AQA GCSE Physics 4.8 Space physics: a complete overview of the solar system, orbits, the life cycle of stars and the Big Bang

What topic 4.8 actually demands

Space physics is separate physics content and is more descriptive than the rest of the course, but it still rewards careful reasoning, especially about orbits and the evidence for the Big Bang. AQA tests recall of the solar system and star life cycle, the orbit reasoning, and clear explanations of red-shift and the expanding universe.

This guide walks through all three dot points of the topic, then sets out the exam patterns AQA repeats. Each dot point has a matching page with practice questions; this overview ties them together.

The solar system and orbits

The solar system has the Sun at the centre, with eight planets, their moons, and smaller bodies (dwarf planets, asteroids and comets). The Sun formed from a nebula pulled together by gravity. Gravity keeps planets orbiting the Sun and moons and satellites orbiting planets, always acting towards the centre. For a circular orbit, the speed is constant but the direction (and so velocity) changes, so the object accelerates; a stable orbit at a given radius has only one possible speed.

The life cycle of stars

A star forms from a nebula, becomes a protostar, and starts fusion to join the main sequence, where gravity is balanced by the outward pressure from fusion. A Sun-sized star becomes a red giant, then a white dwarf. A massive star becomes a red supergiant, explodes as a supernova, and leaves a neutron star or a black hole. Fusion and supernovae create and scatter the elements that form planets and us.

Red-shift and the Big Bang

Red-shift is the increase in wavelength of light from distant galaxies, showing they are moving away, faster the further away they are: evidence that the universe is expanding. This supports the Big Bang theory, that the universe began from a tiny, hot, dense point and has expanded ever since, with the cosmic microwave background radiation as key evidence. Dark matter and dark energy were proposed to explain observations the current theory cannot fully account for.

How topic 4.8 is examined

A typical AQA profile for Space physics:

• Recall. The structure of the solar system, the star life-cycle stages, and the meaning of red-shift.
• Reasoning. Why orbiting objects accelerate at constant speed, and the force balance on the main sequence.
• Evidence-based explanations. How red-shift shows expansion and how the cosmic microwave background supports the Big Bang.
• Extended answers. Describing the full life cycle of stars of different masses and the role of supernovae in making the elements.

Check your knowledge

A mix of recall and reasoning questions covering topic 4.8. Attempt them under timed conditions, then check against the solutions.

1. Name the objects that make up the solar system. (2 marks)
2. State the force that keeps a planet in orbit around the Sun. (1 mark)
3. Explain why an object in a circular orbit is accelerating even at constant speed. (2 marks)
4. Explain why a main sequence star is stable. (2 marks)
5. State the stages a Sun-sized star goes through after the main sequence. (2 marks)
6. State the stages a much more massive star goes through after the main sequence. (3 marks)
7. Explain what red-shift tells us about distant galaxies. (2 marks)
8. State one piece of evidence that supports the Big Bang theory. (1 mark)