The Earth and Its Movements Chapter Notes | Social Studies Class 4 ICSE PDF Download

Introduction

Our Earth is always moving, just like a spinning top or a ball going around in a circle. In this chapter, we will learn about the two special ways the Earth moves, called rotation and revolution. We will also find out how these movements make day and night and change the seasons. The Earth spins on an invisible line called its axis, and this helps us understand why some places get sunlight while others are dark. Let’s explore how the Earth moves and why it is so important for us!

Movements of the Earth

• The Earth is our home planet, and it is always moving in two ways.
• It spins like a top on its axis, which is called rotation.
• It also moves around the Sun in a fixed path, which is called revolution.
• Both movements happen at the same time.
• These movements are very important for life on Earth to grow and flourish.

Axis of the Earth

• Imagine a spinning top or a ceiling fan; they spin around a point or line. This line is called the axis.
• The Earth also spins around an imaginary line called its axis.
• We can understand the axis by looking at a globe, which is a model of the Earth.
• The globe has a rod that goes through it, and it spins around this rod.
• This rod is the axis of the globe.
• The Earth’s axis is tilted a little, not straight.
• The top end of the axis is called the North Pole.
• The bottom end of the axis is called the South Pole.

Rotation of the Earth

• The Earth spins on its axis from west to east.
• This spinning is called rotation.
• It takes the Earth about 24 hours to complete one full rotation.

Day and Night

• The Earth’s rotation causes day and night.
• When the Earth spins, one part of it faces the Sun and gets light, which is daytime.
• The other part is away from the Sun and is dark, which is nighttime.
• As the Earth keeps spinning, day and night happen one after the other.

Revolution of the Earth

• The Earth moves around the Sun in a fixed path called its orbit.
• The orbit is oval in shape, which means it is elliptical.
• This movement around the Sun is called revolution.
• The Earth takes 365 days and 6 hours to complete one full revolution around the Sun.

Leap Year

• We call a year 365 days long for convenience.
• But the Earth takes 365 days and 6 hours to revolve around the Sun.
• These extra 6 hours are saved every year.
• After four years, these extra hours add up to 24 hours, which is one full day (6 + 6 + 6 + 6 = 24 hours).
• This extra day is added to February every fourth year.
• Normally, February has 28 days, but in the fourth year, it has 29 days. This year with 366 days is called a leap year.

How are Seasons Caused

• The Sun gives heat and sunlight to the Earth all year, but some months are cold, and some are hot.
• This happens because of two reasons:
• Tilt of the Earth’s axis:
  • The Earth’s axis is tilted, so when the Earth moves around the Sun, the part that is tilted toward the Sun gets direct sunlight and becomes hot, experiencing summer.
  • The part that is tilted away from the Sun gets less direct sunlight, so it is colder and experiences winter.
• Revolution of the Earth around the Sun:
  • As the Earth revolves around the Sun, different parts of the Earth get direct sunlight at different times.
  • This causes summer in some areas and winter in others.
  • The Earth is divided into two halves by an imaginary line called the equator.
  • The upper half, from the equator to the North Pole, is called the northern hemisphere.
  • The lower half, from the equator to the South Pole, is called the southern hemisphere.
• When the northern hemisphere is tilted toward the Sun, it gets direct sunlight and has summer.
• At this time, the southern hemisphere is tilted away from the Sun, so it has winter.
• The longest day in the northern hemisphere is on 21 June, which is the summer solstice.
• At the same time, the southern hemisphere has its shortest day and longest night on 21 June, which is the winter solstice.
• When the southern hemisphere is tilted toward the Sun, it gets direct sunlight and has summer.
• At this time, the northern hemisphere is tilted away from the Sun, so it has winter.
• The shortest day in the northern hemisphere is on 22 December, which is the winter solstice.
• At the same time, the southern hemisphere has its longest day on 22 December, which is the summer solstice.
• There are two special times when both hemispheres get equal sunlight from the Sun:
  • On 21 March and 23 September, the Earth’s axis is not tilted toward or away from the Sun.
  • Both hemispheres have equal days and nights on these days, and this is called an equinox.
  • In the northern hemisphere, 21 March is called the spring equinox because it marks the start of spring.
  • Also, 23 September is called the autumnal equinox because it marks the start of autumn.
  • In the southern hemisphere, 21 March is the autumnal equinox, and 23 September is the spring equinox.

Special Case of the Poles

• We can use a globe and a torch to understand what happens at the North Pole and South Pole.
• Spin the globe to show the Earth’s rotation, which causes day and night.
• Shine the torch on the globe to act like the Sun.
• Notice that when the northern half of the globe is tilted toward the light, the North Pole gets sunlight.
• But the North Pole does not get dark at any point because of the tilt of the globe.
• The South Pole stays in darkness during this time. Because of the Earth’s tilt, the North Pole gets sunlight for six months when the northern hemisphere is tilted toward the Sun.
• During these six months, the South Pole stays in darkness.
• When the southern hemisphere is tilted toward the Sun, the South Pole gets sunlight for six months.
• During these six months, the North Pole stays in darkness.

Fun Fact

At the North Pole and South Pole, there are special events because of the Earth’s tilt. When the Sun is seen at midnight, it is called the midnight sun. In areas where there is no sunlight for the whole day, it is called the polar night.

Points To Remember

• The Earth has two movements: rotation and revolution.
• The spinning of the Earth on its axis is called rotation.
• The rotation of the Earth causes day and night.
• The movement of the Earth in a fixed orbit around the Sun is called revolution.
• The Earth takes one year to revolve around the Sun.
• The tilt of the Earth’s axis and its revolution around the Sun cause the seasons.
• Different parts of the Earth experience different seasons because of these movements.

Glossary

• Simultaneously: At the same time
• Flourish: Grow; Develop
• Alternatively: One after the other
• Elliptical: Oval
• Inclined: Tilted