Exercise Solutions Available
Step-by-step answers for all textbook questions in this chapter
What is the Solar System?
The solar system is the Sun and everything that moves around it. The Sun is at the centre, and eight planets revolve around it in fixed paths called orbits. The solar system also includes the planets' moons, asteroids, comets and meteoroids — all held by the Sun's strong pull of gravity.
Celestial Bodies
Objects that exist in space are called celestial bodies. The Sun, the stars, the planets and the Moon are all celestial bodies.
| Celestial body | Has own light and heat? | Example |
|---|---|---|
| Star | Yes — gives out its own light and heat | Sun, Sirius |
| Planet | No — shines by reflecting a star's light | Earth, Jupiter |
| Satellite (Moon) | No — reflects the Sun's light | Earth's Moon |
Remember: The Sun is a star, not a planet. It looks big and bright only because it is much closer to us than the other stars.
The Sun
- The Sun is a huge ball of hot, glowing gases.
- It is the centre of the solar system.
- It gives the light and heat that make life possible on the Earth.
- The Sun is about 150 million km away from the Earth; sunlight takes about 8 minutes to reach us.
The Eight Planets
A planet is a large celestial body that revolves around a star. The eight planets of our solar system, in order from the Sun, are:
| Order | Planet | Type | One fact |
|---|---|---|---|
| 1 | Mercury | Inner / rocky | Smallest planet; closest to the Sun |
| 2 | Venus | Inner / rocky | Hottest planet; called the Earth's "twin" |
| 3 | Earth | Inner / rocky | Only planet known to support life |
| 4 | Mars | Inner / rocky | Called the Red Planet |
| 5 | Jupiter | Outer / gas giant | Largest planet |
| 6 | Saturn | Outer / gas giant | Famous for its beautiful rings |
| 7 | Uranus | Outer / gas giant | Rotates on its side |
| 8 | Neptune | Outer / gas giant | Farthest from the Sun |
Two Groups of Planets
- Inner planets (Mercury, Venus, Earth, Mars): small, rocky, with a solid surface; closer to the Sun.
- Outer planets (Jupiter, Saturn, Uranus, Neptune): very large; made mostly of gases; far from the Sun.
A Helpful Mnemonic
My Very Educated Mother Just Served Us Noodles — the first letter of each word gives the planet order: Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, Neptune.
Pluto was once called the ninth planet, but in 2006 it was reclassified as a dwarf planet. So there are now eight main planets.
The Earth — A Unique Planet
The Earth is the third planet from the Sun. It is special because:
- It is the only planet known to support life.
- It has air (atmosphere), water (hydrosphere) and land (lithosphere).
- About 71% of its surface is covered with water, so it looks blue from space — that is why the Earth is called the Blue Planet.
- Its distance from the Sun gives it a suitable temperature for living things.
The Moon
- The Moon is the Earth's only natural satellite — a smaller body that moves around a planet.
- It does not have its own light; it shines by reflecting sunlight.
- The Moon's surface is covered with craters and dust. It has no air or water, so no life exists there.
- The Moon takes about 27 days to go once around the Earth.
Asteroids, Comets and Meteoroids
| Body | What it is | Where found |
|---|---|---|
| Asteroid | A small, rocky object | In a belt between Mars and Jupiter |
| Comet | A ball of ice and dust with a glowing "tail" | Outer edges of the solar system; its tail grows as it nears the Sun |
| Meteoroid | A small piece of rock or metal | Travels through space; burns up as a "shooting star" when it enters the Earth's atmosphere |
Stars and Constellations
Stars
- Stars are huge balls of hot, glowing gases that give out their own light and heat.
- They are very far away, so they look tiny and appear to twinkle.
- The Sun is the star closest to us.
Constellations
A constellation is a group of stars that forms a recognizable pattern when seen from the Earth.
| Constellation | Also called | What to remember |
|---|---|---|
| Ursa Major | Saptarishi (the Great Bear) | Looks like a big ladle or dipper |
| Pole Star (Polaris) | Dhruva Tara | Stays almost fixed in the sky; used to find direction |
The Pole Star stays nearly in the same position in the sky while other stars appear to move around it. In earlier times, sailors and travellers used it to find direction at night.
Key Vocabulary
| Term | Meaning |
|---|---|
| Celestial body | Any object that exists in space (star, planet, moon) |
| Orbit | The fixed path on which a planet revolves around the Sun |
| Planet | A large body that revolves around a star |
| Satellite | A smaller body that revolves around a planet |
| Solar system | The Sun and all the bodies that move around it |
| Star | A hot, glowing ball of gas that has its own light and heat |
| Constellation | A group of stars forming a recognizable pattern |
| Dwarf planet | A near-planet body that has not cleared its orbit (e.g. Pluto) |
Exam Tips
- The order of the eight planets is a favourite 1-mark question — learn the mnemonic so you never forget it.
- Know the three reasons the Earth supports life: air, water and a suitable temperature.
- Blue Planet = the Earth (71% water); Red Planet = Mars — both are commonly asked.
- Be clear about the three-way difference: the Sun is a star, the Earth is a planet, the Moon is a satellite.
- For constellations, remember Ursa Major = Saptarishi and that the Pole Star is used to find direction.
- There are eight planets now (Pluto is a dwarf planet) — a common trick question.