Worlds of David Darling > Children's
Encyclopedia of Science > The Sun > Chapter 1
THE SUN: Our Neighborhood Star
a book in the Discovering Our Universe series by David Darling
1. A Sun to Live By
"And here is some late news. Leading scientists
from around the world report that something strange is happening to our
Sun. The Sun seems to be disappearing. Life-threatening effects are forecast
for all the people of Earth. More on this in our 10 p.m. report."
What a frightening story this would be to hear on the news – the Sun
disappearing! But could it ever happen? Could the Sun ever just "switch
off"? Happily the answer is no. The Sun has been around for a very long
time. It is in perfectly good health, and it will continue to be around
for a very long time to come.
All the same, let's imagine what would happen if suddenly there were no
Sun. When we do, we realize how much we depend on the Sun for nearly all
Can you think of the two most important things that we get from the Sun?
Step outside on a warm summer's day and you'll have the answer: light and
Without light from the Sun, the Earth would be a terribly gloomy place.
Not only would there be no bright Sun to light up our day, there would be
no cheery Moon at night. The Moon shines simply by reflecting sunlight.
Without a bright Sun or Moon in the sky, only the distant stars would be
left to give a dim glow to our dark world.
Food from the Sun
Do you think we could get used to living on a planet where it was always
dark? Perhaps, but darkness would be the least of our worries. Without sunlight,
all the green plants on Earth would quickly die. For green plants –
and that includes most plants – use sunlight, water, and air to make
food and grow. The way in which they do this is called photosynthesis.
Try an experiment with two small, healthy plants. They can be weeds, shoots
of grass – anything with green leaves. Plant both carefully in good
soil and give them some water. Now, put one of them in a sunny place such
as a windowsill. Put the other in a place that's always dark; for example,
a cupboard or a closet. Keep them both watered and watch what happens as
the days go by.
A dark world with no green plants would be a sad place. But green plants
aren't the only living things that depend on the Sun. Without plants, all
the animals that eat them would die, too! In fact, without sunlight, there
would soon be no cows, no sheep, no type of land animal, bird, insect, or
fish that depended on green plants for food.
All animals eat either plants or the flesh of other animals who have eaten
plants. Without sunlight, then, all forms of life on Earth – including
people – would quickly die from lack of food.
Energy from the Sun
Sunlight is important in other ways, too. At night, for instance, how would
you see to read this book? You would turn on a light – an electric
light. But where does the electricity to work the light come from? It comes
from your local power plant. And how does the power plant make electricity?
It probably makes it by burning coal, or oil, or natural gas. These are
called fossil fuels and are all found in the ground, where they took a long
time to form.
What have fossil fuels to do with sunlight? Before the age of the dinosaurs,
great forests of strange trees, ferns, and other green plants covered the
land. These forests needed sunlight to grow. In swampy areas, when the plants
died, they sank into the mud. As the mud got thicker and heavier, the ancient
plants were squashed harder. Over millions of years, they turned into coal.
In other places, countless tiny sea animals, which also depended on sunlight
in some way for food, died and fell to the seabed. There they were buried
by thickening layers of mud and sand until, over time, they turned into
oil or into natural gas.
What we are doing, then, when we burn coal, oil, or gas, is freeing the
energy in sunlight that was trapped millions and millions of years ago by
green plants! Strange as it may seem, most of our modern world runs on energy
left to us long ago by the Sun.
We know that fossil fuels took millions of years to form. Today, in our
cars, planes, homes, and factories, we are using them up far faster than
they can ever be replaced. What new forms of energy will we find to replace
the disappearing fossil fuels? Many of them will, again, depend on the Sun.
We are learning how to use the Sun's energy directly to heat our buildings
and to make electricity. Perhaps you have seen houses or schools in your
neighborhood with solar collectors used for trapping heat from the Sun.
Most spacecraft used electricity made from sunlight by solar cells.
In the future, we might use giant curved mirrors, or groups of mirrors,
to focus the Sun's rays. In that way we may make a great deal of electricity.
But whether we use them wisely or not, light and heat from the Sun will
continue to pour onto the Earth every day – just as they have for
the last few billion years.
Weather from the Sun
The Sun's heat is just as important to us as its light. Without heat from
the Sun, the Earth would become deadly cold. The oceans would freeze, and
the temperature would drop below that of the worst Arctic winter.
Heat from the Sun controls our weather, too. During the day, the Sun's rays
warm the land and ocean, which in turn warm the air above them. The warm
air then moves both north and south to cooler regions, giving rise to winds.
As the Sun heats the ocean, it also turns some of the water into water vapor.
The mist-like vapor rises, cools, and eventually forms clouds. If the little
water drops that make up the clouds grow big enough, they fall as rain.
Our weather, our fuels, our very lives depend so much on the Sun. But what
is the Sun? Where did it come from? And what will happen to it in the distant