AQA GCSE Physics Foundation (8463), Foundation tier · Space physics › Solar system, orbits and satellites
Practise Our solar system. 8 exam-style questions on this subtopic, at up to four difficulty levels, with full mark schemes and a progress tracker. Free, no account needed.
What makes up our solar system, how the Sun formed from a cloud of dust and gas, and why a star like the Sun stays the same size for billions of years. Expect short recall questions and 2 to 4 mark 'describe' and 'explain' questions on Paper 2. Space physics is in GCSE Physics only, not in Combined Science.
Key facts
Solar system: 1 star (the Sun), 8 planets, dwarf planets and moons
Moon = natural satellite that orbits a planet
Our solar system is a small part of the Milky Way galaxy
Nebula = cloud of dust and gas
A star forms when gravity pulls the dust and gas of a nebula together
Nuclear fusion: light nuclei join to form a heavier nucleus, releasing energy
Main sequence star: hydrogen fuses into helium in the core
Stable star: inward gravitational collapse balanced by outward expansion due to fusion energy
Notes
What is in our solar system
Our solar system has one star: the Sun.
Eight planets orbit the Sun. Dwarf planets, such as Pluto, also orbit the Sun.
Moons are natural satellites that orbit planets. They are part of the solar system too.
Our solar system is a small part of the Milky Way galaxy, which contains billions of stars.
How the Sun formed
diagram
The Sun formed from a nebula: a cloud of dust and gas (mainly hydrogen).
Gravitational attraction pulled the dust and gas together, so the cloud collapsed and became denser.
As it collapsed, energy was transferred from gravitational potential energy to the kinetic energy of the particles, so the temperature rose. This hot, collapsing ball is called a protostar.
Once fusion starts in its core, the protostar has become a star.
Nebula → protostar → star. Gravity does the pulling; fusion starts when the core is hot and dense enough.
Why a star stays the same size
diagram
Gravity pulls all the material of the star inwards (gravitational collapse).
The energy released by fusion causes an outward pressure that tends to make the star expand.
In a main sequence star these two effects are balanced (in equilibrium), so the star stays the same size.
Balanced forces (equilibrium): the star neither collapses nor expands.
The Sun is in this stable main sequence stage now, and a star like the Sun stays in it for billions of years.
How to answer each type of question
Recall: name objects in the solar system
1 mark eachGrade 3
Read exactly what is asked for, e.g. the natural satellites of planets are 'moons'.
Give one clear answer. If you write two answers and one is wrong, you can lose the mark.
Example. (a) Name the only star in our solar system. (b) How many planets orbit this star? (c) Name the galaxy that our solar system is part of.
Show the model answerHide the model answer
(a) The Sun (1) (b) Eight (1) (c) The Milky Way (1)
Describe how the Sun formed
2 to 3 marksGrade 5
Start with the nebula: a cloud of dust and gas.
Say that gravity (gravitational attraction) pulled the dust and gas together.
Say that it became hot and dense enough for fusion to start in the core.
Example. Describe how the Sun formed.
Show the model answerHide the model answer
The Sun formed from a nebula, a cloud of dust and gas (1). Gravitational attraction pulled the dust and gas together (1). The collapsing cloud became hot and dense enough for hydrogen nuclei to fuse, releasing energy (1).
Don’t lose marks
Writing 'fission' instead of 'fusion'. Stars release energy by joining light nuclei, not by splitting heavy ones.
Calling Pluto a planet (it is a dwarf planet) or saying that moons orbit the Sun (they orbit planets).
Writing 'the dust and gas came together' without saying that gravity pulled them together.
Just writing 'fusion balances gravity'. Say what fusion causes: an outward expansion (pressure) from the energy released, which balances the inward pull of gravity.
Mixing up the solar system and the galaxy: the solar system is one star and the objects orbiting it; the Milky Way is a galaxy of billions of stars.
More tips
Memory tricks
Who orbits whom: moons orbit planets, and planets and dwarf planets orbit the Sun.
Star formation chain: nebula → gravity pulls it together → hotter and denser → fusion → star. Each link is usually a mark.
Picture a tug of war that ends in a draw: gravity pulls in, fusion energy pushes out, so the star stays the same size.
Use the key words examiners look for: nebula, gravitational attraction, fusion, equilibrium.
In 'describe how the Sun formed' questions, give the steps in order. Each correct step is usually worth a mark.
For stability questions, always name both effects (inward and outward) and say that they are balanced.
In 'explain' questions about fusion starting, link each step with 'so' or 'because': gravity → collapse → temperature rises → fusion.
What each grade needs
What you need to be able to do, from the first marks up to the top grade.
Grade 3
List the objects in our solar systemOne star (the Sun), eight planets, dwarf planets such as Pluto, and moons that orbit planets.
Grade 3
Name the galaxy our solar system is inOur solar system is a small part of the Milky Way galaxy.
Grade 4
Describe how the Sun formedA nebula (a cloud of dust and gas) was pulled together by gravity until fusion started.
Grade 5
State how a star releases energyIn the core of a main sequence star, hydrogen nuclei fuse to form helium, releasing energy.
Quick recall
Cover the answers and test yourself. The app has these as flashcards that come back just before you'd forget them.
Our solar system contains many different objects. How many planets orbit the Sun?
8
Name the process that releases energy in the core of the Sun.
Nuclear fusion
A star forms from a cloud of dust and gas. The statements A, B, C and D describe stages in the formation of a star. A Fusion reactions start in the core. B Dust and gas are pulled together by gravity. C The star becomes stable, with a constant size. D The collapsing cloud becomes denser and hotter, forming a protostar. Write the letters A, B, C and D in the correct order.
B, D, A, C
State what keeps the planets in orbit around the Sun.
The Sun’s gravitational force.
Sample questions
Written for this site in the style of AQA exam questions. They are not taken from real past papers.
Question 1Easy5 marks
Our solar system contains many different objects.
(a) How many stars are there in our solar system? Tick (✓) one box.[1]
1
8
9
Millions
(b) How many planets orbit the Sun?[1]
(c) What name is given to the natural satellites that orbit planets?[1]
(d) Our solar system is a small part of a galaxy. Name this galaxy.[1]
(e) Name one other type of object, apart from planets, that orbits the Sun.[1]
Show the answer and mark scheme
(a)Answer: 1
(b)Answer: 8
8 / eight
(c)Answer: Moons
moons
(d)Answer: The Milky Way
the Milky Way
(e)Answer: Dwarf planets (e.g. Pluto)
dwarf planet
Question 2Medium6 marks
The Sun formed about 4.6 billion years ago.
(a) Describe how the Sun was formed.[3]
(b) Name the process that releases energy in the core of the Sun.[1]
(c) The size of the Sun is stable because two effects are in equilibrium. Name these two effects.[2]
Show the answer and mark scheme
(a)Answer: A cloud of dust and gas was pulled together by gravity until it was hot and dense enough for fusion to start.
from a cloud of dust and gas (a nebula)
the dust and gas were pulled together by gravity / gravitational attraction
it became hot and dense enough for (nuclear) fusion to start
(b)Answer: Nuclear fusion
(nuclear) fusion
(c)Answer: Inward gravitational collapse and outward expansion due to fusion energy.