Stars and the Solar System

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1. Match the following:

a. iv 

b. v 

c. ii 

d. i 

e. iii

2. Name the following:

a. Uranus 

b. Mars 

c. Venus 

d. Mercury 

e. Neptune

3. Fill in the blanks:

a. Asteroid belt 

b. Nucleus 

c. Crater 

d. Full moon 

e. Sputnik-1

Assessment Zone

A. Choose the correct answer.

 1. c 

2. b 

3. a 

4. c

5. b 

6. a 

7. b

B. Fill in the blanks.

 1. Star

 2. Terrestrial planets

 3. Halley’s

4. Phobos, Deimos 

5. Venus

C. State True or false.

1. False 

2. False 

3. True

4. False 

5. False 

6. True

D. Answer in the word.

1. Cassiopeia 

2. Pleiades 

3. Moon

4. Mars 

5. Uranus

E. Match the following:

1. e 

2. c 

3. b 

4. a 

5. d

F. Answer the following questions in brief.

 1. An astronomical unit is the average distance between the Earth and the Sun. It is

denoted by ‘au’. A light year is the distance travelled by light in one year. It is denoted

by ‘ly’.

 One light year is almost six trillion miles and an astronomical unit is the average

distance between the Earth and the Sun. So the distance to the Sun is by definition one

au.

One light-year is 63,241.1 astronomical units.

2. Stars shine during the day, but we cannot see them because of the glare of sunlight.

When the Sun is up, the blue colour in sunlight gets scattered all over the atmosphere,

turning the sky the familiar bright blue colour.

3. A large collection of stars and celestial bodies such as planets, moons, asteroids and

comets bound together by gravitational attraction is called a galaxy.

4. A group of stars that forms a pattern in the sky when viewed from the Earth is called a

constellation.

5. To enable life, this most special of attributes, planet Earth has many ideal features. It

is unique among planets in our solar system for having water in its liquid form at the

surface, in an amount conducive to evolve life.

6. It must be meteorite, as a small piece of rock that gets destroyed completely in the

Earth’s atmosphere and does not reach the Earth’s surface.

G. Answer the following questions in detail.

  1. A light year is the distance travelled by light in one year. It is denoted by ‘ly’.

1 ly = 9.461 × 1012 km

Therefore; 150 x 106

 km = (1/9.461 × 1012) × 150 × 106 ly

 = 1.58 × 10 –11 ly

2. a. Planet and star

Star Planet

Stars are the astronomical objects that

emit their own light, produced due to

thermonuclear fusion, occurring at its

core.

Planets refer to the celestial object that

has a fixed path (orbit), in which it moves

around the star.

They have their own light. They do not have their own light.

Their position remains unchanged. They change position.

There is only one star in the solar system. There are eight planets in our solar

system.

Matter present are hydrogen, helium and

other light elements in gaseous form.

Matter present in solid, liquid or gases

form.

b. Moon and asteroid

Moon Asteroid

Moons orbit planets. Most of them are

thought to have formed along with those

planets or to have resulted from collision.

Most of the asteroids are found between

the orbits of Mars and Jupiter. This region

is called the asteroid belt.

The Moon is a satellite. It orbits a planet. The asteroids orbit the Sun directly.

c. Comet and meteorite

 Comets are also composed of material left over from the formation of our solar system. It

is a ball of ice, dust and gases that orbits the Sun. However, asteroids formed toward the

inner regions of our solar system where temperatures were hotter and thus only rock or

metal could remain solid without melting. Comets formed at farther distances from the

Sun, beyond what we call the frost or snow line and past the orbits of Mars and Jupiter,

where temperatures were low enough for water to freeze.

 A meteoroid is a chunk of rock, moving in space, of a size considerably smaller than

an asteroid. As the meteoroids come close to the Earth, they get attracted towards the

Earth’s surface because of its gravitational pull. They are usually destroyed completely

by friction and heat when they pass through the Earth’s atmosphere. They appear as a

streak of light in the sky. Meteorite is a piece of meteoroid that makes it to the surface

of the Earth.

d. Artificial and natural satellites

Natural Satellites Artificial Satellites

The natural satellites are celestial bodies

that orbit a planet or any other celestial

body.

The artificial satellite is a device placed in

orbit around the Earth, moon, or another

planet.

These are formed by nature. The artificial satellites are man made.

The natural satellites are objects that

orbit the Earth such as the Moon.

The first artificial satellite was Sputnik

I. The artificial satellites are man-made

objects that propel through the Earth’s

atmosphere in order to orbit around the

Earth.

Natural Satellites Artificial Satellites

Natural satellites like planets are opaque

bodies with no light of their own. They

also receive heat and light from Sun.

The electrical power required by satellite

is provided by panels of solar cells and

small nuclear reactors. These are used

and controlled by the astronomers.

The natural satellite is made up of natural

material, rock, minerals, water, dust, etc.

The artificial satellite is made out of metal

and electronics material.

The natural satellites are normally

massive enough to stay in orbit under the

influence of gravity indefinitely.

They experience decay of orbit as the

Earth’s gravity slowly reasserts its hold

on them until they eventually slow down

and crash back to Earth.

3. Using the formula, time = distance/ speed

Distance = 9 ly = 9 × 9.461 × 1012

 Speed = 22 km/s

Therefore; time = 9 × 9.461 × 1012/ 22

= 4 × 1012 sec

= 1.1 × 109

 hrs

4. Different shapes of Moon are visible on different days. These various shapes of the Moon

are known as the phases of the Moon.

 For diagram, please refer Fig. 17.24 (Phases of the Moon) on page no. 259

5. A group of stars that forms a pattern in the sky when viewed from the Earth is called a

constellation.

Ursa Major is the third largest constellation. It is also known as the Great Bear, the Big

Dipper or the Plough. Out of many stars, it forms a group of seven bright stars which

resembles the shape of a big dipper. It is visible in the northern hemisphere almost

throughout the year. It is well-known as the Vrihat Saptarishi Mandal.

    Ursa Minor is known as the Little Bear or Little Dipper. It also consists of a group of

seven stars that form the shape of little dipper with Pole star at the end of the dipper’s

handle. However, it is not easy to spot little dipper as, except Pole star, rest of the stars

are not so bright. It is commonly known as Laghu Saptarishi Mandal.

6. A celestial object that revolves around a planet is called the natural satellite. It is also

known as the moon of a planet. All planets except Mercury and Venus in our solar

system have moons.

  • Natural satellites help us to reveal secrets of the space. They are subject of space

studies.

  • Natural satellites help to design artificial satellites.

  7. Our solar system consists of an average star we call the Sun, the planets Mercury,

Venus, Earth, Mars, Jupiter, Saturn, Uranus, Neptune, and Pluto. It includes:

the satellites of the planets, numerous comets, asteroids, and meteoroids and the

interplanetary medium.

 Planets: Our solar system has eight planets—Mercury, Venus, Earth, Mars, Jupiter,

Saturn, Uranus and Neptune. They are the heavenly objects that orbit the Sun. They do

not have their own light. They reflect the light coming from the Sun.

 Asteroids: Asteroids are large and rocky objects having irregular shape that revolve

around the Sun. Most of the asteroids are found between the orbits of Mars and Jupiter.

This region is called the asteroid belt.

 Comets: A comet is a ball of ice, dust and gases that orbits the Sun. It revolves in a

specific orbit around the Sun. Their orbits are so elongated that some comets may take

thousands of years to complete one revolution.

 Meteoroids, meteors and meteorites: A meteoroid is a chunk of rock, moving in space, of

a size considerably smaller than an asteroid. A meteoroid that is destroyed completely

in the Earth’s atmosphere and does not reach the ground is called a meteor. A piece of

meteoroid that makes it to the surface of the Earth is called a meteorite. When it hits

the surface of the Earth, it results in a bowl-shaped depression known as a crater.

 Satellites: An object that orbits a planet is called a satellite. Satellites can be natural or

artificial, depending upon the objects that are orbiting around the planets.