Our Solar System

    AQA
    GCSE

    This topic necessitates a rigorous understanding of the solar system's structure, governed by gravitational forces that maintain circular and elliptical orbits. Candidates must analyze the life cycle of stars, detailing the equilibrium between gravitational collapse and radiation pressure from nuclear fusion, and differentiate evolutionary paths based on stellar mass (e.g., neutron stars vs. white dwarfs). Furthermore, the expansion of the universe must be evidenced through the analysis of red-shift and the Doppler effect, linking observed spectral data to the Big Bang theory. Mastery of this topic requires synthesizing mechanics (orbital motion) with nuclear physics (fusion) and cosmology.

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    Objectives
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    Exam Tips
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    Pitfalls
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    Key Terms
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    Mark Points

    What You Need to Demonstrate

    Key skills and knowledge for this topic

    • Award 1 mark for stating that gravity provides the centripetal force required to maintain circular orbits
    • Credit responses that explain main sequence stability as the equilibrium between gravitational collapse and expansion due to fusion energy
    • Award 1 mark for linking observed increase in wavelength (Red Shift) to galaxies moving away from Earth
    • Candidates must state that for a stable orbit, if speed increases, the radius of the orbit must decrease (Higher Tier only)
    • Award 1 mark for identifying that elements heavier than iron are only produced during a supernova explosion

    Example Examiner Feedback

    Real feedback patterns examiners use when marking

    • "You correctly identified the stages of the star's life, but you must specify which mass category this star belongs to"
    • "Be careful with vectors: you said speed changes, but in a circular orbit, only velocity changes because the direction is changing"
    • "Good link between Red Shift and expansion. To improve, explain how the distance of the galaxy affects the amount of Red Shift observed"
    • "You mentioned gravity holds the planet in orbit; for full marks, specify that this force acts towards the centre of the circle"

    Marking Points

    Key points examiners look for in your answers

    • Award 1 mark for stating that gravity provides the centripetal force required to maintain circular orbits
    • Credit responses that explain main sequence stability as the equilibrium between gravitational collapse and expansion due to fusion energy
    • Award 1 mark for linking observed increase in wavelength (Red Shift) to galaxies moving away from Earth
    • Candidates must state that for a stable orbit, if speed increases, the radius of the orbit must decrease (Higher Tier only)
    • Award 1 mark for identifying that elements heavier than iron are only produced during a supernova explosion

    Examiner Tips

    Expert advice for maximising your marks

    • 💡When describing circular orbits, explicitly state that velocity changes because direction changes, even if speed remains constant
    • 💡Ensure you can reproduce the two distinct flowcharts for stellar evolution: one for Sun-like stars and one for massive stars
    • 💡For Red Shift questions, always chain your logic: light shifts to red end of spectrum → wavelength increases → galaxy is receding → universe is expanding

    Common Mistakes

    Pitfalls to avoid in your exam answers

    • Stating that the 'speed' of a satellite changes in a circular orbit, rather than its 'velocity' changing due to direction
    • Confusing the life cycle stages of a star similar to the Sun with those of a star much more massive than the Sun (e.g., stating the Sun will become a neutron star)
    • Describing Red Shift as galaxies moving 'through' space rather than the expansion of space itself stretching the light waves
    • Failing to link the distance of a galaxy to the speed of its recession when discussing Red Shift data

    Study Guide Available

    Comprehensive revision notes & examples

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    Key Terminology

    Essential terms to know

    Likely Command Words

    How questions on this topic are typically asked

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