Download The Sun is our local star.

KEY CONCEPT
The Sun is our local star.
Sunshine State
STANDARDS
SC.B.1.3.3: The student
knows the various
forms in which energy
comes to Earth from
the Sun (e.g., visible
light, infrared, and
microwave).
SC.H.1.3.2: The student
knows that the study
of the events that led
scientists to discoveries
can provide information about the inquiry
process and its effects.
SC.H.2.3.1: The student
recognizes that patterns exist within and
across systems.
BEFORE, you learned
NOW, you will learn
• There are different wavelengths
of electromagnetic radiation
• The Sun provides light in
the solar system
• How the Sun produces energy
• How energy flows through the
Sun’s layers
• About solar features and
solar wind
EXPLORE Solar Atmosphere
How can blocking light reveal dim features?
MATERIALS
PROCEDURE
1
Unbend the paper clip and use it to make
a tiny hole in the center of the card.
2 Turn on the lamp, and briefly try to read
• small paper clip
• index card
• lamp with
45-watt bulb
the writing on the bulb.
3 Close one eye, and hold the card in
FCAT VOCABULARY
convection p. 780
VOCABULARY
fusion p. 780
corona p. 780
sunspot p. 782
solar wind p. 783
front of your other eye. Through the hole,
try to read the writing on the bulb.
WHAT DO YOU THINK?
• How did looking through the hole affect
your view of the writing?
• How might a solar eclipse affect your
view of the Sun’s dim outermost layer?
The Sun produces energy from hydrogen.
MAIN IDEA AND DETAILS
You could record information about the Sun by
using a main idea and
details table.
The Sun is the only star in our solar system. Astronomers have been
able to study the Sun in more detail than other stars because it is much
closer to Earth. As a result, they have learned a great deal about its size
and composition and the way it produces energy.
The Sun is far larger than any of the planets. It contains 99.9 percent
of the mass of the entire solar system. For comparison, imagine that
Earth had the mass of a sparrow; then the Sun would have the mass of
an elephant.
The Sun consists mostly of hydrogen gas. Energy is produced when
hydrogen in the Sun’s interior turns into helium. This energy is the
source of light and warmth that make life possible on Earth.
Chapter 22: Stars, Galaxies, and the Universe 779
Energy flows through the Sun’s layers.
FLORIDA
Content Review
reminder
Remember that life on Earth
totally depends on energy
from the Sun, which you
learned in grade 6.
Although the Sun is made entirely of gas, it does have a structure.
Energy produced in the center of the Sun flows out through the Sun’s
layers in different forms, including visible light.
The Sun’s Interior
The Sun’s interior generally becomes cooler and less dense as you
move away from the center.
reminder
1
The center of the Sun, called the core, is made of very dense
gas. Temperatures reach about 15 million degrees Celsius. Under
these extreme conditions, some hydrogen particles collide and
combine to form helium in a process called fusion. The process
releases energy that travels through the core by radiation.
2
Radiative Zone
3
In the convection zone, energy moves mainly by
convection. Convection is the transfer of energy from place to
place by the motion of heated gas or liquid. Rising currents of hot
gas in the convection zone carry energy toward the Sun’s surface.
Remember that radiation
is energy that travels across
distances as electromagnetic
waves.
Core
Energy from the core moves by radiation through
a thick layer called the radiative zone. Although this layer is very
hot and dense, conditions in the radiative zone are not extreme
enough for fusion to occur.
Convection Zone
check your reading
SIMULATION
CLASSZONE.COM
View the Sun at different
wavelengths.
780 Unit 6: Space Science
Where does the Sun’s energy come from?
The Sun’s Atmosphere
The Sun’s outer layers are called its atmosphere. These layers are much
less dense than the interior. The atmosphere generally becomes hotter
and less dense as you move outward.
4
Photosphere Visible light moves by radiation out into space from
the photosphere. It takes about eight minutes for the light to reach
Earth. Since the photosphere is the layer you see in photographs of
the Sun, it is often called the Sun’s surface. Convection currents
beneath the photosphere cause it to have a bumpy texture.
5
The chromosphere is the thin middle layer of the
Sun’s atmosphere. It gives off a pinkish light.
6
The Sun’s outermost layer is called the corona. The corona,
which varies in shape, extends outward several million kilometers.
Both the chromosphere and the corona are much hotter than the
photosphere. However, they have such low densities that you can
see their light only during a total eclipse of the Sun, when the
Moon blocks the much brighter light from the photosphere.
Chromosphere
Corona
Layers of the Sun
Energy produced by fusion in the Sun’s
core flows out through its layers.
prominence
1
Energy is produced in
the Sun’s core.
sunspots
2
Energy moves by radiation through the
radiative zone.
3
Currents of hot gas in
the convection
zone carry energy
outward.
4
The photosphere is
the visible layer of
the Sun.
5
The chromosphere
is the middle layer of
the Sun’s atmosphere.
6
The corona, the
Sun’s outermost layer,
has a very low density.
Corona
Energy travels by radiation
and convection from the
Sun’s core out into space.
During a solar eclipse, the corona
becomes visible because the much
brighter photosphere is hidden.
The corona varies in shape.
Chapter 22: Stars, Galaxies, and the Universe 781
Features on the Sun
Astronomers have observed features on the Sun that vary over time.
Near the Sun’s surface there are regions of magnetic force called magnetic fields. These magnetic fields get twisted into different positions
as the Sun rotates. Features appear on the surface in areas where strong
magnetic fields are located.
are spots on the photosphere that are cooler than
surrounding areas. Although they appear dark, sunspots are actually
bright. They only seem dim because the rest of the photosphere is
so much brighter.
Sunspots
Sunspot activity follows a pattern that lasts about 11 years. At the
peak of the cycle, dozens of sunspots may appear. During periods of
low activity, there may not be any sunspots.
Sunspots move across the Sun’s surface as it rotates. Astronomers
first realized that the Sun rotates when they noticed this movement.
Because the Sun is not solid, some parts rotate faster than others.
Other solar features include flares and prominences (PRAHM-uhnuhn-sihz). Flares are eruptions of hot gas from the Sun’s surface.
They usually occur near sunspots. Prominences are huge loops of
glowing gas that extend into the corona. They occur where magnetic
fields connecting sunspots soar into the outer atmosphere.
check your reading
How are sunspots different from other areas of the photosphere?
Solar Features
Features on the Sun appear in areas where a magnetic field is strong.
Sunspots
Prominences
Sunspots on the photosphere can be
larger than Earth.
Prominences can soar more than 100,000
kilometers above the photosphere.
782 Unit 6: Space Science
Solar Wind
Material in the Sun’s corona is
continually streaming out into space.
The electrically charged particles that
flow out in all directions from the
corona are called the solar wind.
The solar wind extends throughout
our solar system.
Most of the solar wind flowing
toward Earth is safely guided around
the planet by Earth’s magnetic field.
When solar-wind particles do enter the
upper atmosphere, they release energy, which can produce beautiful
patterns of glowing light in the sky. Such displays of light are called
auroras (uh-RAWR-uhz), or the northern and southern lights.
Auroras often occur near the poles.
This circular green aurora
occurred over Alaska
when particles from
the solar wind entered
the atmosphere.
Earth’s atmosphere usually prevents charged particles from reaching
the surface. However, during the peak of the sunspot cycle, flares and
other kinds of solar activity release strong bursts of charged particles
into the solar wind. These bursts, called magnetic storms, can disrupt
electric-power delivery across large regions by causing surges in power
lines. They can also interfere with radio communication.
Magnetic storms are much more harmful above the protective layers
of Earth’s atmosphere. Bursts of particles in the solar wind can damage
or destroy orbiting satellites. The solar wind also poses a danger to
astronauts during space flights.
check your reading
What causes auroras to form?
KEY CONCEPTS
CRITICAL THINKING
1. How does the Sun produce
energy?
4. Analyze Why is the core the
only layer of the Sun where
energy is produced?
2. How does energy move from
the Sun’s core to the
photosphere?
3. How does the solar wind
normally affect Earth?
CHALLENGE
5. Compare and Contrast
Make a diagram comparing
sunspots, flares, and
prominences.
6. Infer A communications
satellite stops working while in
orbit, and a surge in an electric
power line causes blackouts in
cities across a large region.
What probably happened in
the Sun’s atmosphere shortly
before these events?
Chapter 22: Stars, Galaxies, and the Universe 783