Download Section 27.1

UNIT NINE: Matter and Motion
in the Universe
 Chapter 26 The Solar System
 Chapter 27 Stars
 Chapter 28 Exploring the Universe
Chapter Twenty-Seven: Stars
 27.1 The Sun
 27.2 Stars
 27.3 The Life Cycle of Stars
Chapter 27.1 Learning Goals
 Explore the properties of the Sun.
 Identify unique zones of the Sun and describe
what happens in each area.
 Discuss applications of solar energy.
27.1 The Sun
 The Sun is is a giant,
hot ball of gas held
together by gravity.
 The Sun is mediumsized compared with
other stars in the
universe.
Approximately 1 million
planet Earths could fit
inside the Sun!
27.1 The Sun
 Gravity squeezes the
density of a star so
tightly in the core that
the electrons are
stripped away and the
bare nuclei of atoms
almost touch each other.
 Nuclear fusion occurs.
27.1 The Sun
 In the process, huge
amounts of energy are
given off.
 Because of its mass,
the Sun’s gravitational
force is strong enough
to hold the entire solar
system in orbit.
27.1 Anatomy of the sun
 The apparent surface of
the Sun that we can see
from a distance is
called the photosphere,
which means “sphere
of light.”
 Just above it is the
chromosphere.
 This is a very hot layer
of plasma, a highenergy state of matter.
27.1 Anatomy of the sun

The corona is the
outermost layer of the
sun’s atmosphere,
extending millions of
kilometers beyond the sun.

Sunspots are areas of gas
that are cooler than the
gases around them.
27.1 Features of the sun
 Occasionally, large
“loops” of gas
called prominences
can be seen
jumping up from
groups of
sunspots.
27.1 Features of the sun
 Solar wind is an
electrically charged
mixture of protons and
electrons that cause
magnetic storms.
 Auroras, called the
northern lights, occur
when layers of our
atmosphere are
energized by solar
winds.
27.1 Solar energy
 Solar energy is a term that refers to
radiant energy from the Sun.
 The radiant energy of the Sun reaches
Earth in the form of electromagnetic
waves.
 We can use solar energy to heat
buildings and generate electricity.
27.1 Solar energy
 Buildings that use
passive solar heating
are designed to trap
sunlight.
 Glass traps warm air,
causing a
“greenhouse effect.”
27.1 Solar energy
 Photovoltaic (or PV)
cells are devices that
convert sunlight
directly into electricity.
 Solar cells are found
on calculators,
watches, or certain
outdoor light fixtures.
27.1 More about the Sun’s energy
 In 1905, Albert Einstein proposed that matter
can be converted into energy.
 His famous equation shows how huge
amounts of energy can be created from a
smaller mass.
27.1 More about the Sun’s energy
 The amount of this
energy from the Sun that
reaches the outer edge
of Earth’s atmosphere is
known as the solar
constant.
 The accepted value is
1,386 watts per square
meter (W/m2), or about
thirteen 100-watt light
bulbs per square meter
of surface.
Optional* Investigation 27C
Efficiency of a Solar Cell
 Key Question:
How can we use energy from the sun to
generate electricity?