Sun

The Sun is the star at the centre of the solar system. It is a large sphere of gas, composed mainly of hydrogen and helium. Its gravity holds the planets, moons, asteroids and comets in orbit around it.

The Sun's energy comes from nuclear fusion occurring in its core, where temperatures and pressures are extremely high. There, hydrogen atoms are converted into helium, with some of the core mass transformed into energy. This energy gradually passes outward through the Sun's layers and then escapes as light and heat.

Structure

The Sun has several distinct layers. The core is where fusion takes place. Beyond this lie the radiative zone and the convection zone, where gas moves up and down like boiling liquid. The visible surface is called the photosphere, where most of the light comes from. Above it are the chromosphere and corona, which form an extremely extended outer layer.

Magnetic activity and disturbances

The Sun has a changing magnetic field. Dark patches called sunspots appear on its surface in regions of intense magnetic activity. Explosions and energetic eruptions also occur, hurling charged material into the upper atmosphere. When these reach Earth, they can affect radio communications, satellites and power grids, and produce auroras.

Effects on Earth

Sunlight is the primary source of energy for life on Earth. It powers photosynthesis, through which plants produce food, and determines temperature and weather patterns, including winds and the water cycle. The daily cycle and seasons result from Earth's rotation and its orbit around the Sun.