|
Believe it or not, the Sun is just a
star,
just like those we see
twinkling
at night. The Sun, however, is so much closer to us
on Earth that it looks much bigger, much brighter, and we can
even feel heat coming from it.
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!
The Sun is made of hot
gases,
containing many of the same materials we find here on the Earth.
These materials, called
elements,
include hydrogen, helium, calcium, sodium, magnesium, and iron.
You can find all of these on any
periodic table of elements.
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 Sun is HUGE!
Even though it looks small in the sky it is actually bigger than you
might imagine. It only looks small because it is 93
million miles away. (That's about 150 million km.)
The Earth is very tiny
compared to the Sun. In fact, if you think of the Sun as a
basketball, the Earth would only be the size of the head of a pin
-- a mere speck.
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!
The Sun is very FAR from Earth.
In fact,
it is 93 million miles away. (That's about 150
million km.)
If the Sun were the
size of a basketball, and Earth the size of the head of a pin, the
basketball and the pin would be separated by about 100 feet -- a third
of a football field (30.5 meters). If you were standing at the
basketball (and
didn't have a telescope to help you), you wouldn't even be able to see
the pinhead Earth.
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.
Although we cannot actually weigh the Sun with a
scale, we can compute its weight by studying the way it affects other
objects, like the Earth. We do know that it contains virtually
all the mass in our solar system! We can also
understand this better by making some comparisons. Since the Sun
is so much more massive than the Earth (over 300,000 times heavier)
its gravitational pull is also much larger. A child that weighs 75
pounds on Earth would weigh about a ton on the Sun.
The weight increases by a factor of 30.
(Of course, we cannot really stand on the Sun, for it is too hot and
has no solid surface.)
The Sun is about 4 1/2 billion years old.
Humans have only been
around for a tiny, tiny fraction of this time. As a comparison, if
you think of 4.5 billion years as the length of a 12 inch ruler, then
the time humans have existed wouldn't even be the width of the lines
marking the inches. (Metric equivalent is 30.5cm and it would
still be just the width of the markings.)
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.
The Sun is extremely HOT!
The middle of the Sun is at least
10 million degrees. The
"surface" of the Sun (what we see) is only 5800 degrees. This is cool
for the Sun, but is actually about 16 times hotter than boiling water
(ouch!). The outer atmosphere of the Sun (which we don't really see
with our eyes) gets extremely hot again, about 1.5 to 2 million
degrees. These huge temperature changes are very interesting to
scientists.
Never look directly at the Sun,
even with sunglasses. The human
eye is not made to look at an object that bright. It is so bright
it could easily blind you in just a few seconds. Have you ever
looked at a bright light bulb and then had to look away after a short
time? Well, the Sun is about a million times brighter than a
household light bulb. This is why you can injure your eyes: if you
look directly at the Sun, the inside of your eyes can burn severely
and may never heal again. You could lose your sight permanently. In
order to study the Sun,
scientists look directly at the Sun only
with the aid of special instruments that are made to tolerate the
extreme brightness.
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 .
Without the Sun, life on Earth would not exist. Our planet would
be a frozen dark ball, drifting dead in space.
We need the Sun for light, heat and energy. With the
Sun, plants can grow, and animals can eat.
The Sun's output changes over time. These changes affect not only
our daily lives and climate, but also
our communications, such as by satellites.
The more we know about the Sun, the better we can deal with these changes.
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.
Studying the Sun and how it affects the Earth is a very complicated
process. In order to successfully do this, scientists approach the
problem in many different ways. They separate their scientific
efforts into categories and usually specialize in specific areas,
such as How the amount of light from the Sun varies over
time, or How the Sun's light affects the Earth's
climate.
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 Aurora are colorful, whispy, moving curtains of light that occur
in the night sky near one the Earth's poles. This light moves around
in and changes color in a dazzling dance of light.
The aurora are caused by energetic particles coming from the Sun. The
Sun is very active, always putting stuff out into space. Every once
in a while it can suddenly eject material -- a million tons of it
-- into space. Some of this comes towards the Earth and hits our
atmosphere.
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.
Periodically the Moon will move directly in front of the the Sun.
When it does, it blocks the light coming from the Sun. If it blocks
out the Sun totally, we call this a total eclipse.
If the Moon only blocks part of the Sun, it is a partial
eclipse. You may wish to visit a
real total eclipse,
observed from the South American country Chile in 1994.
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!
|
