The sun is a big ball of hot gases. The gases are converted into energy in the sun's core. The energy moves outward through the interior layers, into the sun's atmosphere, and is released into the solar system as heat and light.

NASA's Solar Dynamics Observatory saw sunspot AR 1520 before the solar flare erupted from it on July 12, 2012.
NASA's Solar Dynamics Observatory saw sunspot AR 1520 before the solar flare erupted from it on July 12, 2012.
Credit: NASA/SDO (via Twitter @NASA_SDO)

Most of the gas — about 72 percent — is hydrogen. Nuclear fusion converts hydrogen into other elements. The sun is also composed of about 26 percent helium and trace amounts of other elements — oxygen, carbon, neon, nitrogen, magnesium, iron and silicon.

These elements are created in the sun's core, which makes up 25 percent of the sun. Gravitational forces create tremendous pressure and temperatures in the core. The temperature of the sun in this layer is about 27 million degrees F (15 million degrees C). Hydrogen atoms are compressed and fuse together, creating helium and a lot of energy. This process is called nuclear fusion.

The energy, mostly in the form of gamma-ray photons and neutrinos, is carried into the radiative zone. Photons can bounce around in this zone for about a million years before passing through the interface layer, or tachocline. Scientists think the sun's magnetic field is generated by a magnetic dynamo in this layer.

The convection zone is the outermost layer of the sun's interior. It extends from about 125,000 miles (200,000 km) deep up to the visible surface or the sun's atmosphere. Temperatures cool in this zone, enough for heavier ions — such as carbon, nitrogen, oxygen, calcium and iron — to hold onto their electrons. This makes the material more opaque and traps heat, causing the plasma to boil or "convect."

The convective motions carry heat quite rapidly to the surface, which is the bottom layer of the sun's atmosphere, or photosphere. This is the layer where the energy is released as sunlight. The light passes through the outer layers of the sun's atmosphere — the chromosphere and the corona — before reaching Earth eight minutes later.

Abundance of elements

Astronomers who have studied the composition of the sun have catalogued 67 chemical elements in the sun. There may be more, but in amounts too small for instruments to detect. Here is a table of the 10 most common elements in the sun:

Element Abundance (pct.
of total number
of atoms)
(pct. of total mass)
Hydrogen 91.2         71.0        
Helium 8.7         27.1        
Oxygen 0.078         0.97        
Carbon 0.043         0.40        
Nitrogen 0.0088         0.096        
Silicon 0.0045         0.099        
Magnesium 0.0038         0.076        
Neon 0.0035         0.058        
Iron 0.030         0.014        
Sulfur 0.015         0.040        

— Tim Sharp, Reference Editor