Sun

The Sun is the star at the center of the Solar System and by far its largest component. It is a middle-aged, main-sequence star of spectral type G2V that generates energy by hydrogen fusion in its core.

It has a mass of about 1.989e30 kilograms, a radius of about 696,340 km, and a surface temperature of about 5,800 K. Its luminosity is about 3.828e26 watts.

The Sun's interior consists of a core where fusion occurs, an inner radiative zone, and an outer convective zone. The visible surface is the photosphere, with the chromosphere and corona forming the solar atmosphere. The solar wind streams outward and shapes the heliosphere.

Formation about 4.6 billion years ago from a collapsing molecular cloud. It has a lifespan on the main sequence of about 10 billion years total; is currently about halfway. It will eventually expand into a red giant and shed its outer layers, leaving a white dwarf.

The Sun exhibits magnetic activity that produces sunspots, flares, and coronal mass ejections, following an ~11-year cycle. Magnetic field drives the solar wind, which interacts with planets and creates auroras.

Earth receives energy as solar radiation; at 1 AU, the solar constant is about 1361 W/m^2. This energy drives climate and weather, supports photosynthesis, and is central to space weather considerations for satellites and astronauts.

Observations of solar neutrinos and helioseismology have informed models of stellar structure.