Maharashtra Board Class 4 EVS Chapter 16 Day and Night PDF Download

Day and Night

Shevanta wakes up at a quarter to seven every morning.

What differences do you see in the two pictures? What causes these differences?

We live on the earth. The earth gets light from the sun. The earth's shape is like that of a very large ball. Therefore, light from the sun does not reach the entire earth at once and the same time. Half the earth gets sunlight while the other half remains dark.

We say that it is day in the half that gets light, while in the other half where sunlight does not reach, it is night. Every day we see day chasing night and then night chasing day. Night comes after day and then day follows night. This cycle goes on without stopping. What could be the reason for this?

Just as a top spins about itself, the earth, too, turns around itself. So, the part of the earth that is getting sunlight goes into darkness and the part that is in darkness comes into the light. That is, where there is day it becomes night after some time and where there is night, it becomes day.

The sun rises in the east in the morning and moves towards the west. In the evening, the sun sets in the west. So we feel that the sun goes around the earth. But that is only an impression. Actually, the earth turns around itself. That is why we have day and night on the earth.

This spinning of the earth around itself is called the rotation of the earth.

Teacher's Note

You can see the sun rise in the east every morning from your house. The sun does not really move. The earth is spinning, just like a spinning top. This is why we see day and night.

Exam Trick

Remember: Rotation = earth spinning like a top. The sun stays in one place. We move around the sun. Think of a merry-go-round at a fair - you spin, not the world outside.

Points to Remember

The earth is round like a ball.
Half the earth gets sunlight at one time. The other half is dark.
Day is when sunlight reaches your place. Night is when your place faces away from the sun.
The earth spins around itself. This is called rotation.
Rotation of the earth causes day and night.

The whole day has 24 hours. But, are there always twelve hours of daylight and twelve hours of darkness? If that were true we would have sunrise every morning at six o'clock and sunset every evening at six o'clock, too.

Let us see what really happens.

Some calendars give the times of sunrise and sunset for every day. Take such a calendar for this year and use it to complete the following tables.

What do you see?

In November, the sun rises a little later every day while it sets a little earlier every day.

In the month of May, the sun rises a little earlier every day and sets a little later every day.

What does this tell us?

In November, the days becomes shorter and shorter, while nights become longer.

In May, the days become longer and longer while the nights become shorter and shorter.

Thus, we are now sure that day and night are not of 12 hours each all year round.

In the whole year, 22 March and 22 September are the only dates on which day and night are of equal length, that is, of 12 hours each.

Teacher's Note

In India, summer is very hot with long days. Winter is cold with long nights. In March and September, days and nights are equal. You can check this in your school calendar.

Exam Trick

Remember: March 22 and September 22 are the only two days with 12-hour day and 12-hour night. On all other days, they are not equal. Use these two dates to answer exam questions.

Points to Remember

A full day has 24 hours.
Day length and night length change every day.
Only on March 22 and September 22 are day and night both 12 hours long.
In May, days are longer and nights are shorter.
In November, days are shorter and nights are longer.

When the days are longer and the nights are shorter, it is summer.

When the nights are longer and the days are shorter, it is winter.

On March 22, day and night are both 12 hours long. Then, in our part of the earth, day time increases slowly and night time decreases. This goes on till June 21. On June 21, our day is the longest and the night is the shortest.

From June 21, in our part of the earth, day time becomes shorter and shorter and nights become longer. This goes on till September 22. On September 22, our day is of 12 hours and the night too is of 12 hours. After that, the days continue to become shorter. The nights become longer. This goes on till December 22.

On December 22, our night is the longest and the day is the shortest. From December 22, the day grows longer and the night, shorter. This goes on till March 22. From March 22, this cycle repeats itself.

Teacher's Note

In India, June 21 is the longest day of the year. December 22 is the longest night. This is why summer is so hot and winter is so cold. You can notice these changes in your own city.

Exam Trick

Remember: June 21 = longest day. December 22 = longest night. The dates repeat every year. Mark these in your calendar for easy memory.

Points to Remember

March 22 = day and night both 12 hours.
June 21 = longest day, shortest night (summer).
September 22 = day and night both 12 hours again.
December 22 = shortest day, longest night (winter).
This cycle repeats every year from March 22 to March 22.

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