Topic 10 – Solar astronomy — Edexcel GCSE Astronomy
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Topic 10 – Solar astronomy explained
The Sun's interior is divided into layers whose order and relative temperatures must be known.
Read the full explanation
At the centre lies the core, where nuclear fusion releases energy at roughly 15 million kelvin, the hottest region. Surrounding it is the radiative zone, through which energy travels outward as radiation; it is cooler than the core but hotter than the layers beyond. Next comes the convective zone, where rising and sinking plasma carries energy by convection, cooler still. The outermost of these divisions is the photosphere, the visible surface, at about 5 800 K. So the sequence from centre outward is core, radiative zone, convective zone, photosphere, with temperature decreasing outward at each step.
Your focus
- Identify the core, radiative zone, convective zone and photosphere in order from the centre outward.
- State the relative temperature of each division, recognising the core as hottest and the photosphere as coolest.
- Relate each division to its dominant energy-transfer process or visible role.
Topic 10 – Solar astronomy exam tips
Marking Points
- The core is the central region where fusion occurs and is the hottest division, at roughly 15 million kelvin.
- The radiative zone lies outside the core and energy crosses it by radiation; it is cooler than the core but hotter than the convective zone.
- The convective zone lies outside the radiative zone and energy crosses it by convection; it is cooler than the radiative zone but hotter than the photosphere.
- The photosphere is the outermost of these divisions and the visible surface, at about 5 800 K, the coolest of the four.
- The correct order from the centre outward is core, radiative zone, convective zone, photosphere, with temperature decreasing outward.
Examiner Tips
- 💡Sketch the layers as concentric rings and label temperature decreasing outward to fix the order.
- 💡Use the energy-transfer name as a memory cue: radiative zone for radiation, convective zone for convection.
- 💡Check multiple-choice options by testing both position and relative temperature, since a layer can be placed correctly but given the wrong temperature.
Common Mistakes
- Reversing the layer order: the correct sequence from the centre outward is core, radiative zone, convective zone, photosphere.
- Placing the photosphere at the centre or calling it the hottest layer: it is the outermost division and the coolest of the four.
- Confusing the energy transfer in the radiative and convective zones: radiation dominates in the radiative zone and convection in the convective zone.