Exercise Solutions Available
Step-by-step answers for all textbook questions in this chapter
The Universe and Solar System — Exercise Solutions
Use this page alongside the official Samacheer Kalvi textbook. Solve every exercise question on your own first, then check the solutions below.
I. Fill in the Blanks
1. The Universe was formed after Big Bang explosion.
2. Light year is the unit used to measure the distance between two celestial bodies.
3. Sun is the centre of the solar system.
4. The word planet means Wanderer.
5. Jupiter planet has many natural satellites.
6. India's first ever mission to the moon is Chandrayaan — I.
7. Earth is inclined by 23½° degrees.
8. The Equator faces the Sun directly on 21st March and 23rd September.
9. At the time of Perihelion, the Earth is closest to the Sun.
10. The line which divides day and night on the Earth's surface is Terminator Line.
II. Choose the Best Answer (MCQs)
Q1. The movement of the Earth on its axis is called
- (a) Revolution
- (b) Seasons
- (c) Rotation
- (d) Circulation
Rotation is the spinning of the Earth on its imaginary axis from west to east, completing one rotation in about 24 hours (one day), causing day and night.
Q2. The Tropic of Capricorn faces the Sun directly on
- (a) March 21
- (b) June 21
- (c) September 23
- (d) December 22
On December 22 (Winter Solstice in the Northern Hemisphere), the Sun is directly overhead at the Tropic of Capricorn (23½°S).
Q3. The galaxy in which our solar system is found is
- (a) Andromeda
- (b) Magellanic clouds
- (c) Milky Way
- (d) Starburst
Our solar system is located in the Milky Way galaxy, which contains billions of stars. The Milky Way appears as a faint band of light in the night sky.
Q4. The only celestial body where man has successfully landed
- (a) Mars
- (b) Moon
- (c) Mercury
- (d) Venus
The Moon is the only celestial body where humans have successfully landed. Neil Armstrong became the first person to walk on the Moon on July 20, 1969, during the Apollo 11 mission.
Q5. Which of the following planets can float on water?
- (a) Jupiter
- (b) Saturn
- (c) Uranus
- (d) Neptune
Saturn is the least dense planet in the solar system. Its density (0.687 g/cm³) is less than that of water (1 g/cm³), so theoretically it could float on water if a large enough body of water existed.
Q6. Galaxy means having a huge cluster of ___
- (a) Stars
- (b) Meteors
- (c) Planets
- (d) Asteroids
A galaxy is a vast system of stars, dust, gas, and dark matter bound together by gravity. The Milky Way contains over 100 billion stars.
Q7. The somersaulting planet is ___
- (a) Venus
- (b) Neptune
- (c) Uranus
- (d) Mars
Uranus rotates on its side with an axial tilt of about 98°, making it appear to somersault (roll) along its orbit rather than spin like other planets.
Q8. ___ is self-luminous and gives light on its own
- (a) Sun
- (b) Moon
- (c) Star
- (d) Earth
The Sun is a self-luminous star that produces light and heat through nuclear fusion reactions in its core, converting hydrogen into helium.
Q9. Halley's comet will next appear in
- (a) 2051
- (b) 2041
- (c) 2061
- (d) 2031
Halley's comet appears approximately every 76 years. It was last visible in 1986, so it is expected to next appear around 2061.
Q10. The nearest planet to the Sun is
- (a) Mercury
- (b) Venus
- (c) Neptune
- (d) Jupiter
Mercury is the closest planet to the Sun, orbiting at an average distance of about 58 million kilometres.
Q11. The fifth-largest planet in the Solar System is
- (a) Jupiter
- (b) Mars
- (c) Saturn
- (d) Earth
The order of planets by size (largest to smallest) is: Jupiter, Saturn, Uranus, Neptune, Earth, Venus, Mars, Mercury. Earth is the fifth-largest planet.
Q12. Io, Europa, Ganymede, Callisto are large satellites of
- (a) Jupiter
- (b) Mars
- (c) Mercury
- (d) Venus
These four moons — Io, Europa, Ganymede, and Callisto — are known as the Galilean moons of Jupiter, discovered by Galileo Galilei in 1610. Ganymede is the largest moon in the solar system.
Q13. The second-largest planet in the solar system is
- (a) Mars
- (b) Star
- (c) Earth
- (d) Saturn
Saturn is the second-largest planet after Jupiter. It is known for its spectacular ring system made of ice and rock particles.
Q14. Saturn's largest moon is
- (a) Europa
- (b) Callisto
- (c) Titan
- (d) Titania
Titan is the largest moon of Saturn and the second-largest moon in the solar system. It is the only moon in the solar system with a dense atmosphere.
Q15. Triton is the satellite of
- (a) Earth
- (b) Jupiter
- (c) Neptune
- (d) Uranus
Triton is the largest moon of Neptune. It is unique because it orbits Neptune in a retrograde direction (opposite to Neptune's rotation).
Q16. Pick out the leap year:
- (a) 2001
- (b) 2014
- (c) 2018
- (d) 2020
A leap year is divisible by 4 (but not by 100, unless also by 400). 2020 is divisible by 4, so it is a leap year. 2001, 2014, and 2018 are not.
Q17. A solid layer of rocks and soil is found in:
- (a) Biosphere
- (b) Lithosphere
- (c) Hydrosphere
- (d) Atmosphere
The lithosphere is the solid, rocky outer layer of the Earth, comprising the crust and the uppermost part of the mantle. It contains rocks, soil, and minerals.
III. Odd One Out
Q1. Venus, Jupiter, Neptune, Saturn
Venus is an inner (terrestrial) planet. Jupiter, Neptune, and Saturn are outer (Jovian/gaseous) planets.
Q2. Sirius, Andromeda, Milky Way, Magellanic clouds
Sirius is a star. Andromeda, Milky Way, and Magellanic clouds are galaxies.
Q3. Pluto, Eris, Ceres, Io
Io is a moon (satellite of Jupiter). Pluto, Eris, and Ceres are dwarf planets.
Q4. Comet, Asteroids, Meteorites, Dwarf planets
Dwarf planets are a distinct category of celestial bodies. Comets, asteroids, and meteorites are small celestial bodies/debris.
Q5. Rover, Orbiter, Aeroplane, Space shuttle
An aeroplane is not a space vehicle. Rovers, orbiters, and space shuttles are all designed for space exploration.
IV. Match the Following
| # | Column A | Column B | Match |
|---|---|---|---|
| 1 | Hottest Planet | (a) Mars | (c) Venus |
| 2 | Ringed Planet | (b) Neptune | (d) Saturn |
| 3 | Red Planet | (c) Venus | (a) Mars |
| 4 | Somersaulting Planet | (d) Saturn | (e) Uranus |
| 5 | Coldest Planet | (e) Uranus | (b) Neptune |
V. Consider the Following Statements
Q1. Consider the following statements: 1. Venus rotates from east to west. 2. Tropic of Cancer faces Sun on June 21. 3. Mars has rings around it.
- (a) 1 and 2
- (b) 2 and 3
- (c) 1, 2 and 3
- (d) 2 only
Statement 1 is correct: Venus rotates from east to west (retrograde rotation). Statement 2 is correct: On June 21 (Summer Solstice), the Sun is directly overhead at the Tropic of Cancer. Statement 3 is wrong: Mars does not have rings; Saturn, Jupiter, Uranus, and Neptune have rings.
Q2. Statement I: Earth is called a watery planet. Statement II: Rotation of Earth causes seasons.
- (a) I is true; II is wrong
- (b) I is wrong; II is true
- (c) Both the statements are true
- (d) Statements I and II are wrong
Earth is called the watery (or blue) planet because about 71% of its surface is covered by water. However, revolution (not rotation) causes seasons. Rotation causes day and night.
VI. Name the Following
1. Cluster of stars → Galaxy
2. Nearest galaxy to the solar system → Andromeda (also accepted: Magellanic clouds, which are satellite galaxies of the Milky Way)
3. Brightest planet → Venus
4. Living sphere → Biosphere (Earth)
5. Year with 366 days → Leap year
VII. Very Short Answer Questions
Q1. Name the inner planets.
Q2. Why is Pluto no longer a planet?
Q3. What is Perihelion?
Q4. When is the Sun overhead at 20°N latitude?
Q5. Name a celestial body that shares its orbit with other objects.
VIII. Short Answer Questions
Q1. Give reasons:
**(a) Why is Uranus called the somersaulting planet?
**(b) Why does the Moon have craters?
**(c) Why is the rotation velocity zero at the poles?
Q2. Distinguish between inner planets and outer planets.
| Feature | Inner Planets | Outer Planets |
|---|---|---|
| Names | Mercury, Venus, Earth, Mars | Jupiter, Saturn, Uranus, Neptune |
| Position | Close to the Sun | Far from the Sun |
| Size | Smaller in size | Much larger in size |
| Composition | Rocky surface (terrestrial) | Gaseous (Jovian) |
| Moons | Few or no moons | Many moons |
| Rings | No rings | Have ring systems |
| Examples | Earth (blue planet), Mars (red planet) | Saturn (ringed planet), Jupiter (largest) |
Q3. What are the effects of rotation and revolution of the Earth?
Effects of Rotation
- Causes day and night — the side facing the Sun has day, the opposite side has night
- Creates a difference in time between places at different longitudes (time zones)
- Causes the Coriolis effect — deflection of winds and ocean currents
- Tides rise and fall due to the combined effect of rotation and the Moon's gravity
Effects of Revolution
- Causes seasons — summer, winter, spring, and autumn
- Creates solstices — June 21 (Summer Solstice in Northern Hemisphere) and December 22 (Winter Solstice)
- Creates equinoxes — March 21 and September 23, when day and night are equal
- Varies the length of day and night throughout the year
Q4. Write about the spheres of the Earth.
| Sphere | Description | Components |
|---|---|---|
| Lithosphere | The solid, rocky outer layer of the Earth | Crust, upper mantle, rocks, soil, minerals, mountains |
| Hydrosphere | All the water on the Earth's surface | Oceans, seas, rivers, lakes, glaciers, groundwater, water vapour |
| Atmosphere | The layer of gases surrounding the Earth | Nitrogen (78%), Oxygen (21%), other gases, water vapour, dust particles |
| Biosphere | The living zone where all three spheres interact | Plants, animals, microorganisms — the zone where life exists |
The biosphere overlaps with all three other spheres. Life exists in the lithosphere (on land), hydrosphere (in water), and atmosphere (in the air near the surface).
Q5. Write a brief note on the Sun.
- The Sun is a self-luminous star at the centre of the solar system
- It is made up of hot, glowing gases — primarily hydrogen and helium
- It produces light and heat through nuclear fusion — converting hydrogen into helium
- Its surface temperature is about 6,000°C and the core temperature is about 15 million°C
- The Sun's diameter is about 1.39 million km — about 109 times the diameter of Earth
- It is the primary source of energy for all life on Earth
- The Sun accounts for 99.86% of the total mass of the solar system
Q6. Write a brief note on comets and asteroids.
Comets
- Comets are icy celestial bodies made of dust, rock, and frozen gases
- They have a bright head (coma) and a long tail that always points away from the Sun
- They orbit the Sun in highly elliptical (elongated) paths
- Example: Halley's Comet, which appears approximately every 76 years (next expected in 2061)
Asteroids
- Asteroids are small, rocky bodies that orbit the Sun
- Most asteroids are found in the asteroid belt between Mars and Jupiter
- They are irregular in shape and vary in size
- Asteroids are also called minor planets or planetoids
IX. Detailed / Long Answer Questions
Q1. Explain the composition of the solar system with a diagram description.
1. The Sun — the star at the centre; contains 99.86% of the solar system's mass 2. Eight Planets (in order from the Sun):
3. Dwarf Planets — Pluto, Eris, Ceres (do not clear their orbital neighbourhood) 4. Moons (Satellites) — natural satellites orbiting planets (e.g., Moon for Earth, Titan for Saturn) 5. Asteroids — small rocky bodies, mainly in the asteroid belt between Mars and Jupiter 6. Comets — icy bodies with long tails (e.g., Halley's Comet) 7. Meteorites — small pieces of rock or metal that burn up in Earth's atmosphere (shooting stars)
- Mercury — smallest planet, closest to the Sun, no atmosphere
- Venus — hottest planet, rotates east to west, brightest planet
- Earth — blue planet, only known planet with life
- Mars — red planet, has the largest volcano (Olympus Mons)
- Jupiter — largest planet, has the Great Red Spot, 79+ moons
- Saturn — ringed planet, can float on water, second-largest
- Uranus — somersaulting planet, tilted 98°, appears greenish
- Neptune — coldest planet, farthest from the Sun
Q2. Describe the planets of the solar system in detail.
Inner (Terrestrial) Planets
| Planet | Key Features |
|---|---|
| Mercury | Closest to the Sun, smallest planet, no atmosphere, extreme temperatures |
| Venus | Hottest planet (greenhouse effect), rotates east to west, brightest planet, called Earth's twin |
| Earth | Blue planet, only planet with life, 71% water, 23½° axial tilt, one moon |
| Mars | Red planet (iron oxide), thin atmosphere, two small moons — Phobos and Deimos |
Outer (Jovian/Gaseous) Planets
| Planet | Key Features |
|---|---|
| Jupiter | Largest planet, Great Red Spot (storm), 79+ moons including Galilean moons (Io, Europa, Ganymede, Callisto) |
| Saturn | Ringed planet, least dense planet, can float on water, largest moon is Titan |
| Uranus | Somersaulting planet (98° tilt), appears greenish, discovered by William Herschel |
| Neptune | Coldest planet, farthest from the Sun, largest moon is Triton |
Q3. Explain the seasons of the Earth with the concepts of solstices and equinoxes.
Solstices
- Summer Solstice (June 21): The Sun is directly overhead at the Tropic of Cancer (23½°N). Northern Hemisphere has the longest day and shortest night. It is summer in the Northern Hemisphere and winter in the Southern Hemisphere.
- Winter Solstice (December 22): The Sun is directly overhead at the Tropic of Capricorn (23½°S). Northern Hemisphere has the shortest day and longest night. It is winter in the Northern Hemisphere and summer in the Southern Hemisphere.
Equinoxes
- Vernal Equinox (March 21): The Sun is directly overhead at the Equator. Day and night are of equal duration all over the world.
- Autumnal Equinox (September 23): The Sun is directly overhead at the Equator again. Day and night are equal everywhere.
Seasons in Tamil Nadu (Northern Hemisphere)
- Summer: March to May (temperature rises, Sun moves northward)
- Southwest Monsoon: June to September (rainy season)
- Northeast Monsoon: October to December (rainy season in Tamil Nadu)
- Winter: January to February (cool season)
Q4. Write about India's space programme.
Key Milestones
1. ARYABHATA (1975) — India's first satellite, launched with Soviet assistance 2. Chandrayaan-I (2008) — India's first lunar mission; discovered water molecules on the Moon 3. Mangalyaan / MOM (2013) — India's Mars Orbiter Mission; India became the first Asian country and the first country to succeed in its maiden attempt to reach Mars 4. Chandrayaan-II (2019) — Second lunar exploration mission; orbiter successfully reached lunar orbit 5. Chandrayaan-III (2023) — Successfully landed on the Moon's south pole; India became the fourth country to soft-land on the Moon
Space Organisations
- ISRO (Indian Space Research Organisation) — India's national space agency, headquartered in Bengaluru
- Established in 1969; ISRO has made significant achievements in satellite technology, launch vehicles, and space exploration at low cost
Significance
- Satellite communication and broadcasting
- Weather forecasting (INSAT satellites)
- Navigation (IRNSS / NavIC)
- Remote sensing for agriculture, disaster management, and resource mapping
Common Mistakes to Avoid
1. Confusing rotation and revolution. Rotation = Earth spinning on its axis (causes day and night, 24 hours). Revolution = Earth orbiting around the Sun (causes seasons, 365¼ days). Do NOT say "rotation causes seasons."
2. Saying Saturn is the only planet with rings. Jupiter, Uranus, and Neptune also have ring systems. Saturn's rings are simply the most visible and spectacular.
3. Confusing inner and outer planets. Inner planets (Mercury, Venus, Earth, Mars) are rocky/terrestrial. Outer planets (Jupiter, Saturn, Uranus, Neptune) are gaseous/Jovian. Do not mix them up.
4. Thinking Venus is the closest planet to the Sun. Mercury is the closest. Venus is the second planet. Venus is the hottest (due to greenhouse effect), not the closest.
5. Writing "Earth rotates from north to south." Earth rotates from west to east (counterclockwise when viewed from above the North Pole). Venus rotates from east to west (retrograde).
6. Confusing Perihelion and Aphelion. Perihelion = Earth is closest to the Sun (January 3). Aphelion = Earth is farthest from the Sun (July 4). A trick: "Peri" means near, "Ap" means away.
7. Forgetting the Earth's axial tilt. Seasons are caused by the 23½° tilt of the Earth's axis combined with revolution — not by the distance from the Sun. If there were no tilt, there would be no seasons.
Exam Checklist
Before your exam, make sure you can:
- [ ] Define galaxy, star, planet, and distinguish between them
- [ ] List all eight planets in order from the Sun and classify them as inner/outer
- [ ] Explain why Earth is called the Blue Planet and the watery planet
- [ ] Describe the effects of rotation (day and night) and revolution (seasons)
- [ ] Explain solstices (June 21, December 22) and equinoxes (March 21, September 23)
- [ ] Identify the special features of each planet (Venus = hottest, Mars = red, Saturn = rings, Uranus = somersaulting, Neptune = coldest)
- [ ] Distinguish between inner (terrestrial) and outer (Jovian) planets with a comparison table
- [ ] Explain the four spheres of the Earth (Lithosphere, Hydrosphere, Atmosphere, Biosphere)
- [ ] Define light year, perihelion, terminator line, leap year
- [ ] Write about comets, asteroids, meteorites, and dwarf planets
- [ ] Name India's space missions (Chandrayaan-I, II, III, Mangalyaan) and their significance
- [ ] Answer odd-one-out and match-the-following questions correctly by knowing planet features
- [ ] Explain why the Moon has craters and why rotation velocity is zero at the poles