Voyage Solutions for ICSE Class 9 Geography Chapter 1 Earth As A Planet

I. Short Answer Questions

Question 1. How can you prove that the earth is a sphere by looking at the Pole Star ?
Answer: The North Star is positioned directly above the Earth's axis of rotation, so it appears at an angle of 90 degrees if you stand at the North Pole. As you travel south toward the equator, the angle of the star in the sky decreases until it reaches 0 degrees at the equator. This gradual change in angle over a quarter of a circle is only possible because the Earth's surface is curved, proving it is a sphere.
In simple words: If you walk from the North Pole to the Equator, the North Star slowly sinks lower in the sky until it hits the ground line. This only happens because the Earth is round.

Exam Tip: Mention that the Pole Star's angle is 90 degrees at the North Pole and 0 degrees at the Equator to support your answer.

Question 2. Briefly describe the shape of the earth.
Answer: The Earth is a sphere that is slightly flattened at its top and bottom poles while bulging outward at its equator. We can confirm this round shape in several ways: by seeing the top mast of an incoming ship before its lower hull, by observing circular shadow shapes during lunar eclipses, by viewing circular horizons from high altitudes, and by looking at photographs taken from space satellites.
In simple words: The Earth is shaped like a slightly squashed ball, and we know this because space photos show it is round and incoming ships appear from the top down.

Exam Tip: Use the term 'oblate spheroid' to describe the Earth's shape, which means a sphere that bulges at the middle and is flat at the ends.

Question 3. What is the earth’s mean temperature ? State its one advantage.
Answer: The average temperature of the Earth is around \( 17^{\circ}\text{C} \). The main benefit of this temperature is that it is perfect for sustaining the life-support systems of all living organisms.
In simple words: The Earth's average temperature is 17 degrees Celsius, which is just right for plants, animals, and humans to live comfortably.

Exam Tip: Always write the exact number, 17 degrees Celsius, when discussing the Earth's average temperature.

Question 4. Why is the earth called a watery planet ?
Answer: The Earth is known as the watery planet because a massive portion of its surface - about 70 percent - is covered by oceans, seas, and other water bodies. This abundance of water also makes the planet look bright blue in photographs taken from outer space.
In simple words: The Earth is called the watery planet because water covers nearly three-quarters of its surface, making it look blue from space.

Exam Tip: State the percentage of water cover (70%) and its visual appearance from space (blue) to get full marks.

Question 5. What is ‘biosphere’ ?
Answer: The biosphere is the thin layer on Earth where land, water, and air meet and interact to support living organisms.
In simple words: The biosphere is the area on Earth where all life exists, where the land, water, and air come together.

Exam Tip: Define the biosphere as the meeting point of three key realms: lithosphere (land), hydrosphere (water), and atmosphere (air).

Question 6. Name the conditions necessary for life on earth.
Answer: The essential requirements for life to exist on Earth include a moderate temperature range averaging between \( 10^{\circ}\text{C} \) and \( 35^{\circ}\text{C} \), steady solar energy, air moisture, wind patterns, liquid water, and solid land.
In simple words: For life to exist, Earth needs the right temperature, sunlight, air, water, and soil.

Exam Tip: Give examples of both physical elements (water, land, wind) and climatic elements (temperature range of 10-35 degrees Celsius) in your answer.

Question 7. Give any two features of the earth that make it a ‘Unique Planet’.
Answer: 1. The Earth is the sole known planet in our solar system that supports a complex web of life.
2. It features a moderate average temperature of \( 17^{\circ}\text{C} \) along with an active atmosphere and water system that supply the essential air and liquid water needed to keep organisms alive.
In simple words: Earth is unique because it is the only planet with living things, and it has the perfect temperature, air, and water to keep them alive.

Exam Tip: Focus on the presence of life and the combination of atmosphere, hydrosphere, and moderate temperature as the two main reasons.

Question 8. Why is the planet Venus hotter than the planet Mercury?
Answer: Although Mercury is closer to the Sun, Venus is hotter because its thick atmosphere is mostly made of carbon dioxide. This gas acts like a heavy blanket, trapping the Sun's heat through a powerful greenhouse effect and driving surface temperatures to extreme levels.
In simple words: Venus is hotter than Mercury because its thick air is full of carbon dioxide, which traps heat like a giant greenhouse.

Exam Tip: Use the term 'Greenhouse Effect' and mention 'carbon dioxide' as the primary gas responsible for Venus's extreme heat.

Question 9. Name the two sources of heat in the interior of the earth.
Answer: The two main sources of heat inside the Earth are the decay of radioactive materials trapped within its layers and the extreme pressure and thermal energy left over deep in the core.
In simple words: The Earth's inside is hot because of radioactive rocks decaying and the high pressure and heat trapped deep in the core.

Exam Tip: List 'radioactive elements' and 'high pressure and core heat' as the two distinct sources of geothermal energy.

Question 10. What is meant by Terrestrial Life ?
Answer: Earth's surface is divided into landmasses and oceans. The term 'terrestrial life' refers specifically to any organisms that live and grow on land rather than in the water.
In simple words: Terrestrial life simply means animals, plants, and other living things that live on the land.

Exam Tip: Contrast terrestrial life (land-based) with aquatic life (water-based) to show a clear understanding of the term.

Question 11. Name the members of the Solar System.
Answer: The solar system consists of the Sun and all celestial bodies bound by its gravity. This includes the eight planets (Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, and Neptune), their natural moons, as well as asteroids, comets, space dust, and gas.
In simple words: Our solar system is made of the Sun, the eight planets, their moons, and smaller objects like asteroids and comets.

Exam Tip: Make sure to list the Sun as the central body and name the eight planets in order to write a complete answer.

Question 12. What is a planet ?
Answer: A planet is a large body made of rock or gas that travels along a circular path around a central star.
In simple words: A planet is a huge ball of rock or gas that orbits around a star like our Sun.

Exam Tip: Define a planet by its composition (rocky or gaseous) and its motion (orbiting a star).

Question 13. What is meant by Inner Planets ? Name them.
Answer: The four planets situated closest to the Sun, located inside the main asteroid belt, are known as the inner planets. These are Mercury, Venus, Earth, and Mars.
In simple words: The inner planets are the four rocky worlds closest to the Sun: Mercury, Venus, Earth, and Mars.

Exam Tip: Remember that the asteroid belt acts as the boundary separating the inner planets from the outer planets.

Question 14. Why are the inner planets called the terrestrial planets?
Answer: These inner worlds are termed terrestrial planets because they have a solid, rocky composition and structure similar to the Earth.
In simple words: They are called terrestrial planets because they are solid and rocky, just like Earth.

Exam Tip: The word 'terrestrial' comes from 'terra' (meaning Earth). Highlight their solid, rocky surface as the key similarity.

Question 15. What are Jovian planets ? Name them.
Answer: Jovian planets are giant worlds whose composition is similar to Jupiter's. These planets are made primarily of gases, have many moons, and feature ring systems around them. Saturn, Uranus, and Neptune belong to this group.
In simple words: Jovian planets are gas giants like Jupiter, Saturn, Uranus, and Neptune, which have rings and many moons.

Exam Tip: Contrast Jovian planets (gas giants with rings and many moons) with terrestrial planets (solid rocky bodies) in exams.

Question 16. How big is the sun ? Describe its size with respect to the earth.
Answer: The Sun is a massive star made of burning gases. Its diameter measures about 1,392,000 kilometers, which is roughly 110 times wider than the Earth, and it is large enough to hold about 1.3 million Earths inside its volume.
In simple words: The Sun is a giant ball of hot gas that is 110 times wider than Earth and over a million times bigger in total space.

Exam Tip: Use the key comparison numbers: 110 times the Earth's diameter and 1.3 million times its volume.

Question 17. Distinguish the earth from the other planets in one important aspect.
Answer: The Earth is unique among all known planets because it is the only one that possesses a thriving and diverse life system, earning it the title of the 'lonely planet'.
In simple words: Earth stands out from all other planets because it is the only place we know that has living things.

Exam Tip: Focus on the 'presence of life' or 'biosphere' as the single most critical distinguishing factor of Earth.

Question 18. How did the earth get its atmospheric blanket ?
Answer: During its early formation, the Earth was a hot mass surrounded by dense clouds of dust and gas. As the planet cooled over time, heavy metals sank toward the center to form the core, while lighter gases rose to the surface and became trapped by gravity, creating our protective atmosphere.
In simple words: When the Earth cooled down, heavy materials sank to the center while light gases rose up to form the air layer around it.

Exam Tip: Explain the separation process: heavy elements sank to form the core, and lighter gases rose to create the atmosphere.

II. Fill in the blanks

Question 1. The Pole Star can be seen at an angle of _________ at the North Pole.
Answer: 90°

Question 2. The earth rotates from _________ to _________.
Answer: west, east

Question 3. _________ is the narrow zone of contact between lithosphere, hydrosphere and atmosphere.
Answer: Biosphere

Question 4. The earth has an average temperature of _________.
Answer: 17° C

Question 5. _________ is the major reservoir of carbon on the earth.
Answer: Atmosphere

Question 6. In terms of size, the earth is _________ planet in the Solar System.
Answer: fifth

Question 7. Eratosthenes worked out the circumference of the earth to be _________ km.
Answer: 46,250

Question 8. A typical galaxy may contain _________ of stars.
Answer: large cluster

III. Long Answer Questions

Question 1. Study the picture and answer the questions that follow.
Answer:

**(a)** This illustration demonstrates the curved, spherical shape of the Earth.
**(b)** In this experiment, three poles of equal height were set up in a straight line along the Bedford Level Canal in England at 5-kilometer intervals. When viewed through a telescope, the middle pole appeared noticeably taller than the other two. This confirmed that the water's surface - and therefore the Earth's surface - is curved rather than flat.
**(c)** Sunrise and sunset occur at different times across the world because the Earth rotates from west to east, making eastern regions turn into the sunlight first. For example, Japan is known as the land of the rising sun because it sits on the eastern edge of the Eastern Hemisphere. This variation in sunrise times is direct proof of the Earth's round shape, as a flat Earth would experience sunrise everywhere at the exact same moment.
**(d)** The atmosphere is vital for life because it supplies oxygen for breathing and drives the water cycle to produce fresh rainwater. Additionally, it screens out dangerous ultraviolet radiation from the Sun and helps keep surface temperatures stable. Planets that lack an atmosphere suffer from extreme heat or freezing cold.
In simple words: The Bedford Level Experiment showed that poles of equal height in a line appear curved, which only happens on a round Earth. The atmosphere keeps us alive by giving us air and protection.

Exam Tip: Be ready to explain the Bedford Level Canal setup (three poles, 5 km intervals) and how the telescope viewing proved curvature.

Question 2. Provide reliable evidence to prove that the earth is spherical in shape.
Answer: We have multiple reliable proofs that the Earth is a sphere:
1. Space Photography: Images taken by satellites clearly show the Earth's round shape.
2. Ship Visibility: When a ship approaches the shore, its top mast becomes visible before the lower hull appears over the curved horizon.
3. Bedford Level Experiment: Placing three poles of equal height at 5-kilometer intervals shows the middle pole sitting higher, confirming surface curvature.
4. Pole Star Altitude: The angle of the North Star changes from 90 degrees at the North Pole to 0 degrees at the equator.
5. Circular Horizon: When viewed from high altitudes, the horizon always appears curved.
In simple words: We can prove the Earth is round through satellite photos, curved ship arrivals, the Bedford Level experiment, and the changing angle of the North Star.

Exam Tip: To score full marks on questions asking for proof, list at least three distinct pieces of evidence and explain them briefly.

Question 3. Give the distinctive features of the earth as a unique planet. Also give three points of comparison with respect to other planets.
Answer: The Earth is unique because it contains all the necessary conditions to support life, including a protective atmosphere, a water-rich hydrosphere, and a solid lithosphere, all under a comfortable average temperature of \( 17^{\circ}\text{C} \).

Comparison with Other Planets:
1. While other planets suffer from extreme, life-threatening temperatures (either boiling hot or freezing cold), the Earth maintains a moderate climate.
2. Many planets lack a protective air layer or are wrapped in toxic gas shrouds, whereas Earth has a breathable, life-supporting atmosphere.
3. Unlike other planets, which are completely dry, Earth has abundant fresh water in rivers, lakes, and oceans.
In simple words: Earth is the only planet with water, clean air, and a safe climate that allows plants and animals to live.

Exam Tip: Focus on comparing three key resources: temperature, atmosphere, and liquid water when contrasting Earth with other planets.

Question 4. Describe the role of each of the following in making earth a habitable planet.
(a) Atmosphere
(b) Water
(c) Temperature
Answer: **(a) Atmosphere:** The atmosphere is a critical shield that makes our planet habitable: 1. It helps regulate the Earth's thermal state by absorbing incoming solar rays and slowing the escape of outgoing terrestrial radiation. 2. It is composed of life-giving gases, chiefly nitrogen, oxygen, and carbon dioxide, which are essential for the respiration of animals and photosynthesis of plants. 3. The upper ozone layer filters out high-energy ultraviolet rays from the Sun. 4. It acts as an insulating blanket, keeping the planet warm enough to prevent liquid water from freezing solid.

**(b) Water:** Covering nearly 70 percent of the Earth's surface, water performs several vital functions: 1. It moderates climate patterns and surface temperatures globally. 2. It drives the hydrological cycle - where water continuously evaporates, condenses into clouds, and falls back to Earth as rain or snow. This constant cycle distributes fresh water and sustains terrestrial life. 3. Due to its high heat capacity, water absorbs large amounts of heat during the day, keeping the Earth cool, and slowly releases this warmth at night, preventing the surface from dropping below freezing temperatures.

**(c) Temperature:** Its position as the third planet from the Sun gives Earth a stable, moderate average temperature of \( 17^{\circ}\text{C} \). This narrow temperature envelope is ideal; even a minor shift of a few degrees would disrupt ecosystems and lead to the extinction of many species due to unbearable heat or cold.
In simple words: Our atmosphere protects us from harmful sun rays, water keeps temperatures steady through the water cycle, and the Earth's mild 17-degree climate is perfect for survival.

Exam Tip: For essays on habitability, divide your answer into these three distinct sections: Atmosphere, Water, and Temperature, providing specific points for each.

Question 5. Name the different realms of the earth.
Answer: The main physical domains of our planet are the lithosphere (land), the hydrosphere (water), and the atmosphere (air).
In simple words: The three parts of the Earth are the land, the water, and the air around it.

Exam Tip: Remember the scientific names for the three realms: lithosphere (land), hydrosphere (water), and atmosphere (air).

Question 6. Study the picture and answer the questions that follow.
Answer:

**(a)** The Solar System is composed of the Sun, the eight planets that orbit it, their natural satellites, and other bodies like asteroids and comets.
**(b)** Two primary differences between planets and stars are: 1. Stars produce and emit their own light and heat, whereas planets have no light of their own and merely reflect the light they receive from nearby stars. 2. Stars are giant, extremely hot spheres of burning gas situated very far from Earth, while planets are smaller, cooler, solid or gaseous bodies situated much closer to us.
**(c)** The terrestrial planets are the four rocky worlds located inside the main asteroid belt: Mercury, Venus, Earth, and Mars.
**(d)** The Earth holds two major advantages that make it suitable for life over other planets: 1. It maintains a moderate, habitable average temperature of \( 17^{\circ}\text{C} \). 2. It possesses a complex, active biosphere that is capable of supporting life.
**(e)** Satellites are celestial objects that travel in orbit around planets.
In simple words: The Solar System has the Sun and everything orbiting it. Stars make their own light, but planets only reflect light. Satellites are moons that go around planets.

Exam Tip: In multi-part questions, make sure to write a clear label for each part (a, b, c, d, e) and answer them in order.

Question 7. Write a short note on the planets of the Solar System. Name the planets in order of their distance from the sun.
Answer: The Solar System contains eight distinct planets that revolve around the Sun along their respective oval orbits. Listed in order of increasing distance from the Sun, these planets are Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, and Neptune.
In simple words: There are eight planets orbiting the Sun. From closest to furthest, they are Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, and Neptune.

Exam Tip: Use the classic mnemonic 'My Very Educated Mother Just Served Us Noodles' to remember the planets in order of distance.

Question 8. Distinguish between a planet and a star.
Answer: **A Planet:** 1. It moves in an orbit around a host star. 2. It does not generate any light of its own, relying on reflection. 3. It has a solid rocky or dense gaseous composition.

**A Star:** 1. It remains relatively fixed in its position at the center of its system. 2. It produces and radiates its own light and thermal energy. 3. It is a massive sphere of intensely hot, burning gases.
In simple words: Planets orbit around stars and do not glow, while stars are fixed, burning giant balls of gas that make their own light.

Exam Tip: Structure this answer with clear subheadings for 'Planet' and 'Star' and compare them point-by-point.

Practice Questions (Solved)

Question 1. In which unit the distances of universe are measured ?
Answer: Distances in outer space are measured in light years.
In simple words: Astronomers use light years to measure the huge distances between stars.

Exam Tip: Always write 'light year' as the standard unit of interstellar distance.

Question 2. How much time does a ray of sunlight take to reach the Earth ?
Answer: It takes about 8 minutes for sunlight to travel from the Sun to the Earth.
In simple words: Sunlight takes around 8 minutes to reach us on Earth.

Exam Tip: The approximate travel time is 8 minutes (or 8 minutes and 20 seconds).

Question 3. How much time does a ray of moonlight take to reach the Earth ?
Answer: Moonlight takes roughly one second to reach our planet.
In simple words: Light from the Moon takes about one second to get to Earth.

Exam Tip: State the lunar light travel time as approximately 1.3 seconds or roughly 1 second.

Question 4. How many planets are there in the Solar System ?
Answer: There are eight planets in our solar system.
In simple words: Our solar system has eight planets.

Exam Tip: Remember that Pluto is classified as a dwarf planet, leaving eight major planets.

Question 5. Name the largest planet of the Solar System.
Answer: Jupiter is the biggest planet in the solar system.
In simple words: Jupiter is the largest planet of all.

Exam Tip: Write 'Jupiter' as the largest gas giant in our solar system.

Question 6. Name the planet closest to the Sun.
Answer: Mercury is the planet situated nearest to the Sun.
In simple words: Mercury is closest to the Sun.

Exam Tip: Mercury has the shortest orbital period because of its proximity to the Sun.

Question 7. Name the planet farthest from the Sun.
Answer: Neptune is the most distant planet from the Sun.
In simple words: Neptune is the farthest planet from the Sun.

Exam Tip: Following Pluto's reclassification, Neptune is the farthest planet.

Question 8. What is position of the Earth from the Sun ?
Answer: The Earth is the third planet in order of distance from the Sun.
In simple words: The Earth is the third planet from the Sun.

Exam Tip: Recall that Earth sits between Venus and Mars as the third rock from the Sun.

Question 9. Name the planets between the Sun and the earth.
Answer: The two planets that orbit between the Sun and the Earth are Mercury and Venus.
In simple words: Mercury and Venus are the only planets closer to the Sun than Earth.

Exam Tip: These two are also known as the inner terrestrial planets.

Question 10. Which planet is known as ‘blue planet’ ?
Answer: The Earth is commonly referred to as the blue planet.
In simple words: The Earth is called the blue planet because of its water.

Exam Tip: The blue color comes from the vast oceans that cover 70% of Earth's surface.

Question 11. Which planet is known as ‘red planet’ ?
Answer: Mars is famously nicknamed the red planet.
In simple words: Mars is called the red planet because it looks red.

Exam Tip: Mars has a red color due to iron oxide (rust) on its surface.

Question 12. Which is the brightest planet ?
Answer: Venus is the most brilliant and brightest planet visible in our night sky.
In simple words: Venus is the brightest planet you can see from Earth.

Exam Tip: Venus is highly reflective because of its thick clouds of sulfuric acid.

Question 13. Which planet has the largest number of satellites ?
Answer: According to the source, Jupiter is noted as having the highest count of natural satellites.
In simple words: Jupiter is noted as having the most moons orbiting around it.

Exam Tip: While older textbooks list Jupiter, modern astronomy shows Saturn with the highest number of moons.

Question 14. Which planet has only one satellite ?
Answer: The Earth is the only planet in the solar system that has exactly one natural moon.
In simple words: The Earth has only one moon.

Exam Tip: Our single natural satellite is simply called the Moon.

Question 15. Which planet has three rings round it ?
Answer: Saturn is famous for having three prominent rings circling it.
In simple words: Saturn is the planet with three large rings around its middle.

Exam Tip: Saturn has the most spectacular ring system, composed mostly of ice and dust.

Question 16. Which star is known as ‘Evening Star or “Morning Star” ?
Answer: Venus is the celestial body commonly called the Morning Star or the Evening Star.
In simple words: Venus is known as the Morning or Evening Star because it shines brightly at dawn and dusk.

Exam Tip: Even though it is a planet, Venus gets this name because of its brightness.

Question 17. How many satellites are there in Solar System ?
Answer: There are roughly 100 known natural satellites in our solar system.
In simple words: There are about 100 moons in the solar system.

Exam Tip: State the number as approximately 100 based on standard early textbook counts.

Question 18. Which is the centre of the Solar System-Sun or Earth?
Answer: The Sun sits at the center of the solar system.
In simple words: The Sun is at the very center of the solar system.

Exam Tip: This is known as the Heliocentric model of the solar system.

Question 19. What is the period of rotation of Moon ?
Answer: The Moon takes 27 days, 7 hours, and 43 minutes to complete one full spin on its axis.
In simple words: The Moon rotates once every 27 days and nearly 8 hours.

Exam Tip: The rotation period of the Moon is equal to its revolution period, which is why we always see the same side.

Question 20. ‘Although the Moon has no light of its own, yet it shines’. Why ?
Answer: The Moon glows in the sky because it reflects the light of the Sun off its dusty surface.
In simple words: The Moon shines by reflecting sunlight like a giant mirror.

Exam Tip: Always state that the Moon is non-luminous and acts as a reflective body.

Question 21. Mention two important features of Earth that make it a planet suitable for life.
Answer: The two key elements that make the Earth habitable are:
(a) The presence of a protective gas atmosphere.
(b) The abundance of liquid water on its surface.
In simple words: Earth supports life because it has clean air to breathe and plenty of water to drink.

Exam Tip: Focus on 'atmosphere' and 'liquid water' as the two essential factors for life.

Short Answer Questions

Question 1. State three unique features of the Earth.
Answer: Three unique characteristics of our planet are:
1. It maintains a moderate climate that is neither boiling hot nor freezing cold.
2. It is enveloped by a protective, breathable atmosphere.
3. It features vast oceans and abundant liquid water on its surface.
In simple words: Earth has three special traits: it is not too hot or cold, it has air to breathe, and it has lots of water.

Exam Tip: These three points (moderate temperature, atmosphere, liquid water) are the most important elements of planetary habitability.

Question 2. State three factors which have made life possible on the Earth and on no other planet.
Answer: Several key elements combine to make Earth the only planet that supports life:
1. It maintains a perfect balance of temperature, avoiding the extreme heat or cold seen on other worlds.
2. Its atmospheric shield filters out lethal ultraviolet rays and other dangerous solar radiation.
3. The specific blend of gases in the air is ideal for biological growth and respiration.
4. Vegetation uses photosynthesis to absorb carbon dioxide and release the oxygen that animals need to breathe.
5. Large oceans cover three-fourths of the planet and drive the global water cycle, delivering fresh water to land surfaces.
6. Continuous ecological cycles distribute energy and nutrients while processing wastes to keep environments healthy.
In simple words: Earth has life because of its mild temperatures, protective air, oxygen from plants, fresh water from oceans, and recycled nutrients.

Exam Tip: Focus on how plants (producing oxygen) and oceans (driving the water cycle) work together to sustain life.

Question 3. Give reasons for the following :
(a) Earth is called a “Watery Planet”.
(b) Earth has the most ideal temperature conditions.
(c) Earth and its Moon are called a double planet.
Answer: **(a)** The Earth is called the watery planet because liquid water is abundant here, covering nearly 70 percent of its total surface area.
**(b)** The Earth enjoys optimal temperature conditions because it is located at a moderate distance from the Sun. This placement allows it to receive an ideal amount of solar heat. With an average temperature of \( 17^{\circ}\text{C} \), Earth avoids the scorching \( 500^{\circ}\text{C} \) heat of the inner planets as well as the sub-zero freezing temperatures (\( -150^{\circ}\text{C} \) to \( -200^{\circ}\text{C} \)) found on distant outer planets, remaining comfortable and habitable.
**(c)** The Earth and the Moon are sometimes referred to as a double planet system because they travel around the Sun together, sharing almost the same orbital path.
In simple words: We call Earth a watery planet because it is mostly water. Its distance from the sun keeps it warm but not burning, and the Moon orbits the Sun with us like a partner.

Exam Tip: Use comparisons (like Venus's hot surface vs Neptune's freezing surface) to explain why Earth's distance from the Sun is so ideal.

Question 4. Draw a fully labelled diagram of water cycle and explain its working and significance with reference to the diagram.
Answer: The hydrological cycle is a continuous natural process that moves water across different realms:
1. **Evaporation & Transpiration:** Liquid water absorbs solar heat and evaporates from oceans, rivers, and lakes into the atmosphere as water vapor. Plants also release moisture through transpiration.
2. **Condensation:** As this water vapor rises, it cools and condenses into clouds.
3. **Precipitation:** Once the droplets in clouds grow heavy, they fall back to the Earth as rain or snow.
4. **Runoff & Infiltration:** Rainwater either falls directly back into oceans or flows over the land through rivers and streams. Some water sinks into the ground as groundwater, eventually making its way back to the oceans.

This continuous recycling is vital because it purifies water, distributes it across land masses, and maintains a stable supply for all living things.

In simple words: The water cycle is how water travels from the ground and ocean up into the sky as clouds, and then falls back down as rain or snow in a never-ending loop.

Exam Tip: In a water cycle diagram, make sure to show all four main steps: Evaporation, Condensation, Precipitation, and Runoff.

Question 5.
(a) What makes our Sun as an ordinary star in the universe?
(b) What heavenly bodies are the members of the Solar System?
(c) Arrange the nine planet of the solar system in order of their sizes.
(d) Why do planets, being opaque bodies, shine in the sky?
Answer: **(a)** The limitless universe holds billions of galaxies, and each galaxy contains millions of stars that are very similar to our Sun. Consequently, the Sun is considered a standard, ordinary star with no unique features compared to other stars.
**(b)** The Solar System is composed of: * The Sun (the central star). * Nine planets (including dwarf planets like Pluto as listed historically). * About 63 natural satellites (moons). * A large population of small asteroids. * Millions of meteors (or shooting stars) and numerous comets. All these bodies are bound together by the Sun's strong gravitational pull.
**(c)** Arranged from largest to smallest, the planets are: 1. Jupiter 2. Saturn 3. Neptune 4. Uranus 5. Earth 6. Venus 7. Pluto 8. Mars 9. Mercury
**(d)** Although planets are solid, opaque bodies that do not produce any light, they shine in our night sky because they act like mirrors, reflecting the light they receive from the Sun.
In simple words: Our Sun is a normal star among millions of others. The solar system has the Sun, planets, moons, asteroids, and comets. Planets look bright because they reflect sunlight.

Exam Tip: Be sure to list the planets from largest (Jupiter) to smallest (Mercury) as requested, following the specific sequence given in your textbook.

Question 6. Distinguish between the following pairs.
(a) Superior and Inferior planets.
(b) Planet and Planetiods
(c) Periodical and Non-periodical comets
(d) Meteors and Meteorties
(e) Planet and Satellite.
(f) Inner and Outer planets.
Answer: **(a) Superior vs. Inferior Planets:** * **Superior Planets:** These are the six planets whose orbits lie outside the Earth's orbit. This group includes Mars, Jupiter, Saturn, Uranus, Neptune, and Pluto. * **Inferior Planets:** These are the two planets whose orbits lie closer to the Sun than the Earth's orbit. These are Mercury and Venus.

**(b) Planets vs. Planetoids:** * **Planets:** These are large celestial bodies that are easily visible and recognized as the nine planets. They travel around the Sun in elliptical paths, each taking a unique amount of time to complete its orbit. * **Planetoids (Asteroids):** These are much smaller rocky fragments or space debris. They orbit the Sun primarily in the gap between Mars and Jupiter, taking about 5 years to complete an orbit, with an estimated population of 50,000.

**(c) Periodical vs. Non-periodical Comets:** * **Periodical Comets:** These comets follow fixed, predictable paths around the Sun and appear at regular intervals. Halley's Comet is a prime example; it returns every 76 years (observed in 1910 and 1986, expected next in 2062). * **Non-periodical Comets:** These comets follow highly irregular or one-time paths, appearing very rarely and without a predictable schedule. Over 1,000 have been documented. As they approach the Sun, solar heat melts their ice, blowing dust and gas backward to create a visible tail pointing away from the Sun.

**(d) Meteors vs. Meteorites:** * **Meteors:** Commonly called shooting stars, these are streaks of light produced when stony or metallic rocky fragments burn up in Earth's atmosphere. They travel in highly eccentric orbits, with famous large events recorded in Siberia in 1908 and 1948. * **Meteorites:** These are the surviving fragments of meteors that do not burn up completely and land on the Earth's surface. Some can be massive; for example, a meteorite strike in Arizona (USA) about 5,000 years ago created a crater 180 meters deep and 1.2 kilometers (or 1,200 meters) wide.

**(e) Planets vs. Satellites:** * **Planets:** These are large, opaque bodies that revolve around the Sun, from which they originally formed. There are nine designated planets in our system, and Earth is one of them. * **Satellites (Moons):** These are smaller, spherical bodies that revolve around a specific planet. Like planets, they originated from solar material. There are 33 major natural satellites in our system, with the Moon being Earth's only satellite.

**(f) Inner vs. Outer Planets:** * **Inner Planets:** Also called terrestrial planets, these are the smaller, rocky worlds situated closest to the Sun. They have a structure similar to Earth's and include Mercury, Venus, Earth, and Mars. * **Outer Planets:** Also known as gas giants or major planets, these are much larger, less dense worlds situated beyond the asteroid belt. They include Jupiter, Saturn, Uranus, Neptune, and Pluto.
In simple words: Superior planets are outside Earth's orbit; inferior planets are inside. Planets are big; planetoids are tiny space rocks. Meteors burn up in the air, while meteorites hit the ground.

Exam Tip: For comparison questions, write separate, bold subheadings for both terms in each pair to make your answers easy to follow.

Question 7.
(a) How many satellites are there in the Solar System?
(b) Name the planet having no satellite.
(c) Which planet has the largest number of satellites.

Or
Name the largest known satellite of any planet.
Answer: **(a)** There are 57 identified natural satellites in our solar system according to early counts.
**(b)** The planets that do not have any moons are: 1. Mercury 2. Venus 3. Pluto
**(c)** Titan, which is one of the 22 moons orbiting Saturn, is the largest natural satellite in the solar system. It is physically larger than the planet Mercury and is unique because it is wrapped in a thick atmosphere of nitrogen vapor.
In simple words: There are 57 moons in the solar system. Mercury, Venus, and Pluto have no moons. Saturn's moon Titan is the largest, even bigger than the planet Mercury.

Exam Tip: Remember Titan's unique characteristics: it is Saturn's moon, larger than Mercury, and has a dense nitrogen atmosphere.

Question 8. Why are the following planets not inhabitable ?
(a) Mercury
(b) Venus
(c) Jupiter
(d) Neptune
(e) Saturn
Answer: **(a) Mercury:** 1. The side of Mercury that faces the Sun has a permanent day where temperatures soar to a burning \( 450^{\circ}\text{C} \) in a continuous summer. 2. The opposite side faces away from the Sun in permanent darkness, suffering from a freezing winter of \( -150^{\circ}\text{C} \). This creates an extremely wide day-to-night temperature range. 3. The planet lacks liquid water, and its air layer is so thin that the surface is virtually a vacuum.

**(b) Venus:** Venus is uninhabitable because its atmosphere is 96 percent carbon dioxide, trapping heat and driving surface temperatures to a maximum of \( 480^{\circ}\text{C} \), making it the hottest planet in our solar system.

**(c) Jupiter:** Jupiter cannot support life because: 1. It is extremely cold, with temperatures averaging \( -148^{\circ}\text{C} \). 2. It has no liquid water and experiences massive, violent storms across its surface. 3. It has no breathable oxygen, and its atmosphere is thick with toxic gases like ammonia, methane, and ethane.

**(d) Neptune:** Neptune is uninhabitable due to its freezing surface temperatures of \( -216^{\circ}\text{C} \) and a thick shroud of methane clouds.

**(e) Saturn:** Saturn is composed almost entirely of light gases, with a density so low that it would float if placed in a giant ocean of water. It has no solid surface to stand on, though scientists believe it has a small rocky core deep inside.
In simple words: These planets are uninhabitable because Mercury is too hot on one side and freezing on the other; Venus is boiling hot; Jupiter has massive storms and toxic air; Neptune is freezing; and Saturn is a gas giant with no solid ground.

Exam Tip: For habitability questions, state the specific reason (extreme heat, freezing cold, toxic gases, or lack of water) for each planet separately.

Question 9. Name the following
(a) Two planets which are nearer to the sun than the Earth.
(b) Two planets which are farther from the sun than the Earth.
(c) The planet farthest from the Sun.
(d) The planet nearest to the Sun.
Answer: **(a)** Mercury and Venus
**(b)** Jupiter and Saturn
**(c)** Pluto (according to historical counts)
**(d)** Mercury
In simple words: The planets closer to the Sun are Mercury and Venus; those further are Jupiter and Saturn; Mercury is closest, and Pluto is historically the furthest.

Exam Tip: Name Mercury and Venus as inner planets, and Jupiter and Saturn as outer planets in these questions.

Question 10.
(a) Which is the unit adopted for measuring the distance in the Universe ? Give a reason for its choice.
(b) Find out the number of years to reach the following celestial bodies from the Earth : Nearest star from the Earth (Distance 150 million km)
Answer: **(a)** The standard unit used to measure cosmic distances is the light year. This unit is chosen because standard kilometers are far too small to easily measure the vast distances between celestial bodies in space.
**(b)** The travel time is approximately 15.8 light years as noted.
In simple words: We use light years to measure space because kilometers are too small for the massive gaps between stars.

Exam Tip: Define a light year as the distance light travels in one year, and explain why kilometers are impractical for space scale.

Question 11. Which unit is used for measuring distances in the universe?
Answer: Distances in the universe are measured using the light year. A light year is the total distance that light travels through a vacuum in a single year, which is roughly equivalent to \( 95 \times 10^{12} \text{ km} \).
In simple words: A light year is the distance light travels in one year, which is about 95 trillion kilometers.

Exam Tip: Define the light year clearly and write down the numerical value given in your textbook.

Question 12. What makes the Sun so hot ?
Answer: The Sun is a giant, extremely hot sphere of gas that is 1.3 million times larger than Earth. Its surface temperature is approximately \( 6000^{\circ}\text{C} \), while its central core reaches an estimated \( 20,000,000^{\circ}\text{C} \). This intense thermal energy is produced by nuclear fusion, where hydrogen atoms continuously fuse together to form helium. This reaction releases massive amounts of energy, which the Sun radiates out into space as electromagnetic radiation.
In simple words: The Sun is hot because its core acts like a giant nuclear reactor, fusing hydrogen into helium and releasing huge amounts of energy.

Exam Tip: Use the term 'nuclear fusion' and explain the conversion of hydrogen into helium to explain the Sun's extreme heat.

Question 13. Name the three planets which have rings around them.
Answer: The three planets that feature ring systems are:
1. Saturn
2. Uranus
3. Neptune
In simple words: Saturn, Uranus, and Neptune all have rings around them.

Exam Tip: While Saturn has the most visible rings, Uranus and Neptune also possess faint rings.

Question 14.
Give reasons for the following :
1. Mercury completes its orbit in less time than the Earth.
2. Venus is considered as the Earth’s twin.
3. No life is possible on Saturn.
4. Pluto is the coldest planet.
5. Comets appear very rarely.
Answer: **1.** Mercury is much closer to the Sun than the Earth, orbiting at about 59 million kilometers compared to Earth's 150 million kilometers. Because its path is much shorter, Mercury takes less time to complete a full orbit.
**2.** Venus is often called Earth's twin because it is very similar to Earth in size, mass, and density, and both planets are located relatively close to each other.
**3.** Saturn cannot support life because it is a giant gas world with no solid surface and an extremely low density. It is less dense than water, meaning it would float in a giant ocean, although scientists suspect it has a small rocky core.
**4.** Pluto is extremely cold because it is the most distant planet in our system, orbiting about 40 times further from the Sun than Earth.
**5.** Comets are rarely visible because they travel along massive, highly elongated (eccentric) orbits, spending most of their time in the distant outer reaches of the solar system.
In simple words: Mercury orbits quickly because it is close to the Sun. Venus is Earth's twin because they are similar in size. Saturn is a gas giant, Pluto is freezing and far away, and comets have massive orbits.

Exam Tip: For multiple part reason-giving questions, make sure to write a clear, bold number for each part and focus on the key scientific terms like 'orbit length', 'density', or 'orbit eccentricity'.

Question 15. What do you understand by ‘Terrestrial Planet’ ?
Answer: The four planets nearest to the Sun - Mercury, Venus, Earth, and Mars - are called terrestrial planets because their solid, rocky structures are very similar to Earth's.
In simple words: Terrestrial planets are the four rocky worlds closest to the Sun: Mercury, Venus, Earth, and Mars.

Exam Tip: Highlight 'rocky composition' as the primary characteristic that terrestrial planets share with Earth.

Question 16. Why does the moon appear big in the sky though it is smaller than other heavenly bodies ?
Answer: The Moon looks large in our sky despite its small physical size because it is positioned much closer to Earth than any other celestial body.
In simple words: The Moon looks huge because it is very close to us compared to the far-away stars and planets.

Exam Tip: Use the concept of 'proximity' or 'closeness' to explain why the Moon appears larger than distant stars.

Question 17. The shape of the earth is not exactly that of a sphere Why?
Answer: The Earth is not a perfect sphere because its daily rotation on its axis creates an outward centrifugal force, which squashes the poles and causes the equator to bulge.
In simple words: The Earth is not perfectly round because its spinning motion pushes the middle outward, making it bulge at the equator.

Exam Tip: Explain that the Earth's shape is an 'oblate spheroid' caused by the centrifugal force of its rotation.

Question 18. Why is Mercury the hottest planet of the Solar System?
Answer: Mercury is the smallest planet and sits closest to the Sun, taking just 88 days to complete its orbit. Because of this proximity and its very thin atmosphere, it receives extreme solar heat, making it the hottest planet according to this text.
In simple words: Mercury is close to the Sun and has almost no atmosphere, making its sun-facing side extremely hot.

Exam Tip: State Mercury's short orbital period (88 days) and closeness to the Sun to support your answer.

Question 19. Why is Neptune the coldest planet of the Solar System?
Answer: Neptune is the most distant planet from the Sun, orbiting at a massive distance of about 6,000 million kilometers and taking 248 years to complete its journey. Because of this extreme distance, it receives very little solar heat, making it the coldest planet in our system.
In simple words: Neptune is the coldest planet because it is the furthest from the Sun and receives almost no warmth.

Exam Tip: Always list Neptune's extreme distance (6,000 million km) as the main reason for its freezing temperatures.

Question 20. ‘Venus is considered Earth’s Twin’. Why ?
Answer: Venus is referred to as Earth's twin because it shares a very similar size, mass, and density with Earth, and the two planets are situated relatively close to each other in space.
In simple words: Venus is called Earth's twin because they are almost the same size and weight.

Exam Tip: Focus on three physical qualities: size, mass (or weight), and density when comparing Venus to Earth.

Question 21.
(a) Describe the position of the Earth in Solar System.
(b) What is the size of the Earth ?
(c) Which is the satellite of the Earth ?
Answer: **(a)** The Earth is the third planet in the Solar System, orbiting in a path situated between Venus and Mars. It is shaped as an oblate spheroid.
**(b)** The physical dimensions of the Earth are: * Equatorial Diameter: 12,756 kilometers. * Polar Diameter: 12,713 kilometers. * Total Surface Area: About 51.1 crore square kilometers. * Circumference: Around 40,000 kilometers. * Mean Distance to the Sun: Approximately 14,88,00,000 kilometers. Earth is also unique as the only planet in our system that sustains life.
**(c)** The Moon is the sole natural satellite of the Earth.
In simple words: Earth is the third planet from the Sun, located between Venus and Mars. It is about 12,756 kilometers wide, has life, and has one moon.

Exam Tip: When describing Earth's size, make sure to write down both the equatorial and polar diameters as they show its oblate spheroid shape.