What is the sun mostly made up of?

The Sun is mostly made up of hydrogen. Hydrogen accounts for roughly 73–74% of the Sun’s mass in its visible surface layer, while helium contributes most of the remainder.

The Sun is a giant sphere of extremely hot plasma rather than a solid or ordinary gas. In its core, immense pressure and temperatures of about 15 million kelvin allow hydrogen nuclei to fuse into helium. This nuclear fusion releases the energy that eventually reaches space as sunlight and heat.

The Sun formed about 4.6 billion years ago from a collapsing cloud of gas and dust that was already rich in hydrogen and helium. The core is gradually becoming richer in helium as fusion continues, but hydrogen still dominates the Sun overall. Small amounts of oxygen, carbon, neon, and iron are present, yet all heavier elements together make up less than about 2% of its mass.

A common mix-up is confusing the Sun’s composition with its energy source: hydrogen is the main material, while nuclear fusion is the process that powers the star.