The Sun is a layered star with different regions that produce, transport, and release energy into space. This cheat sheet helps students connect the Sun's internal structure to the sunlight and space weather we observe from Earth. It is useful for reviewing astronomy vocabulary, temperature patterns, and the flow of energy from the core to the outer atmosphere.
Key Facts
- The Sun's main internal layers are the core, radiative zone, and convective zone, listed from the center outward.
- The Sun's visible and atmospheric layers are the photosphere, chromosphere, transition region, and corona, listed from lower to higher altitude.
- Nuclear fusion in the core combines hydrogen into helium and releases energy, which can be summarized as 4 H nuclei -> 1 He nucleus + energy.
- The Sun's luminosity is the total power it emits, about L = 3.8 x 10^26 watts.
- Radiation carries energy through the radiative zone as photons are absorbed and reemitted many times.
- Convection carries energy through the convective zone as hot plasma rises, cools near the surface, and sinks again.
- The photosphere has an average temperature of about 5,800 K and is the layer that gives off most visible sunlight.
- The corona can reach about 1,000,000 K or more, even though it is farther from the core than the photosphere.
Vocabulary
- Core
- The central region of the Sun where nuclear fusion produces most of the Sun's energy.
- Radiative Zone
- The layer outside the core where energy moves mainly by photons being absorbed and reemitted.
- Convective Zone
- The outer interior layer where hot plasma rises and cooler plasma sinks, carrying energy by convection.
- Photosphere
- The visible surface of the Sun where most sunlight escapes into space.
- Chromosphere
- A thin reddish layer above the photosphere that is often seen during solar eclipses.
- Corona
- The Sun's outer atmosphere, a very hot and thin layer that extends far into space.
Common Mistakes to Avoid
- Calling the photosphere a solid surface is wrong because the Sun is made of hot plasma, not solid material.
- Putting the corona below the chromosphere is wrong because the corona is the Sun's outermost atmospheric layer.
- Assuming temperature always decreases outward is wrong because the corona is much hotter than the photosphere, even though the reason is complex.
- Saying fusion happens throughout the whole Sun is wrong because most fusion occurs only in the extremely hot, dense core.
- Confusing radiation with convection is wrong because radiation transfers energy by light and photons, while convection transfers energy by moving hot material.
Practice Questions
- 1 List the Sun's internal layers in order from the center outward.
- 2 The photosphere is about 5,800 K and the corona is about 1,000,000 K. About how many times hotter is the corona than the photosphere?
- 3 If the Sun's luminosity is about 3.8 x 10^26 W, how much energy does it emit in 10 seconds using energy = power x time?
- 4 Explain why energy moves by radiation in one part of the Sun and by convection in another part.