The source of all life

The sun is our nearest star. Its distance to Earth is some 150 million kilometers. Although it is considered the source of all terrestrial life, our sun is just average in size compared with the billions of other stars in the universe.

Stars like the sun are giant balls of gas in a hydrostatic equilibrium, which means that their inward-directed gravitational forces are balanced by the outward-directed gas and radiation pressure. The temperature and pressure are so high at the center that nuclear fusion occurs, in which hydrogen atoms are fused to helium. The energy released in the process is transported to the sun’s surface and radiated into space.

Sunspots can hinder this energy transmission because of their strong magnetic fields. This is why they are cooler and darker than their surroundings. The frequency of sunspots and thus also the sun’s activity fluctuate over about an 11-year cycle.

Facts about the sun

Age: 4.6 billion years
Diameter: 1,392,000 km
Mass: 2 x 1030 kg

at the surface: 5,750 K
in sunspots: 4,000 K
at the center: 15 million K

Chemical composition:
of the surface: 73% hydrogen, 25% helium, 2% other elements
at the center: 35% hydrogen, 63% helium, 2% other elements