By Kenrick Vezina, Updated Aug 30, 2022
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By mass, the Sun consists of ~70% hydrogen, ~28% helium, ~1.5% carbon, nitrogen, and oxygen, and ~0.5% trace heavy elements such as neon, iron, silicon, magnesium, and sulfur.
The solar interior is dominated by two elements: hydrogen (≈70 % by mass) and helium (≈28 %). The remaining 1.5 % is a mix of carbon, nitrogen, and oxygen, while the final 0.5 % contains trace amounts of heavier species including neon, iron, silicon, magnesium, and sulfur.
Although we cannot sample solar matter directly, the Sun continuously emits electromagnetic radiation and particles. Each element absorbs and emits characteristic wavelengths, producing the Fraunhofer absorption lines first noted by William Hyde Wollaston in 1802 and later mapped by Joseph von Fraunhofer’s spectrometer.
By analysing the depth and position of these lines in the solar spectrum and measuring neutrino fluxes, researchers have quantified the Sun’s elemental composition with high precision. Modern techniques—such as high‑resolution spectroscopy and helioseismology—confirm that hydrogen and helium dominate, while heavier elements are present in trace amounts.
Stars are born when primordial hydrogen and helium gases collapse under gravity. Once core temperatures reach ~15 million K, nuclear fusion ignites, converting mass into energy according to Einstein’s equation, E = mc².
For example, when four hydrogen nuclei fuse into a helium nucleus, the resulting helium atom is 0.7 % less massive than the original four protons and neutrons. That missing mass is released as the energy that powers the Sun.
The Sun has no solid surface; its entire volume consists of ionised plasma—an energetic state of matter where atoms have lost electrons and carry net charge. This ionised gas emits light as electrons transition between energy levels, giving the Sun its brilliant glow.
The Sun’s spherical shape arises from the balance between inward gravitational forces and outward pressure from nuclear fusion. It is divided into seven distinct layers:
The corona’s high temperature (millions of degrees) overcomes the Sun’s gravity, allowing charged particles to stream outward as the solar wind. This wind shapes planetary magnetospheres and drives space weather.
With a total lifespan of ~10 billion years, the Sun is currently about 4.6 billion years old. It fuses hydrogen at a rate of ~4.27 × 10⁹ kg per second. When hydrogen depletes, the Sun will expand into a red giant, shedding outer layers and ultimately leaving a dense white dwarf roughly Earth‑sized.
