Science Chapter 17 Stars And Solar System

C.

A constellation

A.

Sirius

C.

the shadow of the Earth covers only a part of the moon's surface.

Neptune

Mars

Constellation

satellite

meteors

mars

jupiter

In western sky.

Jupiter.

The stars forming a group that has a recognisable shape is called a constellation.

E.g. Orion and great bear

Meteors and Asteroids are also members of Solar system.

Pole star is situated at the end of the Ursa Major. If an imaginary straight line starting from the last two stars is extended towards the north direction, it will lead to the Pole Star.
Pole star is not too bright.

Stars in the sky appear to be moving because of the rotation of earth on its axis. Earth moves from west to east. Therefore, it appears as if stars are rising in the west and as day dawns they set in the west.

So, stars are relatively in motion with respect to the roation of Earth. 

Stars are away from the earth millions of kilometres away. It is not convenient to express such a large distance in the units of km.

So, the distance of stars from the earth is expressed in light years. One light year is the amount of time taken by the light to travel in one year. Eight light years means, time taken by light to travel in eight years. 

No, the given sketch is not correct.The position of Mars in the given solar system is incorrect. 

 The following figure given below is correct. 

Mercury.

Mars.

Alpha centuari.

Saturn.

Sun.

Venus.

Mars.

Mercury.

Saturn.

The inner planets are Mercury, Venus, Earth and Mars.

Outer planets are Jupiter, Saturn, Uranus and Neptune.

INSAT, IRS, Kalpana 1 are few artificial satellites.

Mercury and Venus have no satellite of its own.

Earth.

Mercury.

The Sun is classified as a star as it emits it's own light. Sun has it's own source of energy and hence emits heat and light continuously.

The gravitational attraction between the Sun and the planets keeps them revolving around it.

Pole star is situated on the axis of the earth. Hence, it does not appear to be moving relative to the rotation of the Earth. 

Milky way (Akash Ganga) is the galaxy that contains our Solar system. 

Moon.

Moon has no atmosphere. Therefore, the propagation of signals required for communication will not take place at the surface of the moon. 

Asteroids.

The ancient people found the night sky to be very useful to find the direction. The position of pole star remained fixed in the north sky and it indicated North direction. As the stars change their position with time, it has been possible to find the time with relative position of stars. 

The earth rotates on its axis from west to east, therefore, the stars appear to move in opposite direction, i.e. east to west. But pole star lies on the axis of rotation of earth, which is fixed. Hence, pole star appears to be fixed in the sky.

Pole star lies in the northern part of the sky and enables us to find the North direction.

When meteors enters the earth's atmosphere, its speed is very high. The friction due to the Earth's atmosphere heats it up. On heating up, it emits light and glows producing a bright streak of light. Since they get evaporated quickly, the bright streaks lasts only for a short duration of time.

Planet Mercury being closest to the Sun has extremely high temperature on it making the survival of life impossible. Moreover, Mercury does not have water on its surface and there is no carbon dioxide, hydrogen, nitrogen and oxygen in its atmosphere. Also, there is no protective blanket around the Mercury planet to prevent harmful radiations from reaching its surface. 

Mercury and Venus are the two planets that can be seen as morning and evening star in the sky.

Mercury being the closest to the Sun is hidden in the glare of the sun and is rarely visible. However, it can be observed just before the sunrise or after the sunset near the horizon.

Venus appears in the eastern sky before sunrise and appears in the western sky after the sunset. 

Due to their visibilty before sunrise and after sunset, they are called evening and morning star. Also, Mercury and Venus lie inside the orbit of the earth.

Venus is close to the Sun. So, this planet has extremely high temperature. The temperature of Venus further increases because of increase in greenhouse effect. Hence, the planet does not support the survival of even primitive lifeforms. 

Sun shift towards South from 21st June and from 22nd December Sun starts shifting towards North.

Moon is a natural satellite of the earth. But, it cannot be used as a communication satellite because of the following reasons:

(i) It is very far away from earth.

(ii) Its orbital time period is 27.3 days, which is too long.

(iii) It has neither equitorial orbit nor polar orbit which makes a satellite useful for different purposes.

The number of meteorites striking the moon's surface is large but very few of them reaches the Earth's surface. On entering the Earth's atmosphere, most of the meteorites burn up completely due to the heat produced by friction between falling meteorite and air. Hence, less meteorites strikes the Earth's surface as compared to the moon. 

Natural satellites

1. They are far away from planets.
2. They are comparatively larger in size and are present naturally. 
3. Natural satellites do not have light of their own. They receive light from the Sun.

Artificial satellites

1. These satellites are man made and are sent from earth with specific requirements.
2. Their distance, size and mass are lesser than the natural satellite. 
3. The electrical power required by artificial satellites is provided by panels of solar cells and small nuclear reactors. 

The Solar system consists of the Sun and the celestial bodies which revolve around the Sun. Added to that it consists of a large number of bodies such as planets, comets, asteroids and meteors. The sun is the centre of the solar system and all the planets revolve around the sun in elliptical paths called orbits. 

The planets situated between the sun and the earth are Mercury and Venus.

Sun is located closer to the earth as compared to stars. Stars are million times farther away than the sun. Therefore, stars appear to us like points and Sun appears bigger.

Moon does not produce light of it's own. It reflects light of the sun falling on it. On new moon day, moon is between the Sun and the Earth and no reflected light from it reaches the earth. We cannot see moon on that day. The visibility of moon increases every day till fifteenth day from the new moon day, the full phase of the moon is visible.



So, the waxing and waning of moon periodically, as it revolves around the earth is called phases of moon.

(a) Constellations.

(b) Ursa major, Great bear.

(c) No. Constellations are made up from other stars. So, it is not a part of our solar system.They are a part of our galaxy.

(d) Seven to eight bright stars are usually observed in a constellation.

(e) Pole Star can be located in the sky.

(a) The stars appear to move in the sky from east to west direction.

(b) Stars move in a direction opposite to the rotation of Earth. Rotation of Earth is from west ro east direction on it's axis. Therefore, stars move from east to west. 

A : Cassiopeia has 5 bright stars.

B : Ursa Major has 7 bright stars.

C : Orion has 8 major bright stars.

D : Leo Major usually has 9 bright stars.

Lifeforms cannot be supported on Venus due to the following reasons:

(i) Venus does not have water.

(ii) Venus does not have the right temperature range. It is too hot to support even the primitive forms of life. Venus lies very close to the Sun as compared to the Earth.

(iii) Venus does not have a protective blanket around it to prevent harmful radiations from entering its atmosphere.

Asteroids are very small pieces of rocks and metal which revolve around the Sun mainly between the orbits of Mars and Jupiter. 
Asteroids were formed early in the history of the Solar system around 4.5 billion years ago.

The conditions which make Earth a living planet is as given below: 

(i) Earth has elements like carbon, hydrogen, oxygen, and nitrogen which are needed for the synthesis of molecules required for the origin of life. It has also sufficient oxygen gas in its atmosphere.

(ii) Earth has the right temperature range for the life to originate and flourish on it. It is neither too cold nor too hot.

(iii) Earth has lot of water on its surface.

(iv) Earth has a protective blanket of ‘ozone gas’ around it, which prevents harmful radiations from entering its atmosphere.

Pole star is the only star in the sky which appears stationary to an observer on Earth. Pole star is also called Polaris or Dhruvtara in India. 

Pole star lies along the direction of the axis of rotation of the earth. Since it lies on the axis of rotation of the Earth, it appears stationary for an observer on Earth.  

Meteors are the heavenly bodies from the sky which we see as a bright streak of light that flashes for a moment across the night sky. Meteors are the dust particles left behind by comets or pieces of asteroids which have collided. 

When a meteor enters into earth's atmosphere with a high speed, it burns due to heat produced by the friction of atmosphere and becomes visible to us in the form of a bright streak of light shooting down the nighty sky. Most of the meteors are small rocky particles and burn up completely due to the extreme heat on entering earth's atmosphere but some are big and do not burn completely.

A meteor which does not burn up completely on entering earth's atmosphere and lands on earth in the form of a stone or rock is called a meteorite. 

The apparent motion of stars in the sky is due to motion of earth around its axis. The earth rotates on its axis from west to east, due to which the stars appear to move in the opposite direction from east to west.
Pole star appears to be stationary because it lies on the axis of rotation of earth, which is fixed in space and does not change with time. 

Earth

Mercury

Pole Star

B.

Venus

A.

Neptune

A.

Constellation

D.

Great bear

D.

East to West

B.

constellation

B.

constellation

B.

76 years

A.

Shooting stars

D.

Cassiopeia

A.

Meteorite

(a) The diagram of Solar system is given by, 





(b) There are eight planets in solar system named: Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, Neptune.