The Earth in the Solar System Question Answers: NCERT Class 6 Social Science - The Earth Our Habitat

(a)

(b) The sun, eight planets, satellite and some celestial bodies (asteroids and meteoroids) are bounded together by gravitational energy in a pattern to form solar system. There are four inner planets and four outer planets in the solar system. Inner planets are closer to the sun and are small. They are Mercury, Venus, Earth and Mars. They are separated from the outer planets by the Asteroid belt. The outer planets are far away from sun and huge in size. They are Jupiter, Saturn, Uranus and Neptune. The smallest planet in our solar system Is Mercury and the largest one is Jupiter. Our solar system comes in Milky Way galaxy.

(c) There are 8 planets. The planets according to their distance from the sun are as follows:

1. Mercury: It is the closest planet to the sun and as well as the smallest planet. Its distance from the sun is about 57.9 million km.
2. Venus: It is the second closest planet to the sun. Its distance from the sun is about 108 million km away.
3. Earth: It is the third closest planet to the sun. Its distance from the sun is about 150 million km away.
4. Mars: It is the fourth closest planet to the sun. Its distance from the sun is about 228 million km away.
5. Jupiter: It is the fifth closest planet to the sun. Its distance from the sun is about 778.3 million km away.
6. Saturn: It is the third farthest planet from the sun. Its distance from the sun is about 1429.4 million km.
7. Uranus: It is the second farthest planet from the sun. Its distance from the sun is about 2871 million km.
8. Neptune: It is the farthest planet from the sun. Its distance from the sun is about 4504.3 million km away.

(d) Earth is called a unique planet because of following reasons:
1. It is the only planet where life exists. The air contains some life supporting gases like O 2 .
2. The temperature of the earth is neither too hot nor too cold. Conditions favorable to support life are probably found only on earth.
3. There is water present in the earth which is very essential for the survival. There are so many geographical features on Earth like volcanoes, islands, mountains, oceans, deserts, grasslands, forests etc.
4. Abundance of water makes the Earth which is also known as ‘blue planet’. The Earth is also the densest planet in the solar system.

(e) We only see one side of the moon because the moon takes 27 days to complete one orbit around the earth. It takes some time to spin once on its axis. The side of moon that faces the Earth is called ‘near side’ and the opposite one is known as ‘far side’.

(f) The vast expanse of space or the largest unit in which life exists is called Universe. It is infinite in volume. The three most common elements in universe are Hydrogen (H 2 ), Helium (He) and Oxygen (O 2 ). The universe is so dark that it is invisible and is also called as ‘dark matter’.

(a) Venus
Venus is called Earth’s Twin because it is similar to the earth in shape and size. Venus is also called sister of Earth. Both Earth and Venus are rocky planets. They effectively have same density and are nearly having same mass. They both have significant atmospheres, surrounding their surfaces. Venus’s radius is only a few hundred kilometers smaller than Earth.

(b) Earth
Earth is the third nearest planet to the sun and is about 150 million km away from the sun. Revolution of 365 days is taken by the earth and 24 hours to rotate around sun on its axis. Earth’s gravity is interconnected with other bodies in space, especially from the sun and the moon. The exact distance between Earth and the sun varies with its position in its elliptical orbit.

(c) Elliptical path
All the planets go around the sun in an elliptical path or an orbit. Elliptical shape does not seems to be a perfect circle but seems like an oval shape.

(d) North
Pole star is also known as North Star. The North Star always indicates the North direction. In ancient times, people used to determine directions during night with the help of stars. The position of the pole star always remains same in the night sky. We can locate the position of pole star with the help of Saptarishi. If an imaginary line is drawn by joining the pointer star and extended further, it will point to the pole star.

(e) Mars and Jupiter
Asteroids are numerous tiny bodies which also move around the sun. Asteroid forms a belt between the orbits of Mars and Jupiter which separates inner and outer planets. The belt formed by asteroids is known as asteroid belt. The largest asteroid is Ceres and is the first asteroid to be spotted. The brightest asteroid is Vesta and is the only asteroid that can be seen with the naked eyes. The Trojans are two small groups of asteroids that circle the sun on the same orbit as Jupiter.

a) Star, Constellation
The pattern formed by the stars in the night sky is called constellation. The star in each constellation are named after letters in the Greek alphabet. The brightest star in each constellation is known as Alpha, the next is Beta and so on. So, Alpha Pegasi is the brightest star in Pegasus, the flying horse. Without constellations, it would be hard to locate the stars in the night sky, but there is no real link between the stars in a constellation; they are completely imaginary patterns. The Big Dipper, also known as Great Bear or Ursa Major, is one of the best known constellations in the Northern sky. It points towards Pole star, indicating north. Example: The Great Bear, the Water Snake (Hydra), the Little Bear (Ursa Minor).

b) Galaxy
The gigantic collection of stars, known as galaxy. It is huge system of billions of stars and clouds of dust & gases. The galaxy in which we live is Milky Way, it gets its name because we see it as a milky white band across the night sky. Galaxy is just one of many millions of similar giant groups of stars, scattered throughout the Universe. There are three types of galaxies:

1. Spiral galaxy: It consists of flat disk with a bulging center and surrounding spiral arms. When a spiral galaxy has a bright line (or bar) running through it, then it is called ‘barred spiral galaxy’.
2. Elliptical galaxy: They are oval shaped, but stretch longer along one axis. They may be nearly circular and are so elongated that they take on a cigar like appearance.
3. Irregular galaxy: They have little or no definite structure because they are within the gravitational influence of other galaxies closed by.

c) Moon                                                                                                                                                                                                                                        Moon is the closest celestial to our earth. It is the only natural satellite of the Earth. Moon is about 3, 84,400 km away from the Earth. The Moon takes 27 days to complete one orbit around the Earth. It takes exact time to spin or rotate in its axis. Moon is the fifth largest natural satellite in the solar system and is second densest satellite after Io, a satellite of Jupiter. Its mass is approximately one eightieth that of Earth. Moon is close to Earth so it looks much larger than the stars.

d) Earth
Earth is the 3 rd nearest planet to the sun. 1 st nearest planet is Mercury and 2 nd is Venus, 3 rd is Earth, 4 th is Mars, 5 th is Jupiter, 6 th is Saturn, 7 th Uranus and then the farthest planet Neptune.

e) Heat, light
Planets do not have their own heat and light. They receive heat and light from the sun. As they do not have their own heat and light, so that is the reason they do not twinkle like the stars do. They don’t twinkle because planets appear big enough so that the refraction of light is not noticeable and the lights from the planet arrives as a steadily stream because of its closeness, not with speedy, intermittent break.