- Books Name
- Class-8 Science Book
- PathSet Publications
- CBSE Class 8
- These are objects which twinkle in the sky at night.
- There is a large number of stars in the sky.
- Sun is the nearest star to our planet which is approx 150 million km away from Earth.
- The distance of the Sun from the Earth may be said to be about 8 light minutes.
It is defined as the distance traveled by light in one year. And it is the unit to measure large distances. The speed of light is about 300,000 km per second.
- The stars are celestial bodies comprising of hot gases (mainly helium and hydrogen).
- All the stars emit their own light.
- All the stars are not the same. They may vary in brightness, size, colours and temperature.
- They are massive in size however they appear as a point-sized object from the Earth’s surface.
- This is so because they are at a huge distance from the earth.
- Stars have a life period. They take millions of years to be born and live for tens of millions of years and eventually come to an end. Due to their long lifespan, the changes in the stars are not very sudden. Hence, they appear as permanent to us.
Why do stars twinkle?
Stars emit light that when entering the earth's surface has to travel through the several layers of the earth’s atmosphere. Hence, it appears that the light is traveling in a zig-zag motion due to the change in densities of the earth’s atmosphere and the density of the space. Therefore, it appears to us as if the stars are twinkling.
Why Sun is a Star?
- The sun is also a star because the sun can produce heat and light energy on its own.
- The sun has a life period just like every other star.
- The sun is estimated to be born around 5 billion years ago and would live for the next 5 billion years.
Distance between the Sun and the Earth
- The sun does not appear as a point-sized object like other stars because the sun is at a close distance to the earth as compared to other stars.
- The distance between the Earth and the Sun is estimated to be 150,000,000 km.
- The star that is closer to the Earth, after the sun, is called Alpha Centauri. The distance between the Earth and the Alpha Centauri is estimated to be 40,000,000,000,000 km.
- The distance between celestial objects is described in light-years.
- A light-year, as the name suggests, is the total distance light travels in 1 year’s time.
- The speed of light = 300,000 km per second
- The distance between the sun and the earth = 8 light minutes
- The distance between Alpha Centauri and the earth = 4.3 light-years
Why are stars invisible during the daytime?
Stars are present in the sky during the day as well as at night time. However, during the daytime, the sunlight is so bright that it becomes difficult to locate stars in the sky.
Can Stars Change their positions?
If we observe a star or a group of stars for some hours their position appears to change. This is because of the motion of the earth. The earth keeps on revolving around the sun and hence changes its position with respect to the stars.
Why do Stars appear moving from east to west?
The rotation of the Earth takes place in a direction from west to east. To us, it appears as if the earth is still and the sky is moving from east to west direction. However, it is not true. Also, this is the same reason why the sun appears to rise from the east and set in the west.
The significance of the Pole Star
The pole star also called Polaris is situated close to the earth's axis of rotation. As a result, the position of the pole star appears to be fixed. This is unlike the other stars as their position keeps on changing with respect to the earth.