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Tamil Nadu (TNBSE)Class 8 Science★ 4-7 marks in the TN Class 8 annual exam through book-back MCQs and short answers

Universe and Space Science

Samacheer Kalvi (TN State Board) Class 8 Science — Physics Chapter 8, Universe and Space Science. Celestial objects, the solar system and the planets (Mars the red planet), galaxies and constellations, satellites, how rockets work (Newton's third law), and Indian space missions (Chandrayaan-1, Mangalyaan). Notes with the actual book-back questions, common mistakes and quick revision.

⏱ 16 min readEasy difficulty✓ Free · NCERT-aligned

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By the end of this chapter you'll be able to…

1Identify celestial objects
2Name and classify the planets (Mars = red planet)
3Define a galaxy and a constellation
4Explain how rockets work (Newton's third law)
5Recall Indian space missions and their facts

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Why this chapter matters

Universe and Space Science introduces the solar system, galaxies and India's space missions, and explains how rockets work. These facts — Mars the red planet, Chandrayaan-1's date, Newton's third law — are directly tested book-back content in the TN Class 8 exam.

Before you start — revise these

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Chapter 2 — Force and Pressure

Force and Newton's laws idea.

Universe and Space Science — Class 8 Science (Samacheer Kalvi)

TN State Board (Samacheer Kalvi) Class 8 Science, Physics — Chapter 8. The solar system, galaxies, rockets and space missions.

1. About this chapter

This chapter covers celestial objects, the solar system, galaxies and constellations, satellites, how rockets work, and space missions.

2. Celestial objects and the solar system

Celestial objects are the stars, planets, the Moon, asteroids and comets in the sky.
The Sun is a star at the centre; eight planets orbit it — Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, Neptune. Mars is called the red planet.
Inner (rocky) planets: Mercury, Venus, Earth, Mars; outer (gas giants): Jupiter, Saturn, Uranus, Neptune.

3. Galaxies and constellations

A star is a huge ball of hot gas that gives out its own light.
A galaxy is a collection of billions of stars held together by mutual (gravitational) attraction; ours is the Milky Way.
A constellation is a recognisable pattern of stars (e.g., Orion, Ursa Major).

4. Satellites, rockets and missions

A natural satellite orbits a planet (the Moon orbits Earth); artificial satellites are used for communication, weather and navigation.
Rockets work on the principle of Newton's third law (action–reaction): hot gases are pushed down, so the rocket is pushed up.
Indian missions: Chandrayaan-1 (launched 22 October 2008, to the Moon) and Mangalyaan (to Mars), by ISRO.

5. Worked examples

Example 1. Which planet is called the red planet? Mars.

Example 2. On what principle do rockets work? Newton's third law (action and reaction).

Example 3. Define a galaxy. A collection of billions of stars held together by mutual attraction.

6. Book-back questions (Samacheer Kalvi)

I. Choose the correct answer

Which of the following is a celestial body? (a) Sun (b) Moon (c) Stars (d) all the above. Ans: (d).
Mangalyaan was sent to — (a) Moon (b) Mars (c) Venus. Ans: (b) Mars.
Chandrayaan-1 was launched on — (a) 22 October 2008 (b) 8 November 2008. Ans: (a) 22 October 2008.
______ is called the red planet — (a) Mercury (b) Venus (c) Mars. Ans: (c) Mars.
The working principle of rockets is — (a) Newton's first law (b) Newton's third law. Ans: (b) Newton's third law.

II. Answer briefly 6. Define a galaxy. (A collection of billions of stars held together by mutual attraction.) 7. What are celestial objects? (Stars, planets, the Moon, asteroids and comets in the sky.)

7. Common mistakes

Mistake: Counting Pluto as a planet. Fix: Pluto is a dwarf planet; there are eight planets.
Mistake: Saying rockets work on Newton's first law. Fix: Rockets work on Newton's third law (action–reaction).
Mistake: Confusing galaxy and constellation. Fix: A galaxy is billions of stars; a constellation is a star pattern in our sky.

8. Quick revision

Physics Ch 8 · celestial objects, solar system, galaxies, missions.
Celestial objects: stars, planets, Moon, asteroids, comets.
Eight planets; Mars = red planet; Milky Way is our galaxy.
Galaxy = billions of stars held by mutual attraction; rockets work on Newton's third law.
Chandrayaan-1 (22 Oct 2008, Moon) and Mangalyaan (Mars) by ISRO.

Key formulas & results

Everything you need to memorise, in one card. Screenshot this for revision.

Celestial objects

stars, planets, Moon, asteroids, comets

Objects in the sky.

Galaxy

billions of stars held by mutual attraction

Ours is the Milky Way.

Rocket principle

Newton's third law (action–reaction)

Gases down → rocket up.

Indian missions

Chandrayaan-1 (22 Oct 2008), Mangalyaan (Mars)

By ISRO.

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Common mistakes & fixes

These are the exact errors that cost students marks in board exams. Read them once, save yourself the trouble.

WATCH OUT

✗ Counting Pluto as a planet

✓ Pluto is a dwarf planet; there are eight planets.

WATCH OUT

✗ Saying rockets work on Newton's first law

✓ Rockets work on Newton's third law (action–reaction).

WATCH OUT

✗ Confusing galaxy and constellation

✓ A galaxy is billions of stars; a constellation is a star pattern in our sky.

NCERT exercises (with solutions)

Every NCERT exercise from this chapter — what it covers and how many questions to expect.

Choose the correct answer

Book-back MCQs on celestial bodies, missions, the red planet and rockets.

Questions

Answer briefly

Define galaxy and celestial objects; Indian missions.

Questions

Answer in detail

Solar system and space exploration.

Questions

Practice problems

Try each one yourself before tapping "Show solution". Active recall > rereading.

Q1EASY· MCQ

Which of the following is a celestial body? (a) Sun (b) Moon (c) Stars (d) all the above.

▶ Show solution

(d) all the above.

Q2EASY· MCQ

Mangalyaan was sent to ____.

▶ Show solution

Mars.

Q3EASY· MCQ

Chandrayaan-1 was launched on ____.

▶ Show solution

22 October 2008.

Q4EASY· MCQ

The working principle of rockets is ____.

▶ Show solution

Newton's third law (action–reaction).

Q5MEDIUM· Answer briefly

Define a galaxy.

▶ Show solution

A collection of billions of stars held together by mutual (gravitational) attraction.

Q6EASY· Answer briefly

What are celestial objects?

▶ Show solution

The stars, planets, the Moon, asteroids and comets in the sky.

5-minute revision

The whole chapter, distilled. Read this the night before the exam.

•Physics Chapter 8 of Samacheer Kalvi Class 8 Science.
•Celestial objects: stars, planets, Moon, asteroids, comets.
•Eight planets; Mars = red planet; Milky Way is our galaxy.
•Galaxy = billions of stars held by mutual attraction.
•Rockets work on Newton's third law (action–reaction).
•Chandrayaan-1 (22 Oct 2008, Moon) and Mangalyaan (Mars) by ISRO.

Tamil Nadu (TNBSE) marks blueprint

Where the marks come from in this chapter — so you can plan your prep.

Typical chapter weightage: 4-7 marks across book-back MCQ and short answers

Question type	Marks each	Typical count	What it tests
MCQ	1	2-4	Celestial bodies, planets, missions, rockets
Short Answer	2-3	1-2	Galaxy, celestial objects, missions
Long Answer	3-5	0-1	Solar system / exploration

Prep strategy

Memorise the planets and the red planet
Learn the galaxy definition
Remember rockets work on Newton's third law
Know Chandrayaan-1 and Mangalyaan facts

Where this shows up in the real world

This chapter isn't just an exam topic — it lives in the world around you.

Communication & weather

Artificial satellites enable TV, phones and forecasts.

Navigation

Satellite systems guide vehicles and ships.

Exploration

Missions like Chandrayaan and Mangalyaan study the Moon and Mars.

Exam strategy

Battle-tested tips from teachers and toppers for this chapter.

List the planets and name the red planet
Quote the galaxy definition
State rockets work on Newton's third law
Recall Chandrayaan-1 and Mangalyaan facts

Going beyond the textbook

For olympiad aspirants and curious learners — topics that build on this chapter.

Order the planets by distance from the Sun.
Explain the difference between a comet and an asteroid.

Where else this chapter is tested

CBSE board isn't the only one — other exams test this chapter too.

TN Class 8 Annual ExamHigh

Foundation / NMMS ScienceMedium

School unit testsHigh

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Questions students ask

The real ones — pulled from the Q&A community and tutor sessions.

Its surface is rich in iron oxide (rust), which gives it a reddish colour seen from Earth.

The rocket pushes hot gases downward (action); the gases push the rocket upward with an equal and opposite force (reaction), lifting it off.

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