Topic outline

    • Stars and Solar System

      Q90. What are some unique characteristics of Saturn?

      Ans. Saturn appears yellowish in colour. It has a well-developed system of rings around it. These rings are not visible with the naked eye. We can observe them with a small telescope. It also has a large number of satellites. One interesting thing about Saturn is that it is the least dense among all the planets. Its density is less than that of water.


      Q91. Draw a diagram of Cassiopeia constellation to show the position of main stars in it.


      Image from NCERT

      Q92. Draw a diagram to show the position of main stars in Leo Major constellation.


       Image from NCERT


      Q93. How is the surface of the moon?

      Ans. The moon is a fascinating object for poets and story-tellers. But when astronauts landed on the moon, they found that the moon’s surface is dusty and barren. There are many craters of different sizes. It also has a large number of steep and high mountains. Some of these are as high as the highest mountains on the Earth.


      Q94. What factors make life possible on Earth?

      Ans. The Earth is the only planet in the solar system on which life is known to exist. Some special environmental conditions are responsible for the existence and continuation of life on the Earth. These include just the right distance from the Sun, so that it has the right temperature range, the presence of water and suitable atmosphere and a blanket of ozone.

      Q95. What is meant by the phases of the Moon? Why phases of the moon occur?
      Why does the moon change its shape every day?

      Ans. The various shapes of the bright part of the moon as seen during a month are called phases of the moon. The moon does not produce its own light, whereas the Sun and other stars do. We see the moon because the sunlight falling on it gets reflected towards us. We, therefore, see only that part of the moon, from which the light of the Sun is reflected towards us. This is how phases of the moon occur.


      Q96. Why is it difficult to observe the planet Mercury?

      Ans. The planet mercury is nearest to the Sun. It is the smallest planet of our solar system. Because Mercury is very close to the Sun, it is very difficult to observe it, as most of the time it is hidden in the glare of the Sun. However, it can be observed just before sunrise or just after sunset, near the horizon. So it is visible only at places where trees or buildings do not obstruct the view of the horizon.


      Q97. The radius of Jupiter is 11 times the radius of the Earth. Calculate the ratio of the volumes of Jupiter and the Earth. How many Earths can Jupiter accommodate?


      Q98. Why is the distance between stars expressed in light years? What do you understand by the statement that a star is eight light years away from the Earth?

      Ans. The Sun is nearly 150,000,000 kilometres (150 million km) away from the Earth. We cannot read this distance in kilometres conveniently. Some stars are even further away. Thus, such large distances are expressed in another unit known as light year. It means the distance between the star and the Earth is equal to the distance travelled by light in eight years.

      1 light year= 9.46 × 1012 Km. 

      Therefore, the star is located 8 × 9.46 × 1012 Km = 75.68 × 1012 Km away from the Earth.

    • Download to practice offline.