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Correct option is C) 3,474

Correct option is C) Seasons

ISRO also known as Indian Space Research Organisation is the agency responsible for the development of space science programs in India.

Moon is the natural satellite of the Earth. Aryabhatta was the first Indian artificial satellite of the Earth.

Earth is the only planet of the Solar System having life on it. The special environment conditions are responsible for the existence and the continuation of life on the Earth. These conditions include the right distance from the Sun, so it has the right temperature, the presence of water, suitable atmosphere and a blanket of ozone.

Any celestial body revolving around another celestial body is called its satellite. The Earth is the satellite of the Sun because it revolves around the Sun. The bodies revolving around the planets are considered as satellites of the planet. Moon is the natural satellite of Earth.

(a) The Earth rotates on its axis taking approximately 24 hours to complete one rotation. Rotation of Earth causes the day night cycle which also creates a corresponding cycle of temperature and humidity.

(b) The plane in which the Earth revolves round the Sun is called the orbital plane of the Earth. The axis of rotation of the Earth is not perpendicular to the plane of its orbit. These two planes are inclined to each other at an angle of 23.5° This tilt is responsible for the change of seasons on the Earth.

Meteorites are the large meteors which can reach the Earth before they evaporate completely. Meteorites help scientists in investigating the nature of the material from which the solar system was formed.

Stars are celestial bodies that emit light of their own. Our sun is also a star. The stars appear to move from east to west. A star which rises in the east in the evening, sets in the west in the early morning. Meteors are commonly known as shooting stars. Meteor is seen as a bright streak of light coming down the night sky. It is usually a small object that occasionally enters the Earth’s atmosphere with very high speed.

i. horizon

ii. meridian

iii. nine

iv. apparent

Moon and the stars are the celestial objects which we can see easily in the night sky.

The pole star is the star which remains fixed at the same place in the sky in the North.

The star nearest to the earth is the Sun. Hence, it appears quite big and bright. There are billions of stars in our galaxy called the Milky Way and Mandakini which are greater or lower in mass, size and temperature than the Sun. Hence, the Sun is called an ordinary star.

Although stars appear stable for quite a long period of time, their properties do change, though very slowly. A change in the properties of a star, leading to its passing through different stages, is called evolution of the star. Burning of the fuel at the centre of the star and a gradual decrease in its amount is the main reason of evolution of a star.

In olden days people felt that earth is flat because it looks flat. However they had a doubt, if it is flat how does the water in ocean remain there, Why does it not spell out of the earth ? To get clarity they assumed fencing around flat earth. After that,

1. they assumed shape of earth is round by observing the shadow of earth in lunar eclipse. In every eclipse they found the shape of the earth is in round even though there is a chance of getting linear, elliptical shadows by a circular object. 

2. some sailors who started their journey in ocean, reached the same place after travelling large distance in one direction only. 

3. observing ships approaching the port also helped to change their opinion about the shape of the earth, that is, usually they see smoke of the ship first and then top of the ship after that the whole ship.

4. observations about the movement of stars. Different stars visible from different places on the earth also helped to think about the shape of the earth. 

5. in 1969 when man landed on the moon and observed the earth’s shape from the moon and it is spherical.

1. Take a stick which is a little over a meter long and fix vertically in the ground. 

2. Make your first observation at nine in the morning. Make a mark with a nail or peg at the point where the tip of the shadow falls on the ground. Measure the length of the shadow. 

3. Then make similar observations for every half an hour throughout the day till four in the evening. 

4. Use a clock to fix the time for making your observations. 

5. Enter the measurements of the length of the shadow and the time of measurement in a table making two columns, one for time and other for length of shadow. 

6. Find the time when the shortest show occurs. 

7. That gives the local noon time at that place.

1. Stars having initial mass less than 8 times the mass of the Sun ultimately become white dwarfs. 

2. Stars having initial mass between i 8 and 25 times the mass of the Sun ultimately become neutron stars. 

3. Stars having initial mass larger than 25 times the mass of the Sun ultimately turn into black holes.

People from olden days thought that earth is located in the centre of the universe with sun, moon and stars moving around it. They also thought that sun, moon and stars are located on transparent concentric spheres surrounding the earth, because they are not falling down.

The three spheres are rotating on their axis from east to west that is why sun, moon and stars appear to revolve from east to west around the earth. They also assumed that the shpere on which sun is located rotates east to west and oscillate from south to north that is why Uttarayanam and Dakshinayanam are happening.

Because of the uneven movement of some stars (actually they are planets) which they observed, it is very difficult to explain model of universe which required so many transparent spheres around earth. Nicholas Copernicus suggested that sun is at the centre of universe and all other celestial objects 

A black hole is the end stage of a quite big star, where due to the extremely high gravitational force, nothing, not even light, comes out.

Planets are the members of the Solar System. They look like stars but they do not have light of their own. They reflect the sunlight that fall on them. They keep changing their positions with respect to the stars. A planet revolves around the Sun in a definite path. This path is called an orbit. The time taken by a planet to complete one revolution is called its period of revolution. As the distance of the planet increases from the Sun, the period of revolution increases. A planet also rotates on its axis besides revolving around the Sun. The time taken by the planet to complete one rotation is called its period of rotation. Some planets have moons or satellites revolving around them.

IUCAA which is present in PUNE carries out fundamental research in astronomy.

Mercury is the smallest planet of the Solar system. It is nearest to the Sun.

The Sun and the celestial bodies which revolve around it form the Solar System. The Gravitational force keeps the members of the Solar System bound to the Sun. The Earth is a planet. It is the member of the Solar system. The eight planets in their order of their increasing distance from the Sun are: Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus and Neptune.

The Sun is the nearest star which is continuously emitting huge amount of heat and light. The Sun is the source of almost all the energy on the Earth.

The Sun and the celestial bodies which revolve around it form the solar system. It consists of large number of bodies such as planets, comets, asteroids and meteors. The Gravitational force keeps the members of the Solar System bound to the Sun.

When seen from earth, stars appear to move from east to west.

When a star having initial mass larger than 25 times the mass of the Sun reaches its end stage, its gravitational force and density increase exponentially. All nearby objects get attracted towards the star and nothing can come out of it, not even light. All incident light is absorbed by the star. We can probably see a very minute black hole at its place. Hence, the name is given as black hole.

There are billions of stars in the galaxy called the Milky Way and Mandakini. I am one of the small stars called the Sun. I have my own family called the solar system. There are planets, satellites, asteroids, comets and meteors in my family. My mass is 2 × 1030 kg which is about 3.3 lakh times that of the earth. With a radius of 695700 km, my size is about 100 times that of the earth. My surface temperature is about 5800 K while it is 1.5 × 107 K at the centre.

72 % of my mass consists of hydrogen while 26 % consists of helium. Rest 2 % is made up of elements heavier than helium. I am about 4.5 billion years old and the scientists on the earth have concluded that not much change has taken place in my properties during this period. According to the scientists, in the end stage of my life, I will turn into a red giant star. Thereafter, I will first explode and then contract to become as small as the earth. I will appear small as well as white and hence, I will be called a white dwarf. This will be my last stage for ever.

(i) Inner planets – (e) Earth and (g) Mars T

here are eight planets in the Solar System. The first four planets, Mercury, Venus, Earth and Mars are much nearer the Sun than the other four planets. They are called the inner planets. The inner planets have very few moons.

(ii) Outer planets – (a) Saturn The planets outside the orbit of Mars, namely Jupiter, Saturn, Uranus and Neptune are much farther off than the inner planets. They are called the outer planets. They have a ring system around them. The outer planets have large number of moons. The outer planets can be seen only with the help of large telescopes.

(iii) Constellation – (c) Great Bear and (f) Orion The stars forming a group that has a recognisable shape is called a constellation. We can easily identify them in the night sky. Ursa Major and Orion are the examples of the constellations.

(iv) Satellite of the Earth – (d) Moon Moon is the natural satellite of the Earth. It revolves around the Earth.

The Sun is the nearest star which is continuously emitting huge amount of heat and light. Hence, the Sun appears to be bigger and brighter than all the planets. The Sun is the source of almost all the energy on the Earth.

Stars having initial mass between 8 and 25 times the mass of the Sun end up as neutron stars. When these stars pass through ( the supergiant stage, their size increases to 1000 times. Huge explosion that occurs in the last stage of these stars is very powerful and very high energy is given off. After the huge explosion, called the supernova explosion, their central portion contracts in size to about 10 km. In this stage, such stars are completely made up of neutrons and hence are called neutron stars.

Mass of the star:

The star nearest to the earth is Sun.

The last stage of the Sun would be white dwarf.

Alpha Centauri.

When seen from a space-ship or Moon, the Earth appears blue-green in colour. It is due to the reflection of light from the water and landmass on its surface.

D) It is on the axis of rotation of earth

The pole star lies on the line joining the two outer stars of the constellation great bear. Pole star directly above the north pole of earth.

A pole star is a visible, preferably a prominent one, that is approximately aligned with the earth’s axis of rotation. The term polestar refers to polaris which is the current northern pole star also known as the north star. So the people in southern hemisphere unable to see this pole star.

a) It may moves towards south of the sky if it is Dakshinayanam or it may moves towards north of the sky if it is Uttarayanam. 

(So answer based upon Uttarayanam or Dakshinayanam)

b) It is travelling towards north.

c) Yes, that is the reason.

d) Yes, if it is moving towards north, the coming season is summer (in the above case it is summer) and if it is moving towards south, the coming season is winter.

The pole star appears to be stationary from the Earth, because it is situated close to the direction of the axis of rotation of the Earth. The Pole Star is not visible from the southern hemisphere. Some of the northern constellations like Ursa Major may also not be visible from some points in the southern hemisphere.

Venus is very bright that’s partly because sunlight easily reflected by acidic clouds that blanket the planet atmosphere and also it is closest planet to earth.

The pole star is situated in the direction of the earth’s axis and hence it appears as not moving.

The Pole Star is situated in the direction of the earth’s axis and that is why it does not appear to move even though all stars appear that they are moving because of the rotation of earth. So the pole star seems to be stationary.

The position of pole star is fixed and does not change. 

a) We can locate the pole star with the help of two constellations Great bear and Cassiopeia. 

b) If you are able to spot only the Great bear look at the two stars that form the outer side of rectangular head. 

c) Extend the imaginary line from these two stars. 

d) Pole star will be located on that extended line with a distance about 5 times the distance between the two stars. 

e) If only Cassiopeia is visible, the pole star will be located on the line extended from the middle star.

The polestar is situated in the direction of the earth’s axis and that is why it does not appear to move even though all stars appear that they are moving because of ie rotation of earth. So pole star seems to be stationary.

We can know the time by position of moon and stars or with reference to pole star. 

Estimation of time by using position of moon:

1. If the moon is full do the experiment stop if it is new moon. 

2. Imagine the moon is divided into 12 vertical strips. First hour at right edge and last hour at left edge. It can vary by season or location. 

3. Read the moon from left to right following an imaginary horizontal half line. 

Look for where the line intersects the boarder between light and dark. Make a note of which strip that intersection is in.

For example: 

The instruction is at 8 pm and transition from right to left is from light to dark. This tells us the moon will set in the west at 8 pm. 

This moon will set at about 7-8 hours after sunset. If sunset is at 8 pm. You can expect moon time is at 3-4 am.

If we observe the position of various stars constantly. We will notice that they are not in a fixed position because as the earth rotates about a fixed axis, the position of stars with respect to earth changes. But the position of pole star does not change with respect to earth.

1. Is stars collide with each other? 

2. Where does the stars go in the morning? 

3. Whether stars daily travel in the same path? 

4. Why night sky is black and early morning sky is blue? 

5. Whether we can count stars in the sky? 

6. Why stars grouped to form constellations?