The Children's Encyclopedia
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 we have.
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 heat.
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
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 future?