Science & history · Inside and above
What powers the Sun?
The Sun shines because its core is hot and dense enough for hydrogen nuclei to fuse into helium.
Fusion in the core
The Sun makes energy through the fusion of hydrogen into helium at its core. The core is about 15 million degrees Celsius, with a density of about 150 grams per cubic centimetre: some thirteen times the density of lead, and still a gas.
A balance
The pressure produced by fusion pushes outwards; the Sun's gravity pulls inwards. The two are in equilibrium, which is why the Sun has stayed much the same size for billions of years instead of collapsing or flying apart.
Sources
- NASA Science How does the Sun make energy? (opens in a new tab) for fusion of hydrogen into helium in the core; balance of pressure and gravity · checked 2 October 2026
- NASA Sun: Facts (opens in a new tab) for age, size, distance, temperatures, layers, rotation, cycle, type, future · checked 2 October 2026