3rd Class Science Our Universe Formation of Day and Night

       Formation of Day and Night

Look at the following picture that shows the formation of day and night:

The earth not only moves around the Sun in an orbit, but also rotates on its own axis. This is known as rotation. Many countries are there on this planet.

Part of the earth which faces Sun during rotation has day, while the portion on the back side is in dark and has night at that time. After few hours, the illuminated part turn away from Sun and has night, while the dark portion becomes illuminated with sun's light and has day. This cycle repeats. Every part has both day and night in 24 hours. The Earth rotates from west to east, hence the Sun appears to rise from east and sets in west.  

       Formation of Season

Look at the following picture of revolution of the earth around the Sun:

Like other planets, earth also revolves around the Sun in an orbit, which is known as revolution of the earth. Earth completes one round around the sun in 365 days or 1 year. The Earth is divided into two halves by an imaginary line which is called equator.

Look at the following picture that shows the equator of the Earth:

The Earth is tilled on its axis. Its bend portion gets direct heat and light from Sun as compared to the back portion, which receives slanted sun?s rays. The part of hemisphere receiving direct sun's rays have summer. At the same time part of hemisphere receiving slanting rays have winter. Summer has longer days and shorter nights and winter has longer nights and shorter days. When our hemisphere is tilted away from the sun we have winter and the other hemisphere has summer. This cycle is repeated every year. But at all the time of the year suns rays fall directly on the equator. Equator, therefore has same season throughout the year.  

     The given figure represents of which one of the following?

(a) Seasons formation

(b) Day and night formation

(c) Revolution

(d) Both (b) and (c)

(e) None of these

Answer: (B)

Explanation

During the rotation of the earth on its own axis, the part which receives the light of the sun has day and the opposite part has night. Therefore, option (b) is correct and rest of the options is incorrect.

      Which one of the following is responsible for occurrence of season?

(a) Rotation of the earth around its own axis

(b) Revolution of the earth around the sun

(c) Tilting of earth's axis  

(d) Both (a) and (c)

(e) All of these

Answer: (B)

Explanation

Due to revolution, one part of earth gets more heat and light and has summer during that period. The part away from the sun receives less heat and has winter during that period. Therefore, option (b) is correct and rest of the options is incorrect.

There are about 10000 billion stars in the universe.

The earth is about 4.6 billion years old.

Nicholas Copernicus, a polish astronomer first suggested that the earth is revolving around the Sun.

Moon takes 27.3 days to revolve around the earth once.   

The surface temperature of the Sun is near about 5500°c.

Stars are mostly made up of two gases hydrogen and helium.

Andromeda is the biggest galaxy near the Milky Way.

The night sky is divided into 88 different star patterns.

Pole star is the only star which doesn't appear to move.