Astronomy & Space · Unit 2

Our Solar System

The Sun, the planets, their order, and dwarf planets

The Solar System is one ordinary star and everything gravitationally bound to it, and its most striking feature is how empty it is - the planets are specks separated by enormous gaps.

The unit covers the Sun, the order of the planets, the difference between the rocky inner worlds and the gas and ice giants, and the dwarf planets that led to a change in what the word planet means.

This unit breaks down into 21 short steps and 120 questions, starting at difficulty 1 and building to 2. Below you can see exactly what it covers, how the path is structured, and worked examples with explanations.

Steps: 21
Questions: 120
Difficulty: 1-2

What this unit covers

The Rocky Inner Planets
The Sun at the Center
The Giant Outer Planets
Dwarf Planets
Order of the Planets

Where this fits

Follows The Day and Night Sky. The Planets in Depth revisits each world properly.

Where people slip

Diagrams of the Solar System are never to scale in both size and distance at once. If the planets are visible, the spacing is wrong, and that distortion shapes almost everyone's mental picture.

How the unit is structured

Our Solar System runs as 21 short steps that unlock in order. 15 are practice rounds and 6 are challenge rounds that pull together everything before them. Questions start at difficulty 1 and climb to 2 as you progress.

Step 1 · easierStep 21 · harder

Challenge rounds

Example questions

30 real questions from this unit, with the answer and the reason behind it, grouped by what they practise. There are 120 in the unit altogether.

Dwarf Planets

Choose all that applyLevel 1
1. Which of these are dwarf planets? Choose all.
- Plutocorrect
- Cerescorrect
- Eriscorrect
- Jupiter
Pluto, Ceres, and Eris are dwarf planets; Jupiter is a giant planet.
Fill the blankLevel 1
2. A ____ planet is small and round, like Pluto.
- dwarfcorrect
- giant
- gas
- rocky
Dwarf planets are round but smaller than the eight planets.
Match the pairsLevel 1
3. Match each dwarf planet to a fact about it.
Answer: Pluto = Once the ninth planet; Ceres = In the asteroid belt; Eris = A far away dwarf planet
Each dwarf planet has its own story.
Build the sentenceLevel 2
4. Build a true sentence about Pluto.
Answer: Pluto is a dwarf planet
Pluto is a dwarf planet, smaller than the eight main planets.
Fact or fibLevel 2
5. Ceres is the largest object in the asteroid belt.
Answer: True
Ceres is the biggest rock in the asteroid belt.
Guess the numberLevel 2
6. How many dwarf planets are officially named in our solar system?
Answer: 5 dwarf planets
There are five well-known dwarf planets, including Pluto and Ceres.

Order of the Planets

Build the sentenceLevel 1
7. Build a true sentence about the planets.
Answer: The planets orbit the Sun
All the planets travel in orbits around the Sun.
Fact or fibLevel 1
8. Our solar system has 8 planets.
Answer: True
There are eight planets, from Mercury out to Neptune.
Fill the blankLevel 1
9. Earth is the ____ planet from the Sun.
- thirdcorrect
- first
- second
- fourth
Counting out from the Sun, Earth is number three.
Guess the numberLevel 1
10. How many planets are in our solar system?
Answer: 8 planets
There are eight planets orbiting the Sun.
Multiple choiceLevel 1
11. Which planet comes right after Mercury as you move away from the Sun?
- Venuscorrect
- Earth
- Mars
- Jupiter
The order starts Mercury, then Venus, then Earth.
Put in orderLevel 1
12. Put these planets in order, starting from the Sun.
Answer: Mercury -> Venus -> Earth -> Mars
These are the first four planets in order from the Sun.

The Giant Outer Planets

Build the sentenceLevel 1
13. Build a true sentence about Saturn.
Answer: Saturn has beautiful rings
Saturn is famous for its beautiful rings.
Choose all that applyLevel 1
14. Which of these are giant outer planets? Choose all.
- Jupitercorrect
- Saturncorrect
- Mars
- Earth
Jupiter and Saturn are giant outer planets; Mars and Earth are rocky.
Fact or fibLevel 1
15. Saturn is famous for its rings.
Answer: True
Saturn's beautiful rings are made of ice and rock.
Fill the blankLevel 1
16. ____ is a cold blue planet far from the Sun.
- Neptunecorrect
- Mercury
- Venus
- Mars
Neptune is a chilly blue giant at the edge of the planets.
Match the pairsLevel 1
17. Match each giant planet to its special feature.
Answer: Saturn = Rings; Jupiter = Biggest planet; Neptune = Farthest planet
Each giant planet has its own special feature.
Multiple choiceLevel 1
18. Which planet is famous for its bright rings?
- Saturncorrect
- Earth
- Mercury
- Venus
Saturn's wide, shiny rings make it easy to spot.

The Rocky Inner Planets

Choose all that applyLevel 1
19. Which of these are rocky inner planets? Choose all.
- Earthcorrect
- Venuscorrect
- Marscorrect
- Neptune
Earth, Venus, and Mars are rocky inner planets; Neptune is a giant.
Fill the blankLevel 1
20. ____ is the smallest planet in our solar system.
- Mercurycorrect
- Mars
- Earth
- Pluto
Mercury is the smallest of the eight planets.
Match the pairsLevel 1
21. Match each inner planet to a fact about it.
Answer: Mercury = Smallest planet; Venus = Hottest planet; Mars = Red planet
Each inner planet has its own special fact.
Multiple choiceLevel 1
22. Which planet is the hottest of all, even hotter than Mercury?
- Venuscorrect
- Mars
- Earth
- Neptune
Venus traps heat under thick clouds, making it the hottest.
Odd one outLevel 1
23. Which one is NOT a rocky inner planet?
- Jupitercorrect
- Mercury
- Venus
- Earth
Jupiter is a giant gas planet, not a rocky inner one.
Fact or fibLevel 2
24. Mars has two small moons.
Answer: True
Mars has two tiny moons named Phobos and Deimos.

The Sun at the Center

Build the sentenceLevel 1
25. Build a true sentence about the Sun.
Answer: The Sun is a star
The Sun is a star at the center of our solar system.
Fact or fibLevel 1
26. The Sun gives us light and heat.
Answer: True
Sunlight and warmth from the Sun make life on Earth possible.
Fill the blankLevel 1
27. The Sun is a giant ball of hot ____.
- gascorrect
- rock
- ice
- water
The Sun is made of hot glowing gas, not solid rock.
Multiple choiceLevel 1
28. What sits at the center of our solar system?
- The Suncorrect
- The Earth
- The Moon
- Mars
The Sun is at the center, and everything else moves around it.
Choose all that applyLevel 2
29. Which of these are true about the Sun? Choose all.
- It is a starcorrect
- It gives light and heatcorrect
- It is at the center of the solar systemcorrect
- It is a planet
The Sun is a star at the center that gives light and heat; it is not a planet.
Guess the numberLevel 2
30. About how many minutes does sunlight take to reach Earth?
Answer: 8 minutes
Sunlight takes about eight minutes to travel to Earth.

Where these questions come from. Each unit starts as a plan of the concepts it should cover and the difficulty it should span. Questions are written against that plan with AI assistance, then checked by a validator that rejects anything without a single defensible answer, an explanation, or plausible wrong options. How we write questions sets out the whole process, and corrections are fixed in the bank and reach the site and the app the same day.

How you practise

This unit mixes 14 different question formats, so you are recalling and applying rather than recognising the same layout every time.

Build the sentence
Choose all that apply
Fact or fib
Fill the blank
Guess the number
Match the pairs
Multiple choice
Odd one out
Picture question
Put in order
Sort into groups
Spell it
True or false
Type the answer

Practise Our Solar System

120 questions across 21 steps. Start with step one and crawl at your own pace.

Play this unit

Read about Our Solar System

Explainers from our blog on what this unit covers. Each one ends with real questions from the bank.

More units in Astronomy & Space

See all 18 units in Astronomy & Space →