The sun, the moon, planets, stars and other bodies in the universe are called celestial bodies.
Some celestial bodies are very big and hot. They are made up of gases. They have their own heat and light. A celestial body which emits its own heat and light is called a star. The sun is an example of star. The light from a star appears to be flickering. This is called twinkling of star.
The sun is close to us, so it looks very big. All other stars are very far from us, so they look like tiny dots. You know that things appear smaller when they are away from us.
Stars are only visible during night. During daytime, we are unable to see stars because of sunlight.
In the night sky, you can see different patterns formed by groups of stars. Such a pattern of stars is called constellation. Ursa Major or Big Bear is one such constellation. Ursa Minor or Small Bear is a constellation which looks like Ursa Major but is smaller in size. Ursa Major is called Saptrishi in Hindi. There are seven main stars in this constellation. Both the constellations look like ladle and hence are called Big Dipper and Small Dipper. You can easily recognize them by taking help from an elder in your family. You can also locate the Pole Star with the help of these constellations.
Fig: Ursa Major
The Pole Star always appears in the north when seen from the northern hemisphere. Its position remains the same throughout the night and never changes. During ancient days, sailors and caravans used the Pole Star to find directions during night.
Some celestial bodies keep on moving around a star. They are called planets. A planet does not have its own light. The earth is a planet.
|Difference Between Star and Planet|
|Is huge in size.||Much smaller in size.|
|Emits its own light.||Planet does not have its own light.|
|Does not revolve around any other celestial body.||Revolves around a star.|
|Stars twinkle.||Planets do not twinkle.|
Some celestial bodies keep on moving around a planet. They are called satellites. The moon is the only satellite of the earth. Now-a-days, there are many man-made satellites in the sky. These satellites are used for different purposes.
Some Uses of Man-made Satellites
- For sending signals for television and telephone.
- For sending pictures of the earth.
- For sending data about climate. Scientists use this data to make weather predictions.
Light travels at the rate of 300,000 km per second. The sunlight takes about 8 minutes to travel between the sun and the earth.