About the Sun . . .
About the Sun . . .
Scientists know great deal about the stars that shine at night. Compared to these other stars, the Sun is actually quite average. Many of the stars that appear so small in the night sky are actually much bigger than our Sun. Others, however, are quite tiny in comparison. Some are much hotter, and some are so cool and dim we can barely see them. But for us on Earth, the Sun is just right!
Did you know that most of the atoms in our bodies were made inside stars?
As the famous scientist and educator Carl Sagan says, we are "star stuff."
The Earth is about 13 thousand kilometers (8000 miles) wide, whereas
the Sun is roughly 1.4 million kilometers (900,000 miles) across.
This means it would take more than 100 Earths to span the width of
the Sun! If the Sun were a hollow ball, you could fit about one
million Earths inside of it!
Another way to understand the distance is to think of driving to the
Sun in a car. If you actually could do this, and drove really fast,
say 60 miles an hour (80 km/hr), it would take
you 176 years
to get there! Light from the Sun takes about 8 minutes to reach the
Earth. If you understand how fast
light travels,
you can recognize that the Sun must be very far away.
The Sun will remain more or less the way it is now for about another
5 billion years. After that, it will exhaust the hydrogen it
currently "burns" and will enter a new phase of existence. During
this phase the Sun will begin "burning" helium and will expand to
about 100 times its current size and become what is called a
red giant.
Once it runs out of helium it will collapse into a much
smaller object called a
white dwarf.
In the past, we know the Sun was a little different than it is now, and
at those times the Earth experienced ice ages. During the most
recent ice age, almost all of Canada and the Northern US was covered
in a huge sheet of ice about a mile thick! (That's about 1.6 km.)
Even recently (the late 1600s)
Europe and North America were a bit cooler than they are
now, experiencing a little ice age, and changes in
the Sun were most likely responsible.
The ozone hole is something different.
Ozone
is important to humans because it shields us from harmful ultraviolet
radiation from the Sun. The chemicals from leaky refrigerators and
air conditioners make their way up in to highest part of the Earth's
atmosphere. Way up there, these chemicals destroy ozone, and
scientists have noticed recently that the layer of ozone in the upper
atmosphere is becoming thin in some places. Scientists must study
this so we can understand why it is occurring, and to take action
now to protect it.
It is interesting, however, that ozone is
considered a pollutant when it is close to the ground. It hurts
plants and trees, and our lungs. But we need it way up high to
shield us from the UV.
Also, learning more about the Sun helps us to understand better
other stars. And this helps us understand better
the universe in which we live.
Some scientists study the Sun using computers to predict what the Sun may
do in the future. Others build special instruments which look at
the Sun and make measurements; they use computers both to collect and
later make sense of the measurements.
The material (small particles) interacts with the Earth's outer atmosphere,
causing the gas in the atmosphere to release light. This light appears
in many different colors (green, blue, and red), and we call
it the aurorae.
In the north they are called aurora boreallis,
or northern lights. In the south they are
called aurora australis, or
southern lights.
During a partial eclipse, you can still see part of the Sun
behind the Moon, so you must not look at it. But,
if you look at shadows from the leaves in trees you'll see they
appear crescent shaped. Ask your teacher to make a pinhole
camera, or project an image of the Sun using a mirror, and
you'll be able to see the Moon blocking the Sun.
During a total eclipse, the bright Sun is completely blocked.
At this time, the outer atmosphere of the Sun, or
corona, becomes visible. During this brief
occurrence, you can look at the corona with your eyes, because it
is a million times dimmer than the Sun. Be very careful though -- even
the slightest portion of the Sun poking past the edge of the Moon can
hurt your eyes!
As you may know, the Moon is much smaller than the Earth, and it cannot
block the Sun from the whole Earth at once. For this reason, eclipses
only affect a small portion of the Earth's surface when they occur.
By the way, during a total eclipse, the stars are also visible!
The Sun also emits harmful
ultraviolet
(UV) radiation, which can damage your skin and eyes.
In fact, any tan is a sign of damage to your skin!
A sunburn may hurt for a while, but damaging your skin over
many years can cause many problems,
including skin cancer. That is
why you should always wear sunscreen of
SPF 15
or higher when you will be out in the Sun for more than a few minutes.
This applies even for cloudy days -- though not as bright as sunny days,
much of the harmful UV light still comes through.
Note that having a tan is little protection from skin damage,
providing an SPF of only about 2.
To help protect your eyes, use sunglasses that filter 100% of UV light.
When you buy glasses,
check for labels that say 100% UV Protection.
People who don't protect their eyes when they are young run the risk
of loss of sight when older, including getting
cataracts .
What is the Sun made of?
How big is the Sun?
How far away is the Sun?
How heavy is the Sun?
How old is the Sun?
How hot is the Sun?
Why do we study the Sun?
How do scientists study the Sun?
What are the aurorae?
What is an eclipse?
Can the Sun be dangerous?
How can you learn more?
Do you know what these words mean? (Quiz yourself!
)
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-Authors of this page.
-Revised 25 January 1996 by webmaster@hao.ucar.edu.
Copyright 1995, NCAR.
- Approved by Dick White -
