Our star: an ordinary yellow dwarf that makes life on Earth possible.
The Sun is an ordinary star, a yellow dwarf about 4.6 billion years old. It contains about 99.8% of all the mass in the Solar System, and its diameter of about 1.39 million km is 109 times that of Earth.
How the Sun shines
In the Sun's core, at a temperature of about 15 million °C, hydrogen nuclei fuse into helium. Every second the Sun converts about four million tonnes of matter into energy. The visible surface has a temperature of about 5,500 °C.
Solar activity
The Sun's magnetic field causes sunspots, flares and eruptions. Activity rises and falls in a cycle of about 11 years. Strong eruptions can disturb satellites and power grids on Earth, and create beautiful auroras.
The image above was taken in extreme ultraviolet light by NASA's Solar Dynamics Observatory. The dark areas are coronal holes, regions from which a fast stream of solar wind escapes into space.
Never look directly at the Sun, and never through binoculars or a telescope without a certified solar filter. It can cause permanent eye damage.