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#### Question 1:

Most stars are made up of two gases. What are these gases?

Most stars are made up of mainly two gases, which are hydrogen and helium.

#### Question 2:

The Earth is 8.3 light minutes from the Sun. What does this statement mean?

It means that the sunlight takes exactly 8.3 minutes to reach to the surface of the earth. It is calculated by dividing the distance of the earth from the sun with the speed of the light.

#### Question 3:

A constellation is a group of stars close to each other. Do you agree with this definition of a constellation? Give reasons.

A constellation is not just a group of starts close to each other, they are more like a pattern with a particular shape. When stars are divided into groups and a picture can be imagined around them, such as that of a hunter or bear, the group of starts is known a constellation.

#### Question 4:

Why does the Pole Star seem to be stationary when seen from the Earth?

Pole star appears to be stationary because it lies on the axis of rotation of the earth.

#### Question 1:

The Sun is the biggest and brightest star. Do you agree? Give reasons.

The sun is just an average sized star, there are so many other stars present in our own galaxy which are far more bigger and brighter than our sun. As the sun is closest to our earth, so it appears as the biggest and brightest star. While other stars are far far away, therefore they do not look that big and bright as much as our sun is.

#### Question 2:

Mercury does not have an atmosphere. What effect does this have on the temperature of its surface?

Mercury is very close to the sun. It is very hot during the day. Due to the absence of an atmosphere, the heat is quickly lost at night and it becomes freezing cold (About $-200°\mathrm{C}$).

#### Question 3:

Suppose the Earth's axis had not been tilted to the plane of its orbit. How would this have affected the annual seasons on the Earth?

The seasons are caused by the tilt of the earth's axis and revolution of the earth around the sun. If the earth's axis had not been tilted to the plane of its orbit then there would have been no seasons and humanity would have suffered.

#### Question 4:

Does any planet give out its own light?

No, the planets do not give their own light. They just reflect the sunlight, that's how we are able to see them.

#### Question 1:

For half the year we can see one side of the Moon, and for the other half, the other side of the Moon. Do you agree? Give reasons.

No, I do not agree with the given statement. Because the moon completes its one revolution around the earth in around 27.3 days. It also rotates once on its axis in the same period of time. Its revolution and rotation are synchronized in such a way that only one side of the moon is visible from the earth. The other side of the moon can never be seen from the earth.

#### Question 2:

Is the Moon a natural or an artificial satellite of the Earth? Why?

Moon is a natural satellite revolving around the earth. Because the moon is a celestial object revolving around the earth, it's not a human-made machine sent out to revolve in an orbit fixed by humans.

#### Question 3:

Is a shooting star actually a star? Explain.

Shooting stars look like stars but they are not stars. A shooting star is really a small piece of rock or dust that burns out and quickly shoot across the sky when it enters the earth's atmosphere.

#### Question 4:

A comet is a celestial object that revolves around the Sun like a planet. What is the difference between a comet and a planet?

Comet is a celestial body that revolves around the sun in a very long period of revolution. While a planet revolves around the sun in a short period of revolution. Also, a comet appears like a ball of fire with a long bright tail, and the size of the tail increases as it approaches the sun. While a planet revolves around the sun in a fixed orbit and it does not have any kind of tail.

#### Question 1:

A galaxy such as the Milky Way contains
(a) a few thousand stars.
(b) a few million stars.
(c) a few billion stars.
(d) only a few thousand stars but millions of planets.

(c) a few billion stars

A galaxy such as the Milky Way contains a few billion stars.

#### Question 2:

The distance of the star Proxima Centauri from the Earth is
(a) 4.3 million kilometres.
(b) $81}{4}$ light minutes.
(c) 2 million light years.
(d) 4.3 light years.

(d) 4.3 light years
Proxima Centauri is 4.3 light years away from the Earth.

#### Question 3:

The Pole Star is in the constellation of
(a) Ursa Major.
(b) Ursa Minor.
(c) Orion.
(d) Scorpius.

(b) Ursa Minor
The Pole Star is in the constellation of Ursa Minor.

#### Question 4:

The solar system consists of
(a) the Sun and the planets only.
(b) the Sun, the planets and their moons.
(c) the Sun, the planets, their moons and all other celestial objects that revolve around the Sun.
(d) all the stars in the Milky Way.

(c) the Sun, planets and their moons, and all other celestial objects that revolve around the Sun
sun and its planets  and their moon are the parts of solar system.

#### Question 5:

The hottest planet in the solar system is
(a) Mars.
(b) Sun.
(c) Mercury.
(d) Venus.

(d) Venus.

Venus is the hottest planet in the solar system.

#### Question 6:

The large number of rocks that lie between the orbits of Mars and Jupiter are called
(a) comets.
(b) asteroids.
(c) meteors.
(d) meteorites.

(b) asteroids

The large number of rocks present between the orbits of Mars and Jupiter are called asteroids.

#### Question 7:

Artificial satellites are sent in space by scientists because
(a) they look beautiful in the sky.
(b) every country wants to break the record of the largest number of satellites sent.
(c) they serve as stopovers for people going to the Moon.
(d) they are useful in communication, forecasting weather, locating minerals and in studying outer space.

(d) they are useful in communication, forecasting weather, locating minerals and in studying outer space
Artificial satellites are sent in space by scientists because they are useful in communication, forecasting weather, locating minerals and in studying outer space.

#### Question 8:

The sun is located at
(a) the centre of the solar system.
(b) the centre of the Milky Way.
(c) the centre of the universe.
(d) none of these

(a) the centre of the solar system
The sun is located at the centre of the solar system.

#### Question 1:

What are scientists studying the universe called?

Scientists studying the universe are called astronomers.

#### Question 2:

Which galaxy do we live in?

We live in a galaxy called the Milky Way.

#### Question 3:

Stars are made up of rocks. True or false?

False.
Stars are huge spinning balls of luminous gases that emit heat and light.

#### Question 4:

The Sun is hottest at its outer surface. True or false?

False.
The temperature of the centre of the Sun is about 14 million degree Celsius, while that of its surface is around 6000 degree Celsius.

#### Question 5:

What is the distance that light travels in one year called?

The distance that light travels in one year is called the light year.

#### Question 6:

The stars in a constellation are actually very close to each other. True or false?

False
A constellation is a group of stars appearing to form a pattern when viewed from the Earth.

#### Question 7:

What is the other name of the constellation Big Dipper?

The constellation Big Dipper is also known as the Ursa Major or the Great Bear.

#### Question 8:

The stars in which constellation form the shape of a hunting man?

The stars in the Orion constellation form the shape of a hunting man.

#### Question 9:

Name these:
(a) largest planet
(b) planet closest to the Sun
(c) the 'red' planet
(d) planet farthest from the Earth
(e) the hottest planet
(f) planet with high percentage of carbon dioxide in its atmosphere

(a) Largest planet - Jupiter
(b) Planet closest to the Sun - Mercury
(c) The 'red' planet - Mars
(d) Planet farthest from the Earth - Neptune
(e) The hottest planet - Venus
(f) Planet with high percentage of carbon dioxide in its atmosphere - Venus

#### Question 10:

Name the largest asteroid.

The largest asteroid is Ceres.

#### Question 11:

Which comet can be seen after every 76 years?

Halley's Comet can be seen every after 76 years.

#### Question 12:

Which was the first artificial satellite of the Earth?

Sputnik-I was the first artificial satellite of the Earth.

#### Question 13:

Which satellite was first sent into space by India?

Aryabhata was the first satellite to be sent into space by India.

#### Question 1:

While looking up at the sky, how can you distinguish between a planet and a star?

We can easily distinguish between a planet and a star by looking at the sky because stars twinkle and planets don't.

#### Question 2:

What is the solar system?

The Sun, eight planets and their moons, and other celestial bodies in the space altogether form the solar system.

#### Question 3:

Why do stars give out heat and light?

The core of the stars comprises hydrogen atoms that combine to form helium atoms. During the process of helium formation, huge amount of energy is released in the form of heat and light.

#### Question 4:

Which property of the Pole Star makes it very useful to sailors?

The Pole star is visible towards the north direction and appears to be stationary as it lies on the axis of rotation of the Earth. This property of the Pole Star makes it very useful to sailors as they can locate the north with the help of the pole star.

#### Question 5:

Why was it necessary to define a new unit to measure distances in the universe? What is this unit?

In space, the distances between the heavenly bodies are extremely large. Therefore, astronomers use a special unit called light year to measure the distance in space.

#### Question 6:

Why is Mercury very hot during the day and very cold at night?

Being very close to the Sun, Mercury turns extremely hot during the day with temperature rising above 400oC. However, Mercury's gravitational force is not strong enough to sustain the hot atmosphere. Due to the absence of this atmosphere, the heat is quickly lost at night thereby decreasing its temperature to around -200oC.

#### Question 7:

What is the most distinctive feature of Saturn?

The most distinctive feature of Saturn is that it is surrounded by three wide rings of ice and dust.

#### Question 8:

What is the difference between meteors and meteorites?

 Meteors Meteorites They are small objects made up of stones present in space. As they enter the Earth's atmosphere at a high speed, they are heated up due to friction with the atmosphere and burn to ashes before reaching the surface. If a meteor is extremely large, it does not burn out completely before reaching the Earth's surface. Such meteors are called meteorites.

#### Question 1:

Both galaxies and constellations are groups of stars. Give two differences between them.

The difference between galaxy and constellation are as follows:

 Galaxy Constellation A galaxy is a group of billion stars. A constellation is a group of a few stars that appears to form a pattern when viewed from the Earth. There are billions of galaxies in the universe. There are only 88 constellations.

#### Question 2:

How can you locate the Pole Star with the help of Ursa Major?

The constellation Ursa Major or the Great Bear is a group of seven bright stars of which Pole Star is a part.

#### Question 3:

Explain why the Pole Star appears to be stationary in the sky and all other stars appear to revolve around it from east to west.

The Pole Star lies exactly over the the Earth's axis of rotation, while the other stars don't. So, when the Earth rotates from West to East, the stars will appear to move from East to West to an observer on Earth. But the Pole Star will appear stationary to the same individual.

#### Question 4:

Show the position of main stars in these constellations:
(a) Ursa Major
(b) Orion

(a) Diagram of Ursa Major

(b) Diagram of Orion

#### Question 5:

Why is Venus the hottest planet even though Mercury is closest to the Sun?

Venus has a high percentage of carbon dioxide content in its atmosphere that results into the greenhouse effect. This is the reason why Venus is hotter than Mercury even if it is far away from the Sun.

#### Question 6:

How is an artificial satellite different from a natural satellite? Give one example of each.

A natural satellite is a celestial body that revolves around a planet. For example, Moon is the natural satellite to Earth.
On the other hand, the satellites that are contructed by the humans and launched from the Earth are called artificial satellites. These satellites revolve around the Earth much closer than its natural satellite, the Moon. For example, Sputnik-I

#### Question 7:

Describe the physical features of the Moon.

The Moon has no atmosphere and its surface is dry, barren and covered with several craters and mountains. Its diameter is one fourth of Earth's and its mass is about one hundredth that of Earth.

#### Question 1:

Give four ways in which stars are different from planets.

 Stars Planets Stars have their own light. They don't have their own light, but reflect the light of the Sun. They are made up of hot gases. They are made up of rocks. They twinkle when seen from the Earth. They do not twinkle. They are massive in size. They are smaller than stars.

#### Question 2:

What major factors have enabled life to evolve and survive on the Earth?

All the factors necessary for sustaining life-forms are present only on Earth. It has an atmosphere containing gases like oxygen and carbon dioxide, which are necessary for life. It also has abundant water, which is extremely essential for sustaining life-forms. The adequate distance of the Earth from the Sun and the suitable atmosphere around it maintain the right temperature for living organisms to survive on the Earth. It also has a ozone layer in its atmosphere to stop the harmful ultraviolet rays of the Sun from reaching the Earth's surface.

#### Question 3:

Give five ways in which artificial satellites are useful to us.

Artificial satellites are useful to us in the following ways:
1) They help in telecommunications.
2) They help in television and radio signal transmission.
3) They help us study and forecast weather by sending the pictures of clouds taken from space.
4) They help in locating minerals and studying the agricultural yield on Earth.
5) They help scientists to understand the universe by collecting various information from space.

#### Question 4:

What do you mean by 'phases of the moon'? Draw a labelled diagram to show the phases of the Moon.

The various shapes of the illuminated part of the Moon as seen throughout a month are called the phases of Moon.

Phases of the moon

#### Question 1:

Why can't we see stars during the day?

The star which is closest to Earth is Sun. During the day, the light coming from the Sun is so intense that it overpowers the light from the rest of the stars. So, it becomes difficult for us to see the other stars during the day.

#### Question 2:

Suppose a star which is 100 light years away explodes today. It is highly unlikely that you will be able to see the explosion. Why?

One light year is the distance travelled by light in a year. So, if a star which is 100 light years away explodes today, it is highly unlikely for us to see the explosion from Earth after 100 years.

#### Question 3:

On the Earth, the Sun rises in the east and sets in the west. Will it be the same on Venus?

Earth and most of the other planets rotate on their axis from West to East. So, to an observer on the Earth, Sun rises in the East and sets in the West. However, Venus rotates in the opposite direction, i.e., from East to West. So, on the planet Venus, Sun rises in the West and sets in the East.

#### Question 4:

Since your birth, how many times have you gone around the Sun?

We all know that it takes one year or 365 days for the Earth to completely revolve round the Sun. So, the number of times a person on the Earth travels around the Sun depends on his or her age.

#### Question 5:

(a) Can you light a fire on the Moon?
(b) If a meteor falls on the Moon, can you hear it fall?
(c) Can you see the meteor falling on the Moon?
(d) Can life exist on the Moon?

1. Moon has no atmosphere, nor it has oxygen that is necessary for lightning a fire. Therefore, we cannot light a fire on Moon.
2. Sound requires a mechanical medium like air for its propagation but on the Moon there is no atmosphere to carry the sound. Therefore, if a meteor falls on the Moon, we will not be able to hear it.
3. Meteors are rocks found on the space. They penetrate the atmosphere of the heavenly bodies at high speed, and get burned down to ashes due to the friction with atmosphere. As we know there is no atmosphere on the moon , we cannot see the meteor falling on the moon.
4. Moon has no atmosphere; hence, it lacks life-sustaining gases like oxygen and carbon dioxide. Therefore, life cannot exist on the Moon.

#### Question 6:

If the planet Saturn is inserted in water, will it float or sink? Why?

Saturn is entirely made up of gases that are less dense than water. Hence, if Saturn is inserted in water, it will float.

#### Question 1:

An astronomer discovered a new planet rotating on its axis and revolving around a star. He discovered that the star was about the same size as the sun. He studied the planet and discovered the following.
Average distance from the star: 145 million km
Time to orbit the star: 256 days
Time of rotation on axis: 10 hours
Axis of rotation: Perpendicular to the plane of its orbit
Water: Strong possibility of presence of water
Compare the planet with the earth on the following points.
1. Length of an year
2. Length of 1 day and 1 night
3. Seasons
4.Whether there is possibility of life

1. Length of the year on any planet is calculated by the time taken by the planet to orbit a sun. Here, time taken by the planet to orbit a sun-like star is given 256 days. Hence, the length of the year on the planet would be 256 days.

2. Length of one day and one night is decided by the time taken by the planet to rotate on its own axis. The given planet takes 10 hours to rotate on its axis. Hence, the length of one day and one night on the given planet is 10 hours long.

3. As the axis of rotation of the planet is perpendicular to the plane of the orbit, hence there would be no seasons on the given planet.

4. There is a strong possibility of the presence of water on the planet, so there are some chances that life is possible on the given planet.

#### Question 1:

Manish is interested in astronomy and wants to learn more about it. Manish's sister Kamla saved her pocket money to buy Manish a telescope on his 13th birthday. Manish is very happy now, studying the moon and planets with his telescope.
What value did Kamla show?