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Introduction

Weather is the day-to-day change in the blanket of air

that surrounds Earth. This blanket of air is called the

atmosphere. Changes in the atmosphere bring about

changes in the weather. Changes in temperature, wind,

rain, and sunshine are all part of the weather of a place.

We describe the weather in many different ways, such as

sunny and warm, rainy and windy, or snowy and cold. At

any time, the weather is different at different places on

Earth. It may be rainy in one place, but sunny in another.

Weather affects our lives every day. To know what clothes

to wear or whether to stay inside or

go outdoors, we need to know

what the weather will be like.

Scientists who study the

weather try to forecast or

predict what the weather

might do next.

Weather takes place in the lowest

layer of Earth’s atmosphere.

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The sun is a huge,

glowing ball of

burning gas.

One Sun

Our planet Earth moves around one sun. The sun is a

huge, glowing ball of fire. It is the nearest star to Earth

and gives it heat and light. The temperature at the centre

of the sun is about 15 million degrees Celsius.

The weather on Earth is caused by the heat it gets from

the sun. As Earth moves around the sun, different parts

get different amounts of heat. Because Earth’s surface is

curved, the sun’s rays do not hit all parts of Earth in the

same way. The sun’s rays hit some parts of Earth more

directly than others.

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Earth’s Poles

Earth can be divided into two equal parts by an imaginary

line. This line is called the equator. The equator runs

across Earth’s centre. Places on Earth closest to the

equator are the warmest. This is because these places get

the most direct rays from the sun. It gets colder the further

away a place is from the equator. Along the equator, days

and nights are always the same length.

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Equator

North Pole

South Pole

Axis

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Land around Earth’s poles

is covered with ice.

Two Poles

Earth has two poles, called the North Pole and the South

Pole. They are the two ends of an imaginary line called

Earth’s axis. Earth is always spinning, or rotating, on this

axis. The axis passes through the centre of Earth and ends

at either pole. The north end of the axis is the North Pole

and the south end of the axis is the South Pole.

The two poles are the coldest places on Earth. This is

because the sun’s rays do not hit Earth directly at the

poles. So, very little heat from the sun reaches Earth

at the poles.

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Three Steps in the Water Cycle

The water on Earth moves in a cycle from the rivers, lakes,

and oceans to the air, to the land, and back to the rivers,

lakes, and oceans again. This is called the water cycle.

There are three main steps in the water cycle.

In the first step, the sun’s heat causes water to rise, or

evaporate, into the air as moist vapour. The water changes

from liquid water to invisible water vapour. This is called

evaporation. The sun’s heat also causes plants to lose

water through their leaves. This is called transpiration.

In the second step, the moisture meets colder air above.

The vapour grows cooler and condenses to form a cloud

of water droplets. This is called condensation. When the

droplets in a cloud are too heavy, the water falls back to

Earth as rain or snow. This step is called precipitation. It

may fall on land, or in the rivers, lakes, and oceans. If it

falls on land, it will either run back into the rivers, lakes,

and oceans, or soak into the soil to become groundwater.

Because water moves in a cycle, the amount of water on

Earth is always the same.

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