Download The Sun

The Sun: Our Most
Important Star
If the Sun did not exist, there would be no life on
Earth. The Sun plays vital roles in most of the
processes on Earth, as well as in every life on
Earth. The Sun provides plants with energy for
photosynthesis. It is also the basis for birds’
migration schedules. Sunlight is even the essential
ingredient that helps human beings make vitamins
that are necessary for healthy bodies.
An Interesting Star
The Sun is not a planet like Earth; it is a star. At an
The Sun is much bigger than the other
average distance of 93,000,000 miles away, the
objects in the Solar System. Compared to
other stars, however, the Sun is merely
Sun is Earth’s closest star. This is why the Sun is
bigger than other stars in the sky. Studying the Sun average in size.
helps people to learn about other stars that are farther away
from Earth.
The Sun is made up of several layers of gas. The
innermost portion of the Sun is the core. The core
is approximately 27,000,000 degrees Fahrenheit
or 15,000,000 degrees Celsius. This extreme heat
causes regular nuclear reactions to take place
inside its core.
The radiation zone surrounds the core and is a
dense layer of gases. This layer is surrounded by a
less-dense layer known as the convective zone. The
convective zone takes its name from the fact that
the gases in this layer constantly move in
convection currents. Warm gases move in towards
The Sun is composed of several layers of
gases.
the core and cooler gases move outward. The part
of the Sun usually seen from Earth is the
photosphere. The two outermost layers of the Sun, the
chromosphere and the corona, are such thin layers of gas that
they can only be seen during a total solar eclipse.
The Sun is almost a perfect sphere, which means it has nearly
the same radius when measured in any direction from its center.
Much like Earth, the Sun rotates on an axis. The Earth rotates
once per day, but the Sun rotates once every 25 days. This slow
Discovery Education Science
© Discovery Communications, LLC
The Sun: Our Most
Important Star
rotation allows this big ball of gas to maintain its perfect
spherical shape.
The Mass of the Sun
The Sun is by far the biggest object in the Solar
System. It measures 875,000 miles wide. The
Sun is responsible for 99.8% of the entire mass
of the Solar System; it could contain
approximately 1.3 million Earths. The Sun may
seem big to people, but compared to red giants
and other massive stars, the Sun is small.
Unraveling the Mystery of the Sun
The Sun is much smaller than a red giant,
which is what it will eventually become.
Up until the 16th century, humans believed that all of the stars,
including the Sun, revolved around the Earth. In 1543, Nicolaus
Copernicus was the first to theorize that the
Sun was the center of the Solar System. His
research was based on the movement of the
stars in the sky. He was also the first to
theorize that the Earth was not stationary.
Instead, Copernicus argued that Earth revolves
around the Sun. Later astronomers, observing
the sky through telescopes, proved Copernicus
correct.
The Sun: Keeper of Life on Earth
The Sun is responsible for many important
processes on Earth that are necessary for our
survival.
Modern telescopes have provided humans
with incredible images of the Sun and the
processes that happen on its surface and in
its atmosphere.
Gravity
Due to its great mass, the Sun has a strong gravitational pull
that keeps Earth in orbit. Without the Sun’s strong pull, Earth
would float out into space.
Food
Plants rely on the Sun for the energy necessary for
photosynthesis, a process that allows plants to make their own
food. If the Sun didn’t exist, plants could not survive. If plants
Discovery Education Science
© Discovery Communications, LLC
The Sun: Our Most
Important Star
did not exists, the animals that depend on them for food—
including humans—could not survive.
Energy
Sunlight is the primary source of energy on the planet. The Sun
produces solar energy that we use in our daily lives. Fossil fuels,
such as natural gas and coal, are made from natural matter
whose existence depended on the light and heat from the Sun.
Climate
Without the heat from the Sun, the Earth would freeze. Heat
from the Sun causes differences in air pressure on Earth, which
in turn cause the wind and weather to change.
Health
Sunlight absorbed through the skin is used by humans to make
vitamin D, an important vitamin for bone health.
The Changing Sun
Much like everything else in the Solar System, the Sun is
constantly changing. Every eleven years, the Sun goes through a
solar cycle, which causes an increase in its magnetic activity.
Scientists can see this activity by observing dark spots on the
Sun’s surface known as sun spots. Solar flares are explosions on
the Sun’s surface. These flares usually occur around active areas,
such as sun spots. These explosions can be strong enough to
affect certain electronic processes on Earth such as long-range
radio communication and radar.
The Future of the Sun
The Sun has existed for four billion years. Scientists predict that
it will continue to burn for approximately another five billion
years. The Sun will then begin to die. The first step in this
process is to transform into a red giant star. The Sun will swell
in size and absorb Mercury, Venus, and Earth. After the red
giant phase, the Sun will lose much of its mass and become a
nebula. Once the core of the nebula cools, all that will remain of
the Sun will be a slowly fading white dwarf star.
Since the death of the Sun, and therefore of Earth, is inevitable,
scientists have already started to look to the future. Several solar
Discovery Education Science
© Discovery Communications, LLC
The Sun: Our Most
Important Star
systems have been identified that may have planets similar to
Earth which revolve around stars much like our own Sun.
Perhaps billions of years from now future humans will look up
at the sky from a different planet and observe a different Sun.
Discovery Education Science
© Discovery Communications, LLC