Download Lesson 1 The Sun and Other Stars

Lesson 1
The Sun and
Other Stars
On January 20, 2005, satellites that carried
cell phone and cable signals suddenly shut
down. They had been struck by a burst of
energy. Where did this energy come from?
410
ENGAGE
ESS.39 Identify the physical characteristics of the Sun (ESS-M-C1) ESS.40 Describe the
significance of Polaris as the North Star (ESS-M-C1)
How do the sizes of Earth
and the Sun compare?
Materials
Purpose
Study the size difference between Earth and the Sun.
Procedure
Use Numbers What proportion is the size of Earth
to the size of the Sun?
Use Numbers What would the diameter of the Sun
• meter stick
be if the diameter of Earth was 0.5 cm?
• ruler
Make a Model Use appropriate tools to design
• colored pencils
a model of Earth and the Sun to this scale.
How many Earths would it take to cover the length
of the model of the Sun’s diameter?
Draw Conclusions
• clear tape
Step
Diameter
The Sun
1,390,000 kilometers
Communicate Does this model show an accurate
Earth
12,760 kilometers
comparison between the diameters of the Sun and
Earth? Why or why not?
Step
Explore More
How does the Sun’s diameter compare with
that of Jupiter, the largest planet? Do research
to answer this question and make a model to
represent the difference in their sizes.
SI.14 Develop models to illustrate or explain conclusions
reached through investigation (SI-M-A5) SI.15 Identify
a
and explain the limitations of models used to represent
tthe natural world (SI-M-A5)
Also covers SI.3
411
EXPLORE
▶ Essential Question
What are the characteristics
of the Sun and other stars?
ESS.39, ESS.40
▶ Vocabulary
star, p. 413
astronomical unit, p. 413
solar flares, p. 415
constellation, p. 416
▶ Reading Skill
Sun
Draw Conclusions
Text Clues
Conclusions
▶ Technology
e-Glossary and e-Review online
at www.macmillanmh.com
Earth
Earth and the Sun are shown here on a scale
of 1 centimeter = 50,000 kilometers. At this
size, Earth and the Sun are 2,992 cm (about
98 feet) apart.
412
EXPLAIN
What is the Sun?
Finding the Sun’s Mass
The Sun is a star. A star is an
object that produces thermal and
light energy. The Sun is at the center
of the solar system. The solar system
includes all the planets and other
objects that orbit the Sun.
It is impossible to measure the
weight of the Sun. After all, the Sun
cannot be put on a scale.
The stars that produce the most
energy make about 10 million times
more energy than the Sun. The
least-productive stars make only
one-hundredth as much energy as
the Sun.
The Sun is an average-sized star
and the largest object in the solar
system. The Sun’s diameter is about
1,390,000 kilometers (863,706 miles).
If the Sun were a hollow ball, more
than 1 million Earths could fit inside
it. The Sun looks larger than the other
stars that can be seen in the night sky
because it is much closer to Earth.
The mean, or average, distance
between the Sun and Earth is
149,591,000 km (92,960,000 mi).
To scientists, this distance is
known as one astronomical unit
(as•truh•NAH•mi•kulh), or AU. The nextclosest stars are found in the Alpha
Centauri star system. They are about
271,931 AUs away.
However, it is possible to measure
the mass of the Sun. Recall that mass
is the amount of matter in an object.
The mass of the Sun can be calculated
if you know two facts. The first fact
is the length of time it takes for a
planet to make one trip around the Sun
(for Earth, that is 365.24 days). The
second fact is the distance between the
planet and the Sun (for Earth, that is
149,591,000 km).
Using this information, scientists
have calculated the Sun’s mass to be
2 million trillion trillion kilograms.
That’s 2,000,000,000,000,000,000,
000,000,000,000 kg! This is 745 times
greater than the mass of all the other
objects in the solar system put together.
As a matter of fact, the mass of the Sun
makes up 99.8 percent of all the mass
in the solar system.
Quick Check
Draw Conclusions Why are the
planets not stars?
Critical Thinking Why are
astronomical units used to measure
distances rather than kilometers?
413
EXPLAIN
What are the parts
of the Sun?
The Sun is a huge sphere made up
mostly of two very light gases, hydrogen
and helium. Hydrogen makes up about
71 percent of the Sun’s mass. Another
27 percent is made up of helium.
Oxygen, carbon, and other gases make
up the remaining 2 percent of the Sun’s
mass.
Most of the energy that the Sun
produces is formed in its core. At its
core, the Sun has a temperature of
10 million to 20 million degrees
Celsius (18 million to 36 million
degrees Fahrenheit). The pressure is
more than 1 billion times greater than
the air pressure at sea level on Earth.
The radiation layer, which is next to
the core, moves the energy produced in
the core in every direction. It can take
millions of years for energy to move
out of this layer.
In the convection layer, gases with
different energies move in circles in
a way similar to air with different
densities. Energy moves out of this
layer in about a week.
The photosphere is the visible surface
of the Sun. It is not a solid surface, but
rather a layer of gases. The photosphere
is cooler than the core. Its temperature
is about 5,730°C (10,346°F).
The next layer of the Sun is the
chromosphere, or the inner layer of
the Sun’s atmosphere. When it can be
seen, it looks like a red circle around
the Sun.
The corona is the outermost layer
of the Sun’s atmosphere. The corona
takes on different shapes around the
Sun depending on changes in the
temperature of the photosphere.
photosphere
Layers of the Sun
corona
chromosphere
core
radiation layer
convection
layer
414
EXPLAIN
Solar Flares
Solar flares are occasional eruptions
of energy from the Sun’s surface that
stretch far out into space. Sometimes
this energy disrupts satellites,
interfering with TV, radio, and cell
phone communication systems.
Energy from solar flares also causes
displays of different-colored lights
in Earth’s upper atmosphere. These
lights are called the aurora borealis
(uh•RAW•uh bawr•ee•AL•is), or northern
lights, in the Northern Hemisphere.
Seen frequently in Alaska and Canada,
they are seen in the southern United
States after large solar flare eruptions.
Solar flares are often associated
with sunspots. Sunspots, or dark spots
on the Sun, are relatively small regions
of the photosphere that have a lower
temperature than the surrounding
regions.
The Parts of the Sun SI.14, SI.15
Make a Model Use modeling clay
to make a model of the Sun that
includes all of the layers.
Be Careful. Using a plastic
knife, cut away a quarter of your
Sun so you can see into it.
Add sunspots and solar flares
to the surface of your Sun.
Communicate Write a description
of your Sun. Include a color key
to identify the layers.
Quick Check
Draw Conclusions Why does it
take millions of years for energy that
moves in every direction to leave the
radiation layer?
solar flare
Critical Thinking Why is it harmful
to our eyes to look directly at the
Sun?
Read a Diagram
sunspot
What is the layer of the Sun between the
core and the convection layer called?
Clue: Find the labels on the diagram for the
core and for the convection layer, and look
for the name of the layer between them.
415
EXPLAIN
What are constellations?
The Sun is just one of billions and billions of stars in the
universe. Scientists use constellations to map all the stars. A
constellation is a pattern in the night sky formed by a group of
stars. Constellations were used by ancient cultures as seasonal
calendars and for navigation. Native American, Greek, and
Roman cultures name many star patterns after animals,
characters from stories, or familiar objects.
Some constellations, like the Big Dipper and Little
Dipper, are used by modern travelers. These two
constellations point to Polaris, the North Star. If you travel
in the direction of Polaris, you will be moving north. If you
ever become lost, look for Polaris. It will always be directly
north of your location.
Finding Polaris
Read a Diagram
How can you use the Big Dipper
to help you find Polaris?
Clue: Look at the stars in the
bowl of the Big Dipper.
416
EXPLAIN
SI.19
the constellation
Canis Major
Observing Constellations
Sirius
Modern Constellations
Today, astronomers divide the sky
into 88 zones. Each zone includes
a constellation. Many of these 88
constellations are the ancient Greek
and Roman constellations. More
recently, astronomers gave names to
constellations visible in the Southern
Hemisphere. New constellations were
needed because observers in ancient
Greece and Rome could not see any
stars below the southern horizon. The
stars you see depend on your location.
Observe On a clear night,
go outside after dark
and observe the stars.
Be sure to take an adult
with you.
Choose a section of the
night sky, and draw the stars
you see. Find patterns in the stars
that look like something familiar
to you. In your science learning
log, draw what you think each star
pattern resembles.
Create names for your star pattern.
Also in your science learning
log, write stories describing the
characters or objects your star
patterns represent.
Communicate Share your
drawings and stories with your
classmates. Do any of your
constellations match those
observed by other students?
How can you find certain stars in
the night sky? The easiest way is by
looking for the constellation in which it
is located. Rigel, for example, is a star
in the constellation Orion. Find Orion,
and you will locate Rigel.
Quick Check
Draw Conclusions Why did
ancient cultures group stars into
constellations?
Critical Thinking How can a
scientist tell other scientists where a
newly discovered star is located?
Greek constellations
417
EXPLAIN
Star Sizes
Stars come in widely varying sizes. A white dwarf can be as small as Earth.
What are some properties of stars?
Some stars are brighter than others.
Stars appear less bright the farther they
are from Earth. For example, Sirius
(SEER•ee•us) looks brighter to us than
Rigel does. However, Rigel is actually
a much brighter star than Sirius is. Can
you guess which star is closer to Earth?
Sirius is much closer to Earth than
Rigel. Think of two flashlights, one
much brighter than the other. If you
placed them side by side, the difference
in brightness would be easy to see.
However, if you moved the brighter
flashlight much farther from you, it
would seem dimmer. The brightness of
a star is called its magnitude. A star’s
actual brightness is called its absolute
magnitude. How bright a star looks
in Earth’s night sky is its apparent
magnitude. Apparent magnitude
depends on how much light a star gives
off and how far away it is from Earth.
418
EXPLAIN
Another property of stars is color.
A star’s color tells you about its surface
temperature. Think about the coils
inside a toaster. As the coils heat up,
they turn red, then orange, and then
orange-yellow. Red and orange colors
indicate cooler stars. Yellow indicates
hotter stars, and blue-white indicates
the hottest stars.
Stars also differ in size. Our Sun is
an average-sized star. Red supergiants
are the largest stars and white dwarfs
are among the smallest.
Quick Check
Draw Conclusions Why does the
Sun look larger and brighter than
any other star?
Critical Thinking If one star
appears brighter than another, can
you correctly assume it is closer?
Visual Summary
The Sun is a star and
the largest object in
the solar system.
Think, Talk, and Write
Vocabulary An object that produces
thermal and light energy is a(n)
.
Draw Conclusions What might result
from a number of large solar flares?
Text Clues
Parts of the Sun include
the photosphere,
chromosphere, and
corona. Solar flares
occasionally occur.
Polaris is the North
Star. It can help you
find your way if you
are lost.
Make a
Study Guide
Conclusions
Critical Thinking How would Earth be
affected if the Sun stopped producing
thermal and light energy?
Test Prep The Sun is made up of all of
the following materials except which?
A
B
C
D
hydrogen
helium
carbon
steam
Test Prep What would you look for in
order to locate Polaris, the North Star?
Make a trifold
book. Use the
titles shown.
Then summarize
what you have
learned.
A
B
C
D
sunspots
planets
solar flares
constellations
Essential Question What are the
characteristics of the Sun and other
stars?
Writing Link
Math Link
M.8
Helpful or Harmful
Compare Temperatures
Is the Sun helpful or harmful? Write
about some of the things that you can
do because of the Sun’s energy. Write
about ways the Sun can be harmful to
you. Be sure to include safety tips.
The average temperature of the surface
of Earth is 14°C . The surface of the Sun
is 400 times hotter. What is the average
temperature of the surface of the Sun?
-Review Summaries and quizzes online at www.macmillanmh.com
419
EVALUATE
Inquiry Skill:
Observe
The location of an observer determines which
constellations he or she can observe. Some
constellations can only be seen in certain seasons.
For example, the constellation Cygnus, the swan,
is only visible in the Northern Hemisphere in the
summer. What constellations can be observed in
each of the seasons?
▶ Learn It
When you observe, you use one or more of
your senses to learn about the world around you.
It is important to record what you observe and
any measurements you take. Scientists record
their observations so they can share information
with others. You may also want to organize your
observations in a chart or a graph. Then you can see
your information at a glance.
the constellati
on Cygnus
The illustrations on these two pages show the same
view of the night sky as seen in different seasons.
In this activity you will use these images to identify
different seasonal star patterns.
spring
420
EXTEND
summer
▶ Try It
Materials paper, pencil, star chart,
reference materials
Create a table that lists the seasons
(spring, summer, fall, and winter) in
four separate columns.
Using a star chart and other reference
materials, identify the different
seasonal star patterns that you see in
each illustration.
On your table, record the names of the
constellations that you have identified
under the appropriate season.
▶ Apply It
Continue to use your observation skills.
See if you can identify star patterns
in the Louisiana night sky. Go outside
with an adult and observe the stars.
Try to identify as many constellations
as you can. You may want to use a
local star chart and other reference
materials as a guide.
fall
Make a list of the constellations you
observe.
Compare your list of constellations
with those of your classmates.
Did your classmates see the same
constellations?
Use reference materials to see which
constellations are visible in the
Louisiana night sky during the current
season. Does your list of constellations
contain all the constellations on the
list you researched? Was your list
missing any constellations? See if you
can find the constellations you missed
on another night. Why can you only
see some constellations during certain
parts of the year?
winter
ESS.41 Explain why the Moon, Sun, and stars appear to move from east to west
across the sky (ESS-M-C1) SI.3 Use a variety of sources to answer questions
(SI-M-A1) SI.7 Record observations using methods that complement
investigations (e.g., journals, tables, charts) (SI-M-A3)
421
EXTEND