AQA GCSE (9-1) Physics: 

Key Takeaways for GCSE Space Physics

1. Structure of the Solar System

• Planets vs. Stars:
  • Stars (e.g., the Sun) emit light via nuclear fusion.
  • Planets (e.g., Earth) orbit stars and reflect light.
• Inner vs. Outer Planets:
  • Inner (Terrestrial): Mercury, Venus, Earth, Mars. Rocky, solid surfaces.
  • Outer (Gas Giants): Jupiter, Saturn, Uranus, Neptune. Mostly gas, no solid surfaces.
• Dwarf Planets:
  • Pluto, Ceres, Eris. Spherical but not dominant in their orbits.
  • Example: Pluto was reclassified in 2006 due to similar-sized objects in its region.
• Moons: Natural satellites (e.g., Earth’s Moon, Jupiter’s 79 moons).

Tip: Use the mnemonic “My Very Educated Mother Just Served Us Noodles” for planet order.

2. Orbital Mechanics

• Gravity provides the centripetal force for orbits.
  • Planets accelerate towards the Sun, changing direction (not speed) in circular orbits.
• Orbital Speed Formula:
  v=2πrTv=T2πr​
  • Example: Earth’s orbital speed:
    v=2π×150 million km365 days≈2.6 million km/dayv=365 days2π×150 million km​≈2.6 million km/day
• Key Rule: Closer planets orbit faster (Mercury: 88 days; Neptune: 165 years).

Trick: Plotting radius vs. orbital period graphs (e.g., Saturn’s moons) shows relationships for exam questions.

3. Life Cycle of Stars

1. Formation:
   • Protostar: Gas cloud collapses under gravity, heats up.
   • Main Sequence: Hydrogen → helium fusion (e.g., the Sun).
2. Death: Depends on mass:
   • Sun-sized: Red Giant → White Dwarf → Black Dwarf.
   • Massive Stars: Red Supergiant → Supernova → Neutron Star or Black Hole.
   • Supernova spreads heavy elements (e.g., iron) into space.

Example: Elements in Earth (like gold) originated from ancient supernovae.

Tip: Memorise the sequence: Protostar → Main Sequence → Red Giant/Supergiant → Remnant.

4. Red Shift and the Big Bang Theory

• Red Shift: Light from distant galaxies shifts to longer wavelengths (lower frequency), indicating they move away from us.
  • Hubble’s Law: Speed ∝ Distance. Supports an expanding universe.
• Big Bang Theory:
  • Universe began ~13.8 billion years ago from a single point.
  • Evidence: Red shift, Cosmic Microwave Background Radiation (CMBR).

Exam Tip: Link red shift to the Doppler Effect (e.g., ambulance siren analogy).

5. Historical Models of the Solar System

• Geocentric (Aristotle): Earth-centred; flawed due to retrograde planetary motion.
• Heliocentric (Copernicus/Galileo): Sun-centred.
  • Evidence: Jupiter’s moons, Venus’s phases, Mars’s brightness changes.

Example: Galileo’s telescope observations disproved Aristotle’s model.

6. Key Equations and Definitions

• Gravitational Force: Keeps satellites in orbit.
• Velocity vs. Speed:
  • Speed = scalar (how fast).
  • Velocity = vector (speed + direction).
• Galaxy: A system of billions of stars (e.g., Milky Way).

Equation Practice: Calculate orbital speed using v=2πrTv=T2πr​ for exam tables.

7. Exam Technique

• Graph Skills: Plotting speed vs. distance for galaxies (Hubble’s Law).
• Data Analysis: Identify anomalies in orbital radius/time tables (e.g., Uranus’s outlier in Ch. 9 Q6).
• 6-Marker Tips: Structure answers using CER (Claim, Evidence, Reasoning).
  • Example: “Explain why Pluto is a dwarf planet…” → Compare size, orbital dominance, IAU criteria.

50 GCSE Space Physics Questions

Section 1: Structure of the Solar System

1. What is the difference between a star and a planet?
2. Name the four inner planets of the Solar System.
3. Why are Jupiter and Saturn classified as gas giants?
4. Explain why Pluto was reclassified as a dwarf planet in 2006.
5. How many moons does Jupiter have, and what causes this large number?
6. What is the defining characteristic of a dwarf planet?
7. List three differences between inner and outer planets.
8. What force keeps Saturn’s rings in orbit?
9. Why can’t a spacecraft land on Jupiter?
10. Name the five officially recognised dwarf planets.

Section 2: Orbital Mechanics

11. State the formula for calculating orbital speed.
12. Calculate Earth’s orbital speed using the data: radius = 150 million km, orbital period = 365 days.
13. Why does Mercury orbit the Sun faster than Neptune?
14. Explain why a planet in a circular orbit accelerates but does not change speed.
15. A comet’s orbit is highly elliptical. At which point (A, B, C, D) will it travel fastest?
16. A satellite’s speed is too slow. What happens to its orbit?
17. Plot a graph of orbital radius (y-axis) vs. time period (x-axis) for Saturn’s moons (data provided).
18. Using your graph, estimate the orbital radius of a moon with a period of 3.5 days.
19. Why does gravity not cause the Moon to collide with Earth?
20. What is the relationship between orbital radius and speed for planets?

Section 3: Life Cycle of Stars

21. Describe the stages in the life cycle of a Sun-sized star.
22. What nuclear process powers a main sequence star?
23. Why does a star become a red giant?
24. Explain why a white dwarf eventually becomes a black dwarf.
25. What happens during a supernova?
26. How are elements heavier than iron formed?
27. Why is our Solar System evidence of a past supernova?
28. Compare the life cycles of a Sun-sized star and a massive star.
29. What balances gravitational collapse in a main sequence star?
30. What is a protostar?

Section 4: Red Shift and the Big Bang

31. What is red shift?
32. How does red shift support the Big Bang theory?
33. State Hubble’s Law.
34. A galaxy is moving away at 2000 km/s. Use Hubble’s data to estimate its distance.
35. Explain the Doppler Effect analogy for red shift.
36. Why is cosmic microwave background radiation (CMBR) evidence for the Big Bang?
37. What does a blue shift in galaxy light indicate?
38. Plot a graph of galaxy speed vs. distance and describe the trend.
39. Why do scientists propose the existence of dark energy?
40. Has the Big Bang theory been proven? Explain your answer.

Section 5: Historical Models of the Solar System

41. Describe Aristotle’s geocentric model.
42. What evidence led Copernicus to propose a heliocentric model?
43. How did Galileo’s observations of Jupiter’s moons support Copernicus?
44. Why does Mars appear to move backwards in the sky (retrograde motion)?
45. Explain why Venus’s phases disproved the geocentric model.
46. What technological advancement helped Galileo confirm the heliocentric model?
47. Why did ancient astronomers believe the Sun orbited Earth?
48. Name two observations Galileo made about Venus.
49. How does Earth overtaking Mars explain its apparent motion?
50. Summarise the key evidence for the heliocentric model.

Detailed Answers

Section 1: Structure of the Solar System

1. Stars (e.g., the Sun) undergo nuclear fusion to emit light; planets (e.g., Earth) orbit stars and reflect light.
2. Mercury, Venus, Earth, Mars.
3. They are composed mostly of gas (hydrogen/helium) with no solid surface.
4. Pluto shares its orbital region with similar-sized objects (e.g., Eris).
5. 66 moons; Jupiter’s strong gravity captured debris during Solar System formation.
6. Spherical shape but does not dominate its orbit.
7. Inner: rocky, smaller, closer to Sun. Outer: gaseous, larger, farther.
8. Gravitational pull from Saturn.
9. No solid surface; spacecraft would sink into gas layers.
10. Ceres, Pluto, Haumea, Makemake, Eris.

Section 2: Orbital Mechanics

11. v=2πrTv=T2πr​
12. v=2π×150365≈2.6 million km/dayv=3652π×150​≈2.6 million km/day
13. Stronger gravitational pull closer to the Sun increases speed.
14. Acceleration changes direction (centripetal), not speed.
15. Fastest at perihelion (closest to Sun).
16. Falls to Earth (path A in Figure 8.13).
17. [Graph: Positive correlation between radius and period].
18. ~500,000 km (using extrapolation).
19. Tangential velocity balances gravitational pull.
20. Inverse relationship: Larger radius → slower speed.

Section 3: Life Cycle of Stars

21. Protostar → Main Sequence → Red Giant → White Dwarf → Black Dwarf.
22. Hydrogen fusion into helium.
23. Core hydrogen depletes; helium fusion causes expansion.
24. No fusion → cools until it emits no light.
25. Explosive collapse fuses heavy elements; disperses stellar material.
26. Formed in supernova explosions.
27. Earth contains heavy elements (e.g., iron) from supernovae.
28. Massive stars: Red Supergiant → Supernova → Neutron Star/Black Hole.
29. Outward pressure from fusion balances gravity.
30. Contracting gas cloud before fusion begins.

Section 4: Red Shift and the Big Bang

31. Light wavelength increases as galaxies move away.
32. Indicates universe expansion from a single point (Big Bang).
33. Speed ∝ Distance: v=H0×dv=H0​×d
34. Using graph: ~3400 × 10¹² km (see page 257 data).
35. Like a siren’s pitch dropping as it moves away (Doppler Effect).
36. CMBR is residual radiation from the Big Bang’s energy.
37. Galaxy is moving towards us.
38. Straight line through origin → direct proportionality.
39. Explains accelerating universe expansion.
40. Not proven but best-supported by evidence (e.g., CMBR, red shift).

Section 5: Historical Models

41. Earth-centred; planets orbit Earth at different speeds.
42. Retrograde motion explained by Earth overtaking outer planets.
43. Moons orbiting Jupiter showed not all bodies orbit Earth.
44. Earth overtakes Mars, making it appear to move backwards.
45. Phases (e.g., crescent Venus) only possible if it orbits the Sun.
46. Telescope revealed moons, phases, and planetary details.
47. Daily Sun/Moon motion appeared geocentric.
48. Phases and changing brightness.
49. Earth’s faster orbit causes apparent retrograde motion.
50. Evidence: Jupiter’s moons, Venus’s phases, Mars’s brightness changes.