General Science Solutions Solutions for Class 6 Science Chapter 16 - The Universe

Answer:

(a) Birth place of stars: Nebula
(b) Biggest planet in the solar system: Jupiter
(c) The galaxy which is our neighbour: Andromeda
(d) Brightest planet in the solar system: Venus
(e) Planet with largest number of satellites: Jupiter
(f) Planets without a single satellite: Mercury and Venus
(g) Planet with a rotation different from other planets: Venus and Uranus
(h) A celestial body that carries a tail along: Comets

Answer:

(a) The group of galaxies of which our Milky Way is a part is called 'Local Group'.
(b) Comets are made of ice and dust particles.
(c) The planet Uranus appears as if it is rolling along its orbit.
(d) Jupiter is a stormy planet.
(e) The Pole Star is the best example of a variable type of star.

Answer:

(a) No, the statement is incorrect. Mercury is the planet closest to the Sun.

(b) No, the statement is incorrect. Jupiter is called a stormy planet.

(c) Yes, Jupiter is the biggest planet.

Answer:

(a) The special characteristic of planet Mars is that it is red in colour. This is due to the presence of iron in its soil.

(b) Various types of galaxies which are identified according to their shapes are:

• Spiral galaxy: These are the spiral structures that extend from the centre into the disc. It consists of stars, gas and dust in a bulge at the centre and in the extended spiral arms.
• Elliptical galaxy: These galaxies have nearly ellipsoidal shape which consists of stars, gas and dust.
• Irregular galaxies: These galaxies don’t have a distinct regular shape.
• Barred spiral galaxies: These are spiral galaxies with a central bar-shaped structure composed of stars.

(c) A galaxy includes stars, cluster of stars, nebulae, clouds of gases and dusts, dead stars, newly born stars etc.

(d) The different types of stars in the universe are stated below:
Sun-like Stars: These are particularly similar to the Sun in size but there is a lot of variation in terms of temperature. Examples are Alpha Centurai, Tau Ceti etc.
Red Giants: These stars do not have as hot outer layer as that of the Sun with temperature ranging from 3000 ^oC to 4000 ^oC but they have a very high luminance than the Sun. They are red in color and their diameter is 10 to 100 times that of the Sun.
Super Nova: They are larger and even brighter as compared to the red giant stars and even the Sun. They are also considered as the primary source of heavy elements in the universe.
Binary or Twin Stars: A pair of two stars in which one revolves around the other or they both revolve around a common centre is known as binary or twin stars. 
Variable Stars: These stars have a variable shape and brightness i.e it keeps on changing whenever they expand or contract. Their brightness decreases when they expand and increases when they contract. Example is Pole Star.

(e) Comets are the solar system bodies that are usually spherical in shape and develop tail when they come near the Sun. Comets become visible when they are close to the Sun and the Earth.

Comets can be categorized into two groups depending on how long they take to complete one revolution around the sun. These are:

• Long Period Comets: These comets complete one revolution around the Sun in 200 and more years. Great Comet of 1843 is one of the examples of this type.
• Short Period Comets: These comets complete one revolution around the Sun in years less than 200. One of the examples is Halley's comet that takes 76 years to complete the revolution. It last appeared in 1985.

(f) Meteors: These are rocky pieces originating from the asteroid belt and enter the Earth’s atmosphere as a result of its gravitational pull. On entering the Earth’s atmosphere, they acquire very high speeds. These high speeds of meteors cause friction with the Earth’s atmosphere and thus the meteors heat up and evaporate completely. Meteors are also known as shooting stars.

Meteorites: These are the unburnt part of meteors which fall to the surface of Earth on ocassions when the meteors do not burn completely in the atmosphere itself.

(g) Following are the characteristics of planet Neptune:

• A season on this planet lasts for about 41 years.
• Wind blows with extremely high speed on this planet.

Answer: