5. Movement of the Earth

Explain the movements of Earth and describe its effects and importance

Vid 5.1: Earth’s Rotation Animation

We see the sun rise in the east and set in the west every day. Have you ever wondered why the sun seems to be moving?

Well, the sun does not move. It is our Earth that moves.

Fig 5.1: Direction of Sunrise

For example, we get the impression that everything outside is moving when we look out the window of a vehicle that is moving. Everything from the window—houses, mountains, fields, trees—seems to be moving. But do these things move at all? No! The vehicle is the thing that moves. Similarly, the sun, which is fixed, appears to be moving to us because the earth is moving.

There are two movements of the Earth. Let’s learn about them in detail.

Have you ever spun a top? If so, you must have noticed that when a top spins, it rotates around an invisible central line. This invisible or imaginary line is known as the ‘axis’. Our Earth too has an axis on which it rotates.2

Fig 5.2: Earth's Rotation

The movement of Earth on its own axis is called Rotation. Axis is an imaginary line that runs through the centre of the Earth from the North Pole to the South Pole. The axis however, is not a straight line it is slightly tilted at 231/2 Degree. The Earth rotates from west to east and takes 24 hours to complete one full rotation. It moves in an anti clock direction.2

1. What are the effects of rotation?

a. Due to the rotation, the earth experiences day and night.2

b. The half of the earth that faces the sun has day and the other half has night.2

c. The sun rises in the east and sets in the west due to the rotation of the Earth from east to west.2

d. If the Earth does not rotate, one half of the earth will become hot and bright, while the other half will remain dark and frozen2.

e. Earth’s rotation also affects shadows, ocean currents, and wind patterns.2

Fig 5.3: Day and night caused by rotation

2. Why is rotation important?

As the Earth spins, every part of its surface takes its turn to face the sun and receive its warmth. This is crucial for all life on our planet. The sun's impact is far-reaching, influencing everything from the weather patterns we encounter to the food we consume, and even our well-being. Without Earth's rotation, one hemisphere would consistently remain hot and illuminated, while the other would be frozen and out of light.2

As the Earth rotates on its axis, it also moves around the sun on the fixed path. The movement of the Earth around the Sun on a fixed path is called revolution. This fixed path is called the orbit. The Earth’s orbit is not round but is elliptical.3 The earth takes 365 days and 6 hours to complete one revolution. In a calendar year, we normally round the days to 365. The remaining 6 hours of each year are added after four years thus making one extra day in the fourth year. This year is called the leap year. Approximately, every four years, February has 29 days instead of 28. So, there are 366 days in leap year.4

1. What are the effects of revolution?

The revolution of Earth causes the seasons. As the Earth's axis tilts at 23.5 degrees while orbiting the sun, a portion of the planet comes closer to the sun. In other words, the two hemispheres do not receive the same quantity of sunshine.5

Vid 5.2: Effects of the Movement of Earth6

Fig 5.4: Revolution causing seasons

When there is summer in the northern hemisphere, there is winter in the southern hemisphere. Likewise, when there is winter in the northern hemisphere, there is summer in the southern hemisphere.5

Fig 5.5: Summer in the northern hemisphere

Fig 5.6: Winter in the northern hemisphere

Fig. 5.7: Seasons in different hemispheres.

There are times during Earth’s revolution when both the hemispheres are at equal distance from the sun, i.e. neither tilted towards the sun nor away from it. These are the times when we experience the spring season and autumn season5.

2. Why is revolution important?

Earth's revolution creates the changing seasons we experience. This cycle of seasons is vital for the balance of ecosystems and influences plant growth, animal behaviour, and overall climate patterns.
The revolution of Earth helps control the Earth’s temperature. As the planet moves closer to or farther away from the sun during its orbit, it experiences variations in solar radiation.9

Read each bubble and identify if the information is describing the rotation or revolution of the Earth. Drag and drop the animated icons given below to their respective bubbles.

The movement of the Earth plays a significant role in the occurrence of eclipses. Earth’s orbit around the Sun and its rotation on its axis, contribute to the occurrence, timing, and visibility of eclipses. Eclipses happen when the Moon, Earth, and Sun align in a specific way, casting shadows on one another.10

1. What are eclipses?

There are many movements that take place in our solar system. The planets are continually moving around the sun at different speeds. Sometimes one heavenly body such as a moon or planet moves into the shadow of another heavenly body. This is when an Eclipse occurs.

There are two types of eclipse that take place10.
a. Solar Eclipse
b. Lunar Eclipse

a. Solar Eclipse

The moon rotates around the Earth. As the Moon orbits the Earth, it sometimes passes between the Sun and the Earth. At this position the moon blocks the light of the sun from reaching Earth thus, casting a shadow on the parts of Earth. This results in a solar eclipse or eclipse of the sun10.

Fig. 5.8: Solar Eclipse

b. Lunar Eclipse

The Moon moves in an orbit around Earth. At the same time, Earth orbits the Sun. When the Earth comes between the Sun and the Moon, causing the Moon to pass through Earth's shadow, a lunar eclipse occurs. Instead of light hitting the Moon's surface, Earth's shadow falls on the Moon. This is an eclipse of the Moon, or a lunar eclipse. A lunar eclipse can occur only when the Moon is full.10

Fig. 5.9: Lunar Eclipse

Glossary

invisible: something that cannot be seen
illuminate: to shine or brighten with light
elliptical: not exactly a circle but an oval shape, like an egg

Summary:

There are two movements of the planet Earth : Rotation and Revolution.
The movement of Earth on its own axis is called rotation. Due to the rotation, the Earth experiences day and night.
The movement of earth around the sun on a fixed path is called revolution. The revolution of earth causes seasons.
Eclipses happen when the Moon, Earth, and Sun align in a specific way, casting shadows on one another. There are two types of eclipse: Solar Eclipse and Lunar Eclipse.