The Sun: A Nuclear Furnace
- Earth & Space
- Ages 14–18 · Grades 9–12
What you’ll find out
- Fusion of hydrogen into helium in the Sun’s core converts mass into energy (E = mc²).
- Energy travels outward by radiation and convection; fusion pressure balances gravity.
- A star’s mass sets its life cycle; supernovae forge and scatter heavy elements.
No sign-up and no real names. In the lesson you check your understanding as you read, and practise until it sticks.
Fusion in the core
The Sun is an enormous sphere of hot gas, about three-quarters hydrogen and one-quarter helium. In its core the temperature reaches around 15 million degrees Celsius and the pressure is immense. Under these conditions, hydrogen nuclei collide fast enough to fuse, forming helium in a series of steps. This process, nuclear fusion, releases energy because the helium produced has slightly less mass than the hydrogen that went in; the missing mass has been converted into energy. The energy slowly works its way outward through the Sun’s layers until it escapes from the surface as light and heat. Fusion has powered the Sun for about 4.6 billion years.
The life of a star
Stars form inside vast clouds of gas and dust called nebulae. Gravity pulls clumps of gas together, and as they shrink they heat up, until the core becomes hot enough for hydrogen fusion to begin and a star is born. A star like the Sun then shines steadily for about 10 billion years. When the hydrogen in its core runs low, it swells into a red giant, later shedding its outer layers and leaving behind a small, hot white dwarf. Stars much more massive than the Sun burn their fuel far faster and end their lives in huge supernova explosions, which create heavy elements and scatter them into space.
Curriculum links: NGSS HS-ESS1-1 · NGSS HS-ESS1-3 · England KS4: Physics · Cambridge IGCSE: Physics · NCERT Physics, Class 12