Page 252 - New Medley 4 Semester 2 PDF (Merged)

Sometimes, the molten rocks in the mantle find a weak spot in the Earth’s crust.

They break through this weak point and the hot boiling liquid called lava, along
with some gases, rushes out of the Earth’s crust. This is called a volcano.

What causes day and night
Axis
The Earth spins just like a top. It spins about North pole
an imaginary line passing through its north and
south poles. This line is called axis of the Earth.

The axis of the Earth is not vertical but it is

slightly tilted.

The spinning of the Earth on its axis is called
rotation. One rotation of the Earth is completed
in 24 hours. During rotation, only half of the South pole

earth is exposed to the sun at a time, while the Rotation of the Earth
other half remains away from the sun. The part Axis North pole

of the Earth facing the sun has daytime while
the part away from the sun has night. Thus, the

rotation of the Earth causes day and night. Northern
hemisphere
There is another imaginary line which divides Equator
Equator
the earth into two equal halves. This imaginary
line is called equator. It lies exactly between the Southern
hemisphere
north and south poles. The two equal halves into
South pole
which the equator divides the Earth are called Northern and Southern hemispheres
Northern and Southern hemispheres.

What causes change in seasons

Besides spinning on its tilted axis, the Earth also moves around the sun on a
fixed path, called orbit. The movement of the Earth in its orbit around the sun

is called revolution. The Earth takes 365 days and 6 hours to complete one
revolution. This duration is called a solar year or simply a year.

Throughout the year, as the Earth orbits the sun, its different parts are in different
positions with respect to the sun. This difference causes change in seasons

at different places on the Earth. At any time, the northern and the southern
hemispheres have opposite seasons. The four main seasons are spring, summer,

autumn and winter.

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