Q. 1. Name a philosopher who believed that the earth was at the centre of the universe.
Ans. Aristotle—a Greek Philosopher.
Q. 2. What was meant by Geo-centric Theory ?
Ans. It meant that the moon, sun, planets and stars orbited around earth.
Q. 3. What is Helio-centric Solar System ?
Ans. The sun is the centre of solar system. All the planets, stars moved around the sun.
Q. 4. Name an Indian Scientist who believed in Helio-Centric System.
Q. 5. How many planets are there in Solar System ?
Q. 6. Name the inner planets.
Ans. Mercury, Venus, Earth and Mars.
Q. 7. Name the outer planets.
Ans. Jupiter, Saturn, Uranus and Neptune.
Q. 8. Name the unique planet where life exists.
Q. 9. Who forwarded the Nebula Hypothesis ?
Ans. German Philosopher Immanuel Kant and Laplace.
Q. 10. Who forwarded the collision Hypothesis ?
Ans. Sir James Jeans and Harold Jeffreys.
Q. 11. What was the shape of tongue of matter ejected from sun ?
Ans. Cigar shaped.
Q. 12. What do you mean by Supernova ?
Ans. A star million times brighter than the sun.
Q. 13. Which scientist of Russia modified the Nebular Hypothesis in 1950.
Ans. Otto Schmidt.
Q. 14. Which is the Hypothesis of Jeans and Jeffreys ?
Ans. Binary Hypothesis.
Q. 15. Which is the most popular theory regarding the origin of the Universe.
Ans. Big Bang Theory.
Q. 16. How much distance is travelled by light in a light year ?
Ans. 9.461 × 1012 km.
Q. 17. What do you mean by a ‘light year’ ?
Ans. A light year is a measure of distance and not of time. Light travels at a speed of 300,000 km/second. Considering this, the distance the light will travel in one year is taken to be one light year. This equals to 9.461 × 1012 km. The mean distance between the Sun and the Earth is 149,598,000 km. In terms of light years it is 8.311 minutes.
Q. 18. What is Solar System ? When was it formed ?
Ans. Our Solar System. Our Solar system consists of eight planets. The nebula from which our Solar system is supposed to have been formed started its collapse and core formation sometimes 5 to 5.6 billion years ago and the planets were formed by about 4.6 to 4.56 billion years ago. Our Solar system consists of the Sun, 8 planets, 173 moons, millions of smaller bodies like asteroids and comets and huge quantity of dust grains and gases.
Q. 19. How were oceans originated ?
Ans. Carbon dioxide in the atmosphere got dissolved in rainwater and the temperature further decreased causing more condensation and more rains. The rainwater falling on to the surface got collected in the depressions to give rise to oceans. The earth’s oceans were formed within 500 million years from the formation of the earth. This tells us that the oceans are as old as 400 million years.
Q. 20. Describe the different stages in the evolution of present day atmosphere.
Ans. There are three stages in the evolution of the present atmosphere. The first stage is marked by the loss of primordial atmosphere. In the second stage the hot interior of the earth contributed to the evolution of the atmosphere. Finally, the composition of atmosphere was modified by the living world through the process of photosynthesis.
Q. 21. (i) What is a Nebula ?
Ans. Nebula is a slowly rotating cloud of Gases. It contains hot gaseous matter of dust-gas clouds.
(ii) What are planetesimals ?
Ans. Due to collision of the sun and passing star, a filament of gaseous material was pulled away from the pre-existing sun. This filament (tongue-shaped) was broken into small chunks which went flying as cold bodies. These are called planetesimals.
(iii) Who first proposed Nebular Hypothesis ?
Ans. The Nebular Hypothesis was first proposed by German Philosopher Immanuel Kant in 1755.
(iv) What is a Protostar ?
Ans. The Nebula of hot gaseous cloud exploded to form a Supernova. Its denser portions collapsed under their own gravity. The dense core became larger and hotter. It is called Protostar It finally became the infant sun.
Q. 22. Describe the modification proposed in Nebular Hypothesis by Otto Schmidt.
Ans. In 1950 Otto Schmidt in Russia and Carl Weizascar in Germany somewhat revised the ‘nebular hypothesis’, though differing in details. They considered that the Sun was surrounded by solar nebula containing mostly the hydrogen and helium alongwith what may be termed dust. The friction and collision of particles led to formation of a disc shaped cloud and the planets were formed through the process of accretion.
Q. 23. Describe the process of Star Formation.
Ans. The Star Formation. The distribution of matter and energy was not even in the early Universe. These initial density differences gave rise to difference in gravitational forces and it caused the matter to get drawn together. These formed the basis for development of galaxies. The galaxies contain a large number of
stars. They spread over vast distances, to be measured in thousands of light-years. These range in size with diameters ranging from 80,000 to 150,000 light years.
A galaxy starts to form by accumulation of hydrogen gas in a very large cloud called nebula. Eventually growing nebula develops localised clumps of gas, which continue to grow into even denser gaseous bodies giving rise to formation of stars. The formation of stars is believed to have taken place some time 5 to 6 billion years ago.
Q. 24. Compare the inner planets and outer planets.
Ans. Of the eight planets Mercury, Venus, Earth and Mars are called as inner planets as they lie between the Sun and the belt of asteroids called the asteroid belt. The other four plants, lining up after the asteroid belt are Jupiter, Saturn, Uranus and Neptune are called outer planets. Alternatively the first four are called ‘Terrestrial’, meaning Earth like, as they are made up of rock and metals and have relatively high densities. The rest four are called Jovian or Gas Giant planets. Jovian means Jupiter like. Most of them are much larger than the terrestrial planets and have a thick atmosphere mostly of helium and hydrogen. All the planets were formed in the same period, some time about 4.6 billion years ago.
Q. 25. Describe a comparative analysis of planets as regards distance from the sun, density, radius and satellites.