Download Click to Preview - Stanford House HK

A Weather Counting Book_Cvr_SI.i2-3 2-3
15/3/06 4:03:22 PM
Y
s' L
er ON
ch n
ea tio
r t ec
Fo sp
in
A Weather Counting Book_Txt_SI.i3 3
7/2/06 2:17:26 PM
Y
s' L
er ON
ch n
ea tio
r t ec
Fo sp
in
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.
A Weather Counting Book_Txt_SI.i4 4
6/2/06 4:57:46 PM
Y
s' L
er ON
ch n
ea tio
r t ec
Fo sp
in
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.
The sun is a huge,
glowing ball of
burning gas.
A Weather Counting Book_Txt_SI.i5 5
6/2/06 4:58:01 PM
Y
s' L
er ON
ch n
ea tio
r t ec
Fo sp
in
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.
Earth’s Poles
North Pole
Axis
Equator
South Pole
A Weather Counting Book_Txt_SI.i6 6
6/2/06 4:58:15 PM
Y
s' L
er ON
ch n
ea tio
r t ec
Fo sp
in
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.
Land around Earth’s poles
is covered with ice.
A Weather Counting Book_Txt_SI.i7 7
6/2/06 4:58:31 PM
Y
s' L
er ON
ch n
ea tio
r t ec
Fo sp
in
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.
A Weather Counting Book_Txt_SI.i8 8
14/3/06 4:03:17 PM