bar graph,
data values are visualized simply by comparing the heights of the bars. Scientists might use a bar graph like the
one below to compare the relative temperatures in different parts of the sun.
Use the bar graph above to answer the following questions.
1. How hot is the radiative zone of the sun?
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2. Which part of the sun reaches 15,000,000 °C?
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3. Which part of the sun has a temperature of about 2,000,000 °C?
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4. Approximately how hot is the sun’s corona?
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5. From the data below, create a bar graph showing the temperatures of different parts of the sun’s
atmosphere. Make sure to label all parts of your graph. Label the x-axis “Parts of Sun’s Atmosphere”
and the y-axis “Temperature (oC)”.
Part of sun’s atmosphere
Sunspot
Chromosphere (low)
Photosphere
Chromosphere (high)
Temperature (°C)
3,500
4,000
6,000
50,000
Holt McDougal. Earth Science Chapter 29 Graphing Skills Worksheet. Austin, TX: Houghton Mifflin Harcourt Publishing Company, 2010. PDF.
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Explain
As you complete the reading, answer the questions in the space provided.
Reading
What Are the Sun’s Layers?
Scientists cannot see inside the sun. They use
models to figure out what the sun’s interior is
like. They also study the sun’s surface to learn
more about the inside of the sun. The sun has
four main layers: the core, the radiative zone,
the convective zone, and the atmosphere. The
core is the sun’s center. Like the rest of the sun,
the core is made up of ionized gas. Because the
sun’s mass is so large, the gas in the core is
under a great deal of pressure. In fact, the
pressure is so great that the core is as dense as
iron. The energy produced in the core moves
through two other zones until it reaches the
sun’s atmosphere. In the radiative zone, energy
moves in the form of electromagnetic waves, or
radiation. The next layer is the convective zone.
In the convective zone, energy moves by
convection. Convection is the transfer of energy
by moving matter. In the convective zone, hot gases transfer energy to the sun’s surface. As the gases approach
the sun’s surface, they become cooler and denser. The cooler, denser gases sink to the bottom of the convective
zone, and the cycle begins again.
1. What is the main difference between the radiative zone and the convective zone?
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What Are the Layers of the Sun’s Atmosphere?
Although the sun itself is made up of gases, scientists consider the uppermost gases as the atmosphere. The
sun’s atmosphere surrounds the convective zone. The sun’s atmosphere has three layers: the photosphere, the
chromosphere, and the corona. The photosphere is the layer closest to the convective zone. It is made up of
gases that have risen from the convective zone. The photosphere gives off most of its energy in the form of
visible light. The visible light we see from Earth comes from the photosphere. The other layers of the sun’s
atmosphere are transparent. Thus, scientists sometimes refer to the photosphere as the sun’s “surface.” The
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chromosphere is the thin layer above the photosphere. It is made up of gases that glow with a reddish light.
These gases move outward from the photosphere. The corona is the outermost layer of the sun’s atmosphere.
The corona is not very dense, but its magnetic field can stop most subatomic particles from escaping into space.
However, some particles do escape into space. Some of these particles are electrons, and others are electrically
charged particles called ions. The charged particles from the corona make up the solar wind, which flows from
the sun. We cannot usually see the chromosphere or the corona from Earth. However, during a solar eclipse,
these layers become visible.
2. What layers make up the sun’s atmosphere?
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Where Does the Sun’s Energy Come From?
The sun produces energy
through a process called
nuclear fusion. During
nuclear fusion, the nuclei
of small atoms fuse, or
combine, to form larger
nuclei. Nuclear fusion
releases huge amounts of
energy. On Earth, atoms
are made of a nucleus
surrounded by electrons.
The nucleus and electrons
stay together. However,
the high temperature and
pressure in the sun’s core
cause the electrons to
separate from the nucleus.
The nuclei in the sun tend
to push away from each
other. However, the high temperature and pressure force the nuclei close enough to fuse together. The most
common form of nuclear fusion in the sun is the fusion of hydrogen into helium. This kind of nuclear fusion has
three main steps. In the first step of nuclear fusion, two hydrogen nuclei collide and fuse to form a larger
nucleus. Each hydrogen nucleus contains only one proton, which has a positive charge. When the two nuclei
fuse, one of the protons emits a particle called a positron. When the proton emits a positron, the proton changes
into a neutron. Therefore, at the end of step 1, the nucleus has one proton and one neutron. During the second
step of nuclear fusion, another proton fuses with the new nucleus. The nucleus now contains two protons and
one neutron. It is a nucleus of the element helium. During the final step of nuclear fusion, two nuclei from step
2 fuse together. As this fusion happens, two protons are released. The remaining two protons and two neutrons
are fused together. The protons and neutrons form a new nucleus of a different form of the element helium.
One of the final products of this type of nuclear fusion is a helium nucleus. The helium nucleus has about 0.7%
less mass than the hydrogen nuclei that formed it. The lost mass has been converted into energy during the
fusion process. This energy causes the sun to shine and to have a high temperature.
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3. Why does nuclear fusion happen only in the sun’s core?
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How Can Matter Change into Energy?
In 1905, Albert Einstein suggested that a small amount of matter can become a large amount of energy. This
suggestion was part of Einstein’s theory of relativity. His theory of relativity includes the equation E = mc2.
Scientists can use this equation to calculate how much energy a certain amount of matter can become. In this
equation E represents energy, m represents mass, c represents the speed of light (about 300,000 km/s). You can
see that c2 is a very large number. Therefore, even a tiny amount of mass can become a very large amount of
energy. Scientists have used Einstein’s equation to explain how the sun produces so much energy. Each second,
the sun uses nuclear fusion to change about 4 million tons of mass into energy.
What Is the Sun Made Of?
Scientists use a spectrograph to break up a star’s light into a spectrum of colors. They can use this spectrum to
figure out what elements the star is made of. Dark lines in the spectrum form when elements in the star’s outer
layers absorb certain wavelengths of light. Each element produces a unique pattern because of the wavelengths
it absorbs. Astronomers use this information to infer which elements are part of a star. In this way, scientists
have discovered that about 75% of the sun’s mass is hydrogen. About 24% of the sun’s mass is helium.
However, the sun’s spectrum shows that the sun contains small amounts of almost all chemical elements.
4. Will the amount of hydrogen in the sun increase or decrease over the next million years? Explain your
answer.
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Why Do the Sun’s Gases Move?
The gases in the sun are constantly moving. Energy from the core pushes the gases outward. The force of
gravity pulls them inward. The sun’s rotation also causes the gases to move. Because the sun is a sphere, each
point on the sun rotates at a different speed. For example, places close to the sun’s equator rotate once every
25.3 Earth days. Places near the poles take 33 Earth days to rotate once. On average, the sun rotates once every
27 days.
What Are Sunspots?
The movement of gases forms magnetic fields in the sun. These fields slow down convection in parts of the
convective zone. That means that less energy is transferred from the core to those parts of the photosphere.
Therefore, those areas are cooler than other areas of the photosphere. These cooler areas are called sunspots.
Sunspots appear darker than the photosphere around them. The rest of the photosphere has a grainy appearance,
called granulation. Astronomers have studied sunspots for hundreds of years. In fact, they discovered that the
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sun rotates by watching how sunspots move. Later, they discovered that the number and location of sunspots
change in a cycle that lasts about 11 years. At the beginning of a sunspot cycle, the number of sunspots is very
small. Slowly, more sunspots appear, especially in the area about halfway between the equator and the poles.
The number of sunspots increases every year, until there are more than 100 sunspots. Then, sunspots at higher
latitudes slowly begin to disappear, and new ones appear near the equator. Slowly, the number of sunspots
decreases, and the cycle begins again.
5. Why are sunspots cooler than the other areas of the photosphere?
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What Are Solar Eruptions?
The sun’s magnetic fields can affect the solar activity cycle, too. This cycle describes the increases and
decreases in different types of solar activity, such as solar eruptions. During a solar eruption, the sun lifts a lot
of material above the photosphere and emits tiny particles. Prominences, solar flares, and coronal mass ejections
are three examples of solar eruptions. Prominences are huge clouds of glowing gas that form arches above the
sun’s surface. The shape of the sun’s magnetic field makes prominences form huge arches. The prominences
bend to follow the sun’s magnetic field. Solar flares are the most violent of all solar eruptions. A solar flare is
a sudden eruption of electrons, protons, or other electrically charged particles. Scientists do not know what
causes solar flares. However, they do know that solar flares release the energy that is stored in a sunspot’s
magnetic field. Solar flares rarely last longer than one hour. During a peak in the sunspot cycle, 5 to 10 solar
flares may happen every day. Sometimes, the sun can throw off parts of the corona. This is called a coronal
mass ejection. Particles from a coronal mass ejection fly into space and can hit Earth’s magnetosphere. Earth’s
magnetosphere is the area around Earth that contains a magnetic field. A coronal mass ejection can disturb
Earth’s magnetic field. This disturbance is called a geomagnetic storm. Geomagnetic storms can interfere with
radio communications on Earth. They can also damage satellites or cause blackouts. A few small geomagnetic
storms happen each month. Severe geomagnetic storms happen, on average, less than once a year.
What Are Auroras?
When the solar wind interacts with Earth’s magnetosphere, auroras can form. Auroras are bands of colored
light in the sky. The particles in the solar wind are attracted to Earth’s magnetic poles. When the particles
interact with the magnetosphere, they give off light. Most auroras form near the north or south magnetic poles.
Auroras can also be called aurora borealis (northern lights) or aurora australis (southern lights).
6. How do auroras form?
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Allison, Mead A., et al. “Chapter 29: The Sun/Section 1: Structure of the Sun.” Holt McDougal Earth Science Interactive Reader, Holt McDougal, a Division of
Houghton Mifflin Harcourt Publishing Co., 2010, pp. 457-462.
Allison, Mead A., et al. “Chapter 29: The Sun/Section 2: Solar Activity.” Holt McDougal Earth Science Interactive Reader, Holt McDougal, a Division of Houghton
Mifflin Harcourt Publishing Co., 2010, pp. 463-466.
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Videos
If you would like to learn more about this topic, watch the videos below for more information. (Optional)
The Sun: Crash Course Astronomy #10 (12:03)

0
“The Sun: Crash Course Astronomy #10.” YouTube. CrashCourse, 19 Mar. 2015. Web. 01
July 2015.
Want to know more about the sun’s core, plasma, sun spots,
and solar eruptions? This video will take a closer look at
our sun and discuss how it impacts our planet.
Sun VS. Atomic Bomb (3:44)

“Sun VS. Atomic Bomb.” YouTube. SciShow, 22 Mar. 2012. Web. 01 July 2015.
How are the sun and an atomic bomb similar? This video will explain just how powerful
the nuclear fusion reactions taking place in our sun actually are.
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Elaborate
Scientific Notation and the Sun
When compared to Earth, the sun is very large and has extreme temperatures. The numbers used to describe the
sun can be large. However, by using scientific notation these numbers can be easier to read and write.
Scientific notation expresses large numbers as a number between 1 and 10 multiplied by a power of 10. For
example, scientific notation expresses 800,000 as 8  105.
A power of 10 is expressed as 10 with an exponent, or a number written above and to the right of another
number. With powers of 10, the exponent tells how many zeros follow the number one. For example:
101 is 10  1 or 10 (one zero)
102 is 10  10, or 100 (two zeros)
103 is 10  10  10, or 1,000 (three zeros).
To write a large number in scientific notation, identify the digits that are not place-holding zeros. Place a
decimal to the right of the left-most digit. To find the exponent of 10, count the number of places to the right of
the decimal point. For example, for 72,000, you would place a decimal to the right of 7 to get 7.2 (a number
between 1 and 10). The exponent of 10 would be 4, or the number of places to the right of the decimal. In
scientific notation, 72,000 equals 7.2  104.
Example: An example of a large number used in describing the sun is the temperature of some solar flares:
20,000,000 °C. Express 20,000,000 °C in scientific notation.
Step 1: Place a decimal to the right of the left-most digit.
2.0
Step 2: Count the number of places to the right of the decimal. There are 7, so the exponent of 10 would be
7.
107  10  10  10  10  10  10  10  10,000,000
Step 3: Write 20,000,000 in scientific notation.
20,000,000 °C  2.0  107 °C
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Using the example problem as a guide, answer the following questions. Remember to show your work.
1. The temperature of the core of the sun is about 15,000,000 °C. Use scientific notation to write the
temperature of the sun’s core.
2. The speed of light is approximately 300,000 km/s. Express this number using scientific notation.
3. The sun’s diameter is approximately 1,390,000 km. Use scientific notation to express the diameter of the
sun.
4. The sun converts more than 4,000,000 tons of matter to energy every second. Write 4,000,000 tons
using scientific notation.
5. Some gas jets that shoot out of the sun’s chromosphere reach 16,000 km in height. What is their height
in scientific notation?
Adapted from Holt McDougal Earth Science. Math Skills: Scientific Notation and the Sun. Austin, TX: Houghton Mifflin Harcourt Publishing Company, 2010. PDF.
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Evaluate
Review Questions
Answer the following questions.
1. Identify the 2 elements that make up most of the sun.
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2. Will the amount of hydrogen in the sun increase or decrease over the next few million years? Explain
your reasoning.
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3. What is the difference between the radiative zone and the convective zone of the sun?
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4. Explain why the sun’s corona can be seen during a solar eclipse but not at other times?
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5. How would a large geomagnetic storm affect communication on Earth?
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LESSON 5.3: STARS
Learning Goals for this Credit
Communicate scientific information clearly, thoroughly and accurately.
Use mathematics to represent physical variables and their relationships to make quantitative predictions and
to solve problems.
Learning Goals for this Lesson
 Describe how astronomers measure the composition, temperature, brightness, and distance of stars.
 Explain why stars appear to move in the sky.
 Describe the life cycle of a star.
Lesson Assignments
 Connect to Prior Knowledge
 Exploration Activity
 Reading and Questions
 Videos (optional)
 Starquakes Hold Secrets of Stellar Evolution
Engage
Connect to Prior Knowledge
Are you able to view any stars from where you live? What might affect the amount of stars you can see in the
sky?
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Explore
Exploration Activity
Astronomers can determine the temperature of individual stars based on their color. The surface temperature of
stars increases as you move across the spectrum from red to blue, as shown in the table below.
Star Color Versus Temperature
Surface Temperature (oC)
Less than 3,500
3,500 – 5,000
5,000 – 6,000
6,000 – 7,500
7,500 – 10,000
10,000 – 30,000
Above 30,000
Star Color
Red
Orange
Yellow
Yellow-white
White
Blue-white
Blue
This data can be plotted as a line graph to create a visual display, as shown in the line graph below. The x-axis
was chosen for star color to show the increase in surface temperature as you move across the spectrum from red
to blue. Temperature is on the y-axis. The low end of each temperature range was plotted on the graph. The
arbitrary value of 3000 °C was chosen for red.
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Use the line graph on the previous page to answer the following questions.
1. What is the low end of the range of surface temperatures for white stars?
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2. What is the low end of the range of surface temperatures for blue-white stars?
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3. What color of stars have a temperature of around 6,000 °C at the low end of their temperature range?
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4. What color of stars have a temperature of around 3,500 °C at the low end of their temperature range?
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Holt McDougal. Earth Science Chapter 30 Graphing Skills Worksheet. Austin, TX: Houghton Mifflin Harcourt Publishing Company, 2010. PDF.
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Explain
As you complete the reading, answer the questions in the space provided.
Reading
What Is a Star?
A star is a ball of very hot gases that emits, or gives off, light. This light comes from nuclear fusion within the
star. Nuclear fusion happens when small atomic nuclei combine to form larger atomic nuclei. Most stars in the
night sky appear to be tiny dots of white light. In fact, stars vary in color. For example, the star Antares shines
with a slightly reddish color. Our star, the sun, is a yellow star.
How Do Astronomers Learn About Stars?
Astronomers learn about stars by studying the light that stars emit. Astronomers study starlight with
spectrographs. Spectrographs are tools that separate light into different colors, or wavelengths. Light that
passes through a spectrograph produces a range of colors and lines called a spectrum. A star’s spectrum shows
the star’s composition and temperature. The flowchart below describes how a spectrum indicates a star’s
composition.
Elements in a star’s outer layers absorb different colors of light emitted by the star.
Therefore, the star produces a spectrum that does not contain all the colors of light.
⇩
Astronomers study a star’s spectrum to find out which colors of light the star’s
outer layers absorbed.
⇩
The colors missing from the star’s spectrum tell the astronomers what elements are
in the star.
Each chemical element absorbs and emits certain wavelengths of light. The colors and lines in the spectrum of a
star show which elements make up the star. Spectrum analysis shows that stars do not contain any elements that
are not found on Earth. The most common element in stars is hydrogen. Helium is the second most common
element in stars. Stars have small amounts of other elements, such as carbon, oxygen, and nitrogen. The color
of a star indicates the star’s temperature. Most star temperatures range from 2,800 oC to 24,000 oC. Blue stars
are the hottest. Their average surface temperature is 35,000 oC. Red stars are the coolest. Their average surface
temperature is 3,000 oC. Yellow stars have surface temperatures of about 5,500 ̊C. The table on page 26 shows
the relationship between star color and temperature. Stars vary in size. The smallest stars are slightly bigger
than Jupiter. These stars are about one-seventh the size of our sun. Most of the stars you see in the sky are about
the size of our sun. The sun is a medium-sized star. It has a diameter of about 1,390,000 km. Some giant stars
have diameters that are 1,000 times the sun’s diameter. Stars also vary in mass. Many stars have about the same
mass as the sun. However, some stars have higher or lower masses than the sun. Very dense stars may have
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more mass than the sun and still be smaller than the sun. Less dense stars may be larger than the sun but have
less mass than the sun.
1. How do scientists determine the temperature of a star? Give one example to support your answer.
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How Do Stars Move in the Sky?
Two kinds of motion are associated with stars: apparent motion across the night sky and actual motion through
space. The apparent motion of stars is easy to see. Astronomers must use telescopes and spacecraft to study the
actual motion of stars. From Earth, stars appear to move across the night sky. This apparent motion of stars
results from the movement of Earth. As Earth rotates, stars seem to move in a circle around a central star. This
central star is called Polaris, or the North Star. Polaris does not seem to move much because it is directly over
the North Pole. Earth’s revolution around the sun also causes apparent motion. As Earth orbits the sun, different
stars become visible during different seasons. The visible stars seem to move slightly to the west each night.
After many months, some stars disappear below the western horizon. Some stars are always visible in the night
sky. These stars never pass below the horizon. These stars are called circumpolar stars. The stars of the Little
Dipper are circumpolar for most people in the Northern Hemisphere. At the North Pole, all visible stars are
circumpolar. As you move away from the North Pole toward the equator, you can see fewer circumpolar stars.
Most stars have several types of actual motion. First, they move through the universe. This motion is not
related to Earth’s rotation or revolution. Second, they may revolve around another star. Third, they either move
away from or toward our solar system. Astronomers study a star’s spectrum to learn about the star’s motion
toward or away from Earth. As a star moves, its spectrum seems to shift, or change. This shift in the spectrum is
called the Doppler effect. The Doppler effect happens when an observer and a light source move toward or
away from each other. For example, light from stars moving toward Earth shifts toward blue. This shift is
called blue shift. The wavelengths of light appear to be shorter as the star moves toward Earth. Light from stars
moving away from Earth shifts toward red. This shift is called red shift. The wavelengths of light appear to be
longer. This can be seen in the diagram below.
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2. Why do stars appear in different parts of the sky during different months?
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3. What is a circumpolar star?
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How Do Astronomers Describe Distances?
Objects in space are very far apart. For this reason, astronomers describe distances in space using light-years. A
light-year is the distance that light travels in one year. Light travels about 9.46 trillion km in one year. Light
from stars takes time to reach Earth. As a result, we see light that left stars sometime in the past. For instance,
light from the sun takes about 8 minutes to reach Earth. The light leaves the sun 8 minutes before we see it.
Polaris is about 430 light-years from Earth. Therefore, when you look at Polaris, you see the star the way it was
430 years ago. Scientists can use parallax to determine the distance to stars that are relatively close to Earth.
Parallax is the apparent shift in a star’s position when it is viewed from different places. Observers can study
stars from different places as Earth orbits the sun. As Earth orbits, a nearby star will appear to move compared
to stars that are farther from Earth. The closer the star is to Earth, the larger the shift will be.
How Do Astronomers Describe Brightness?
About 6,000 stars are visible from Earth without a telescope. With a telescope, about 3 billion stars are visible.
Billions more stars are visible from telescopes that orbit the Earth, such as the Hubble Space Telescope. The
visibility of a star depends on its brightness and distance from Earth. Astronomers use two scales to describe the
brightness of a star. The brightness of a star as seen from Earth is called the star’s apparent magnitude. The
apparent magnitude of a star depends on how much light the star emits. It also depends on how far the star is
from Earth. The brighter the star appears from Earth, the lower the number of its apparent magnitude.
Astronomers also measure the true brightness, or absolute magnitude, of stars. The absolute magnitude is how
bright a star would appear if all stars were the same distance from Earth. The brighter a star is, the lower the
number of its absolute magnitude.
How Do Scientists Study and Classify Stars?
A typical star exists for billions of years. For this reason, astronomers cannot observe one star for its entire
lifetime. Instead, astronomers study stars in different stages of development. Astronomers use this information
to learn how stars change over time. To classify stars, scientists measure temperature and luminosity.
Luminosity is the total amount of energy that a star gives off each second. Scientists have found a relationship
between temperature and luminosity. The graph that shows this relationship is the Hertzsprung-Russell
diagram, or H-R diagram. Astronomers plot the highest temperatures on the left. They plot the highest
luminosities at the top. The temperature and luminosity of most stars fall in a diagonal band on the graph. This
band is called the main sequence. Stars in this band are called main-sequence stars or dwarfs. The sun is a
main-sequence star.
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4. Where do most stars fall on the Hertzsprung-Russel diagram?
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How Do Stars Form?
A star begins in a nebula. A nebula is a cloud of gas and dust. Most nebulas contain 70% hydrogen, 28%
helium, and 2% heavier elements. An outside force, such as the explosion of a nearby star, may cause the
nebula to start to collapse. The nebula may also start to collapse without a known force. Nebulas follow
Newton’s law of universal gravitation. This law states that all objects in the universe attract each other. This
force of attraction increases as the mass of an object increases. The force also increases when objects get closer
together. Therefore, the attraction between the particles in a nebula increases as gravity pulls them closer
together. The increased force of attraction pulls in more nearby particles. The mass continues to increase. As
more particles come together, dense regions of matter build up in the nebula. Over time, nebulas may form
protostars. This process has many stages, as described below.
i.
ii.
iii.
iv.
Gravity causes dense regions in the nebula to contract. As a result, any spin in the region increases.
The shrinking, spinning region flattens into a disk called a protostar. Matter collects in the center of the
protostar.
As more matter enters the protostar, gravitational energy changes to heat. This heat energy increases the
temperature of the protostar.
The protostar continues to contract and increase in temperature for millions of years.
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v.
Over time, the gas in the protostar becomes extremely hot. As a result, electrons in the gas separate from
their parent atoms.
The nuclei and free electrons move independently. The gas becomes a plasma. Plasma is a hot gas that
is made up of electrically charged particles. It has an equal number of positive ions and electrons.
vi.
Temperature continues to increase in a protostar to about 10,000,000 ̊C. At this temperature, nuclear fusion
begins. High temperature and pressure cause small atomic nuclei to combine into larger nuclei. Nuclear fusion
releases large amounts of energy. The start of fusion marks the birth of a star. Nuclear fusion can continue for
billions of years. Fusion happens faster as gravity increases the pressure on the matter in the star. At the same
time, the energy from fusion heats the gas in the star. The energy and hot gas push outward and resist the
inward pull of gravity. These forces balance each other. This balance makes the star stable in size.
5. What is the main force that causes a protostar to become a star?
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What Is the Main-Sequence Stage?
The longest stage in the life of a star is the main-sequence stage. During this stage, nuclear fusion continues in
the core of the star. Hydrogen fuses into helium and produces energy. A star with the same mass as the sun
stays on the main sequence for about 10 billion years. Stars with more mass fuse hydrogen more quickly. They
may stay on the main sequence for only 10 million years. However, less massive stars can stay on the main
sequence for hundreds of billions of years. Our sun has fused about 5% of its hydrogen over a period of 5
billion years. After another 5 billion years, the rate of fusion in the core will decrease. The sun’s temperature
and luminosity will change. At that time, the sun will leave the main sequence.
How Do Stars Leave the Main Sequence?
Eventually, stars leave the main sequence. This process starts when about 20% of the hydrogen atoms in a star’s
core have fused into helium atoms. This process has several stages:
i.
ii.
iii.
iv.
v.
Gravity causes the core of the star to contract.
The contraction heats the core. The helium core transfers energy to a shell of hydrogen around the core.
The energy causes hydrogen fusion to continue in the outer layers of the star.
The hydrogen fusion radiates large amounts of energy outward.
The radiation causes the outer shell of the star to expand.
A star’s shell of gases cools as it expands. As the gases get cooler, their glow becomes reddish. The star
becomes larger and redder. These large, red stars are called giants. They are bigger than main-sequence stars of
the same surface temperature. Giant stars have large surface areas. For this reason, they are very bright. Giants
can be more than 10 times larger than the sun. Over time, stars with the same mass as the sun will become
giants. As these stars become larger and cooler, they move off the main sequence. Massive stars become larger
than giants as they leave the main sequence. These very luminous stars are called supergiants. Supergiants can
be more than 100 times larger than the sun. The supergiant Betelgeuse is 1,000 times larger than the sun.
Supergiants are easy to find in the night sky because they are so bright. However, their surfaces are cool
compared to the surfaces of other stars.
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6. Over time, how does the amount of hydrogen in a star change? Explain your answer.
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What Are the Final Stages of a Sun-like Star?
The final stages in a star’s life cycle depend on the size of the star. Stars about the size of the sun follow a
similar cycle. Fusion in the core stops when helium atoms have fused into carbon and oxygen. The supply of
energy from fusion drops, and the star enters its final stages. In its final stages, a star’s outer gases drift away.
The remaining core heats these gases. The gases appear as a planetary nebula. A planetary nebula is a cloud of
gas that forms around a dying star. These clouds may form different shapes around the star, such as a sphere or
ring.
Over time, the gases in a planetary nebula drift away. Gravity pulls the remaining matter in the star inward. The
matter moves inward until it cannot contract any more. A hot, dense core of matter called a white dwarf
remains. White dwarfs shine for billions of years before they cool completely. White dwarfs are hot but dim. As
white dwarfs cool, they lose brightness. This is the final stage in the life cycle of many stars. Some white dwarf
stars are part of binary star systems. A binary star system involves two stars. For example, a white dwarf may
revolve around a red giant. The gravity of the white dwarf may pull gases from the red giant. These gases
collect on the surface of the white dwarf and build up pressure. This pressure may cause large explosions, which
release energy and matter into space. This release of energy is called a nova. A nova may cause a star to
become much brighter than it normally is. However, the nova starts to fade after a few days. Novas do not
usually destroy the binary star system. Thus, a white dwarf may become a nova many times. A white dwarf in a
binary system may also become a supernova. A supernova is a star that explodes and blows itself apart. The
steps below describe how a supernova forms.
i.
ii.
iii.
A white dwarf collects mass on its surface from a nearby red giant.
The gravity pulling on the mass overpowers the outward pressure.
The star collapses. It becomes so dense that the outer layers explode outward.
Supernovas are much more violent than novas. The explosion of a supernova destroys the white dwarf star. It
may also destroy much of the red giant.
What Are the Final Stages of Massive Stars?
Some stars have masses more than 8 times the mass of the sun. The final stages of these massive stars are
different from the final stages of less-massive stars.
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Only a small percentage of white dwarfs become supernovas. However, massive stars become supernovas as
part of their life cycle. After the supergiant stage, these stars contract very quickly. The collapse of a massive
star creates very high pressures and temperatures. Nuclear fusion begins again. This time, carbon atoms fuse
into heavier elements, such as oxygen, magnesium, or silicon. Fusion continues until the core is made of iron.
Iron has a very stable nuclear structure. Therefore, fusion of iron takes energy from the star instead of releasing
energy. The star loses its supply of fuel, and the core begins to collapse. The collapse releases energy. This
energy moves to the outer layers of the star. The outer layers explode outward with great force in a supernova.
Massive stars do not become white dwarfs. After a supernova, the core may become a small, dense ball of
neutrons called a neutron star. Neutron stars spin very quickly. Some neutron stars emit a beam of radio
waves. These neutron stars are called pulsars. A pulsar rotates, or spins. As it spins, its beam sweeps across
space. Scientists can detect the beam every time it sweeps past Earth. The star rotates between each pulse they
detect. Newly formed pulsars often have the remains of a supernova around them. However, most known
pulsars are very old. The supernova remains have gone away. Only the spinning star is left. After a supernova,
some massive stars leave a core that is more than 3 times the sun’s mass. In this case, the star may contract
more because of gravity. This force crushes the dense core and leaves a black hole. The gravitational pull of a
black hole is very strong. Not even light can escape it. Black holes are hard to find because they do not emit
light. However, black holes have effects on nearby stars. The black hole pulls matter from the star. The matter
swirls around the black hole before being absorbed. The matter becomes very hot and releases X rays.
Astronomers can detect these X rays. Then, astronomers try to find the object affecting the star. The star’s
motion may show that a massive, invisible object is nearby. Astronomers conclude that the object is a black
hole.
7. How can scientists detect a black hole if it does not emit light?
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Allison, Mead A., et al. “Chapter 30: Stars, Galaxies, and the Universe/Section 1: Characteristics of Stars.” Holt McDougal Earth Science Interactive Reader, Holt
McDougal, a Division of Houghton Mifflin Harcourt Publishing Co., 2010, pp. 467-472.
Allison, Mead A., et al. “Chapter 30: Stars, Galaxies, and the Universe/Section 2: Stellar Evolution.” Holt McDougal Earth Science Interactive Reader, Holt McDougal,
a Division of Houghton Mifflin Harcourt Publishing Co., 2010, pp. 473-480.
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Videos
If you would like to learn more about this topic, watch the videos below for more information. (Optional)
The Life Cycle of Stars (4:58)

“The Life Cycle of Stars.” YouTube. Institute of Physics, 1 Nov. 2012. Web. 02 July 2015.
How is a star born, and how does it die? This video will explain the life cycle of a star
and show how the different elements found throughout the universe are created.
How Do We Measure the Distance of Stars? (9:51)

“How Do We Measure the Distance of Stars?” YouTube. SciShow, 8 Sept. 2014. Web. 02 July 2015.
How do astronomers know how far away stars and other objects in the universe are from
us on Earth? In this video you will see what techniques are used to measure distances to
objects outside of our solar system, and even objects outside of our galaxy.
What Are Stars Made Of? | Real Talk With A Scientist (4:37)

“What Are Stars Made Of? | Real Talk With A Scientist.” YouTube. DNews, 28 Feb. 2015. Web. 02 July 2015.
How do scientists determine what stars are made of? This video will discuss how
spectroscopy is used to give a stars elemental “finger print”.
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Elaborate
Starquakes Hold Secrets of Stellar Evolution
A NASA spacecraft designed to seek out alien worlds has also revealed new details about the structure and
evolution of stars, and should help astronomers better understand the future of our own sun, researchers
announced. Researchers measured so-called “starquakes,” observing oscillations in the brightness of thousands
of stars in much the same way geologists study earthquakes to probe our planet’s interior. NASA’s planethunting Kepler spacecraft served as their tool. The method, called asteroseismology, is helping astronomers
characterize stars as never before, researchers said during a news conference at Aarhus University in Denmark.
“We are just about to enter a new area in stellar astrophysics,” Thomas Kallinger, of the University of British
Columbia and the University of Vienna, said in a statement. “Kepler provides us with data of such good quality
that they will change our view of how stars work in detail.”
Kepler: A Multipurpose Instrument
NASA launched the Kepler spacecraft in March 2009 with a primary mission of finding Earth-like alien planets.
So far, it has identified at least 700 “candidate stars” that could harbor alien worlds. But researchers are also
using the spacecraft to analyze the stars such planets may be circling. “Our knowledge of the planets Kepler
discovers is only as good as our knowledge of the stars that they orbit,” said Kepler mission co-investigator
Natalie Batalha, of San Jose State, during the news conference. As an example of what asteroseismology can
reveal, the researchers offered up a star called KIC 11026764. By studying its pulses, astronomers have learned
more about this star than they know about virtually any star in the universe aside from our sun. Researchers
determined, for example, that KIC 11026764 is 5.94 billion years old and is roughly twice the size of our sun.
KIC 11026764 will continue to grow, eventually transforming into a red giant, researchers said. Such
information, once gathered for hundreds or thousands of stars, will help astronomers understand stellar structure
and evolution in a general sense. And it could help scientists evaluate the chances that alien planets could
harbor life, researchers said. Kepler detects alien planets by watching for the telltale dimming in a star’s
brightness caused when a planet crosses in front of it from Kepler’s vantage point. The amount of dimming
reveals how big the planet is relative to its star — but not its actual size. So knowing the size of the star will tell
researchers how big its planets are, if it has any, researchers said. Knowing a star’s age and what stage it is at in
its stellar evolution can also help astronomers judge how likely it is for any alien planets around it to harbor life.
No planets are known to orbit KIC 11026764, but asteroseismology could theoretically be applied to stars that
host planets, researchers said.
Red Giants and Stellar Lighthouses, Too
Astronomers have been using Kepler to characterize the structure and life cycle of 1,000 red giants. Later in its
life, the sun will one day become one of these huge, bloated stars. Researchers also reported on the star RR
Lyrae. It has been studied for more than 100 years as the first member of an important class of stars used to
measure cosmological distances. The brightness of the star oscillates within a well-known period of about 13.5
hours, researchers said. Yet during that period, other small, cyclic changes in amplitude occur — behavior
known as the Blazhko effect. The effect has puzzled astronomers for decades, but Kepler data may have
yielded a clue to its origin, researchers said. Kepler observations revealed an additional oscillation period that
had never been previously detected. The oscillation occurs with a time scale twice as long as the 13.5-hour
period. The Kepler data indicates the doubling is linked to the Blazhko effect. “Kepler data ultimately will give
us a better understanding of the future of our sun and the evolution of our galaxy as a whole,” Daniel Huber, of
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the University of Sydney, said in a statement. The Kepler spacecraft uses a huge digital camera, known as a
photometer, to continuously monitor the brightness of more than 150,000 stars in its field of view as it orbits
the sun. The research team using the telescope to study stars is an international collaboration known as the
Kepler Asteroseismic Science Consortium.
Wall, Mike. “Starquakes Hold Secrets of Stellar Evolution.” LiveScience. TechMedia Network, 26 Oct. 2010. Web. 16 Jan. 2016. .
Evaluate
Answer the following questions using the article above.
1. What are “starquakes”?
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2. When NASA launched the Kepler spacecraft in 2009, what was its primary mission?
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3. How large is KIC 11026764 compared to the sun?
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4. How does the Kepler spacecraft detect planets?
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5. What is the next step in the sun’s lifecycle?
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6. What type of camera does the Kepler spacecraft use to monitor the brightness (magnitude) of stars?
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LESSON 5.4: THE UNIVERSE
Learning Goals for this Credit
Communicate scientific information clearly, thoroughly and accurately.
Use mathematics to represent physical variables and their relationships to make quantitative predictions and
to solve problems.
Learning Goals for this Lesson
 Describe the characteristics that make up a constellation.
 Describe the three main types of galaxies.
 Explain how Hubble’s discoveries led to an understanding that the universe is expanding.
 List evidence for the Big Bang Theory.
Lesson Assignments
 Connect to Prior Knowledge
 Exploration Activity
 Reading and Questions
 Videos (optional)
 Stars, Galaxies, and the Universe Concept Map
 Review Questions
Engage
Connect to Prior Knowledge
Besides stars and planets, what other astronomical objects can be found in the universe?
__________________________________________________________________________________________
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Explore
Exploration
Activity
Until recently, astronomers
thought they knew about all the
star groups in our galaxy, the
Milky Way. However, infrared
images from NASA’s Spitzer
Space Telescope and the
University of Wyoming Infrared
Observatory revealed a new,
globular cluster in the Milky Way.
The globular cluster is one of
about 150 that orbit the center of
the Milky Way. The cluster was
first spotted on a survey of infrared
radiation designed to find objects
hidden in the dusty mid-plane of
the Milky Way. Infrared radiation
can be detected from anything that
gives off heat. It has a range of
wavelengths; just as visible light
does. Even though dust blocks
visible light from much of the
Milky Way, infrared telescopes
can “see” things where there is no
light.
1. If objects cannot be seen
from Earth with optical telescopes, how are astronomers able to study them?
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2. Explain how the new, globular cluster was spotted.
_______________________________________________________________________________________
_______________________________________________________________________________________
3. Compare observations using infrared radiation and observations that rely on visible light.
_______________________________________________________________________________________
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Allison, Mead A., et al. “Chapter 30: Stars, Galaxies, and the Universe/Critical Thinking Worksheet.” Holt McDougal Earth Science, Holt McDougal, a Division of
Houghton Mifflin Harcourt Publishing Co., 2010.
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Explain
As you complete the reading, answer the questions in the space provided.
Reading
What Are Constellations?
You can see many individual stars on a clear night. These visible stars are only some of the stars in the universe.
Most of the stars we see are within 100 light-years of Earth. Astronomers organize individual stars into
patterns. These patterns of stars and the space around them are called constellations. The stars in a constellation
appear to be close together. However, these stars are not all the same distance from Earth. In fact, they may be
very distant from each other. Stars appear to stay fixed in their patterns. The positions of the stars in relation to
each other do not seem to change over weeks and months. This is because we view the stars from a great
distance. In 1930, astronomers around the world agreed on a standard set of 88 constellations. These
constellations divide the sky into regions. You can use a map of the constellations to find a specific star.
1. Why do the stars in a constellation not seem to change position over time?
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What Are Multiple-Star Systems?
Stars are not always isolated, or alone. Two or more stars may form multiple-star systems. More than half of all
sun-like stars are part of multiple-star systems. Binary stars are pairs of stars that revolve around each other.
Gravity holds the pairs of stars together. A binary star has a center of mass, or barycenter. The stars orbit
around the barycenter. When the two stars have similar masses, the barycenter is somewhere between the stars.
If one star is more massive, the barycenter is closer to the more massive star. Multiple-star systems can have
more than two stars. For instance, two stars may revolve quickly around a common barycenter. A third star
may revolve around the same barycenter slowly, farther away from the two stars.
What Is a Star Cluster?
Sometimes, nebulas collapse to form groups of stars called clusters. Clusters can have hundreds or thousands
of stars. The table below describes two types of clusters.
Type of Cluster
Shape
Number of Stars
Globular Cluster
Sphere
up to 1,000,000 stars
Open Cluster
Loosely Shaped
A Few Hundred Stars
What Is a Galaxy?
The universe has hundreds of billions of galaxies. A galaxy is a large group of stars, gas, and dust held together
by gravity. Galaxies are the major building blocks of the universe. A typical galaxy has a diameter of about
100,000 light-years. It may contain more than 200 billion stars. Astronomers can use stars to find distances to
galaxies. For instance, astronomers can study giant stars called Cepheid variables. These stars brighten and
fade in a regular cycle. Most Cepheid variables have cycles that range from 1 to 100 days. The longer the cycle,
the brighter the star’s absolute magnitude is. Astronomers can compare a Cepheid variable’s absolute
magnitude and apparent magnitude to find the distance to the star. This distance tells astronomers the distance
to the galaxy where the star is. Astronomers classify galaxies by shape. The most common type of galaxy is a
spiral galaxy. Some spiral galaxies have a straight bar of stars through the center. These galaxies are called
barred spiral galaxies. The other two types of galaxies are elliptical galaxies and irregular galaxies. Irregular
galaxies make up a small percentage of the total known galaxies. The table below describes the three types of
galaxies.
Types of Galaxy
Spiral Galaxy
Elliptical Galaxy
Irregular Galaxy
Shape
Description
Flat arms that spiral around a
center of bright stars
A sphere of oval with a bright
center
Billions of young stars, gas and
dust
A few young stars; not much gas
and dust
Low total mass; large amounts of
gas and dust
No particular shape
Sometimes, a cloudlike band is visible across the night sky. This band is called the Milky Way. We see this
band of stars when we look through our own galaxy. The Milky Way galaxy is a spiral galaxy. The sun is one
of billions of stars in this galaxy. Each star orbits around the center of the galaxy. The sun takes about 225
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million years to complete one orbit around the galaxy’s center. About 30 other galaxies are within 5 million
light-years of the Milky Way. These galaxies and the Milky Way galaxy make up the Local Group.
2. How can astronomers use Cepheid variables to figure out how far away a galaxy is?
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3. What are the three main types of galaxies?
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What Are Quasars?
The word quasar is a shortened term for quasi-stellar radio source. Through a telescope, a quasar looks like a
small, faint star. However, quasars are not related to stars. They are related to galaxies. Quasars appear in some
very distant galaxies. Galaxies with quasars in them have very bright centers. Some quasars emit a stream of
gas. The large amount of energy a quasar emits may be produced by a giant black hole. The mass of this black
hole may be billions of times the mass of our sun.
4. How is a galaxy with a quasar in it different from other galaxies?
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_______________________________________________________________________________________
_______________________________________________________________________________________
What Is Cosmology?
The study of the origin, structure, and future of the universe is called cosmology. Scientists who study
cosmology are cosmologists. Cosmologists study the universe as a whole. Astronomers study the parts of the
universe, such as planets, stars, and galaxies. Cosmologists have theories about how the universe began and
how it is changing. They test these theories against new observations. Many of these theories began with
observations made less than 100 years ago.
How Do We Know That Galaxies Move?
Scientists use light to study the movement of objects in space. As an object moves, its light seems to shift on
the spectrum toward red or blue, as shown below.


Blue shift = object moving toward Earth
Red shift = object moving away from Earth
In the early 1900s, the astronomer Edwin Hubble studied spectra from galaxies. His research uncovered new
information about the universe. In the 1920s, Hubble found that the spectra of distant galaxies are all red42
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shifted. Hubble used this red shift to determine how fast the galaxies are moving away from Earth. Hubble
found that the most distant galaxies show the greatest red shift. Thus, these distant galaxies are moving away
from Earth the fastest. Modern telescopes with cameras can take images of spectra. These spectra all confirm
Hubble’s original observations. Imagine a raisin cake rising in an oven. If you could sit on one raisin, you
would see the other raisins moving away from you. Raisins that are farther away would move away faster. This
is because more cake is between you and these distant raisins, and the whole cake is expanding. The situation is
similar with galaxies and the universe.
5. Describe Edwin Hubble’s observations and explain how they show that the universe is expanding.
_______________________________________________________________________________________
_______________________________________________________________________________________
_______________________________________________________________________________________
What Is the Big Bang Theory?
Cosmologists have offered different theories to explain why the universe is expanding. The current and most
accepted theory is the Big Bang Theory. This theory states that all matter and energy in the universe was once
compressed into a very small space. About 14 billion years ago, a sudden event called the big bang happened.
The big bang sent all of the matter and energy outward in all directions. As a result, the universe expanded.
Some of the matter came together in clumps, which evolved into galaxies. Today, the universe is still
expanding. The galaxies continue to move apart from each other. This expansion explains the red shift of distant
galaxies. A discovery made in the 1960s supports the big bang theory. In 1965, scientists detected cosmic
background radiation, or low levels of energy, from all directions in space. Astronomers think that this
background radiation formed just after the big bang. The universe has cooled since the big bang. The energy of
background radiation has a temperature of about –270 o C. This temperature is only three o C above absolute
zero, which is the lowest temperature possible. Satellite maps of cosmic background radiation show “ripples”
in temperature. These ripples show that cosmic background radiation is uneven in some places. This is because
matter was not spread evenly in the early universe. The ripples show the early stages of the universe’s first
galaxies.
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6. How does the Big Bang Theory explain the existence of cosmic background radiation?
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_______________________________________________________________________________________
_______________________________________________________________________________________
What Materials Make Up the Universe?
Astronomers are continuing to research ripples in cosmic background radiation. They are also studying
distances to supernovas in ancient galaxies. This research has helped astronomers learn more about the structure
of the universe. Astronomers now think that the universe is made of more mass and energy than they can detect.
The ripples in cosmic background radiation show that the universe may contain different types of matter.
Regular, visible matter makes up only 4% of the universe. Another 23% of the universe is made of dark
matter. Dark matter does not emit or reflect light, but scientists can detect its gravity. Research also shows that
most of the universe is made of an unknown material called dark energy. Dark energy acts as a force against
gravity. Scientists think that some form of dark energy is pushing galaxies apart. Dark energy is causing the
universe to expand faster and faster.
7. How do scientists detect dark matter?
_______________________________________________________________________________________
_______________________________________________________________________________________
_______________________________________________________________________________________
Allison, Mead A., et al. “Chapter 30: Stars, Galaxies, and the Universe/Section 3: Star Groups.” Holt McDougal Earth Science Interactive Reader, Holt McDougal, a
Division of Houghton Mifflin Harcourt Publishing Co., 2010, pp. 481-484.
Allison, Mead A., et al. “Chapter 30: Stars, Galaxies, and the Universe/Section 4: The Big Bang Theory.” Holt McDougal Earth Science Interactive Reader, Holt
McDougal, a Division of Houghton Mifflin Harcourt Publishing Co., 2010, pp. 485-488.
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Videos
If you would like to learn more about this topic, watch the videos below for more information. (Optional)
Constellations: Connect the Dots in the Sky! (3:44)

“Constellations: Connect the Dots in the Sky!” YouTube. SciShow Kids, 30 Apr. 2015. Web. 07 July 2015.
What constellations are easiest to see and how do you spot them? This video will
discuss how to find a few of the more easily visible constellations in the night sky.
Cycles in the Sky: Crash Course Astronomy (9:29)
https://www.youtube.com/watch?v=01QWCrZcfE&list=PL8dPuuaLjXtPAJr1ysd5yGIyiSFuh0mIL&index=3
“Cycles in the Sky: Crash Course Astronomy #3.” YouTube. CrashCourse, 29 Jan. 2015. Web. 07 July 2015.
Why do the constellations in the sky move in a cycle? Why can’t you find the
same constellations in the sky during different seasons? This video will discuss the
cycles that we are able to observe in the universe.
The Big Bang: Crash Course Big History #1 (14:24)

“The Big Bang: Crash Course Big History #1.” YouTube. CrashCourse, 17 Sept. 2014. Web. 08 July 2015.
What is the Big Bang Theory? What evidence do scientists have that the big bang
occurred around 14 billion years ago? This video will explain what occurred
during the big bang, and how we can still observe it.
Dark matter: The matter we can’t see – James Gillies (5:34)

“Dark Matter: The Matter We Can’t See – James Gillies.” YouTube. Ted-Ed, 3 May 2013. Web. 09 July 2015.
What exactly is dark matter and how do we know it exists? This video will explain
the mystery behind dark matter and what scientists currently know about it.
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Elaborate
Stars, Galaxies, and the Universe Concept Map
Complete the concept map below to show the relationship between stars and galaxies using the following terms.
Each term can be found in the reading from lessons 5.3 and 5.4.
Irregular Galaxies
Main Sequence
Spiral Galaxies
Galaxies
Elliptical Galaxies
Protostars
Neutron Stars
Supergiants
Stars
Black Holes
Giants
Allison, Mead A., et al. “Chapter 30: Stars, Galaxies, and the Universe/Concept Map: Stars, Galaxies, and the Universe.” Holt McDougal Earth Science, Holt
McDougal, a Division of Houghton Mifflin Harcourt Publishing Co., 2010.
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Evaluate
Review Questions
Answer the following questions.
1. Which type of galaxy is our Milky Way Galaxy?
_______________________________________________________________________________________
_______________________________________________________________________________________
_______________________________________________________________________________________
2. Why are constellations seen in the winter sky different from those seen in the summer sky?
_______________________________________________________________________________________
_______________________________________________________________________________________
_______________________________________________________________________________________
3. Describe how red shifts were used by cosmologists to determine that the universe was expanding. How
is this evidence for the big bang theory?
_______________________________________________________________________________________
_______________________________________________________________________________________
_______________________________________________________________________________________
Revisit the essential question. Did your answer change? Why or why not?
Essential Question
Do you think that the universe has a starting point and ending point? Explain your answer.
__________________________________________________________________________________________
__________________________________________________________________________________________
__________________________________________________________________________________________
__________________________________________________________________________________________
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Learning Goals for this Credit
Communicate scientific information clearly, thoroughly and accurately.
Use mathematics to represent physical variables and their relationships to make quantitative predictions and to solve problems.
Lesson
5.1
Title
Observing Space
5.2
The Sun
5.3
Stars
5.4
The Universe
Learning Goals For Each Lesson

Describe characteristics of the universe in terms of time, distance, and organization.

Identify the visible and nonvisible parts of the electromagnetic spectrum.

Calculate distances in light-years.

Explain how the sun converts matter into energy in its core.

Describe the layers of the sun’s interior and atmosphere.

Use scientific notation to express large numbers.

Describe how astronomers measure the composition, temperature, brightness, and distance of stars.

Explain why stars appear to move in the sky.

Describe the life cycle of a star.

Describe the characteristics that make up a constellation.

Describe the three main types of galaxies.

Explain how Hubble’s discoveries led to an understanding that the universe is expanding.

List evidence for the big bang theory.
General Science Rubric
Credit Grading
Responses to Packet
and Questions
40 pts.
Performance Task
40 pts.
Quiz
20 pts.
4
 My responses in
my packet show
clear reasoning and
use of evidence.
3
 My responses in
my packet show
basic reasoning and
use of evidence.
2
 My responses in
my packet show
basic reasoning but
limited evidence to
support it.
1
 My answers to the
questions in my
packet are either
unscientific or
overly simplistic,
and have limited
evidence.
 I completed some
of the expectations
of the assignment
to show what I
know.
 I completed some
of the expectations
but struggled to
show what I know.
 I made connections
to other ideas
within and across
science credits.
 I completed all of
the expectations of
the assignment to
thoroughly show
what I know.
 My explanation is
clear and supported
by valid scientific
evidence.
 I mainly completed
the expectations of
the assignment to
show what I know.
 My explanation is
supported by
scientific evidence.
 My explanation is
simplistic or basic
and supported by
limited scientific
evidence.
 My explanation is
not supported by
scientific evidence.
Students receive 2 points per correct response.
___x 10 = ___/40
___x 10 = ___/40
___x2 = ___/20
Total:
___/100
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