Class 5th | The Universe

Class 5th | The Universe

The universe is a huge wide-open space that holds everything with earth from the moon to the stars. 

Astronomers use a special instrument to measure the universe called spectroscope.

Information based on this instrument, scientists have learnt that the universe is still growing outwards in every direction.

THE SUN

The sun is a star. It is a huge hot ball of burning gases. Inside the sun, hydrogen changes into helium gas. This continuous process produces a lot of heat and light in the sun.

It is situated at the centre of the solar system.

Q. What is the source of sun's heat and light?

Ans. Sun

THE MOON

The moon is the earth's only natural satellite. It rotates around its own axis and at the same time revolves around the earth.  

The moon is the brighest object in the night sky. It is approximately 385,000 km away from the earth. 

The moon is cold and dry with rocks and fine dirt on its surface. 

The moon has large circular hollows called craters. 

There is no air and water on the moon (however, scientists at ISRO find presence of water on the moon). So, there can be no weather. Since sound waves travel through air, no sound can be heard on the moon. Hence, there is silence on the moon.

A crater

Since there is no atmosphere surrounding the moon's surface, there is no protection from the strong rays of the sun. This leads to extreme changes in temperature during night and day. The temperature on the moon ranges from a daytime maximum of about 123°C to a night time minimum of about -233°C.

All these features make the moon a place where no life is possible.

Gravity on Moon

The moon's gravity is one-sixth of the gravity of the earth. On the moon, you would be able to lift objects that are very heavy on the earth. If you can jump one metre on the earth, you will be able to jump six metres on the moon.

Why the Moon Shines

The moon does not have its own light. It shines when the sun's light falls on its surface and is reflected back to the earth.

In Figure 1, a clear shadow is formed behind the bag. A shadow is formed since light cannot pass through the bag. Such objects through which light does not pass are called opaque objects.

In Figure 2, a faint shadow of the butter paper is formed. The shadow is faint since some light can pass through the butter paper. Such objects through which some light can pass are called translucent objects.

In Figure 3, no shadow of the glass is formed as all the light passes through it. Such objects are called transparent objects.

ECLIPSES

The moon and the earth are opaque objects. They cast shadows when light falls on them. When the sun, the earth and the moon come in straight line, the light of the sun is blocked by the moon or the earth then the shadow of the one is formed on the other. This is called an eclipse. An eclipse is the casting of shadow by one celestial body on the other in the space. Eclipses are of two types - Solar eclipse and lunar eclipse.

Solar eclipse

When the moon comes between the sun and the earth, it casts its shadow on the earth. To the people who fall under this shadow, the sun gets blocked. The sky becomes dark even though it is daytime. This is called solar eclipse.

Sun

Moon

Earth

Diagram showing solar eclipse

A solar eclipse occurs on a new moon day, only when the sun, the moon and the earth come in one row. Let us do an activity.