Space and Time
Size: Diameter 1,390,000km
Mass: 1.989e30kg
Composition: Mostly hydrogen (75% hydrogen, 25% helium)
Mean temperature: Surface: 5,800°C, core: 15,600,000°C
The Sun is the nearest star to Earth, about 150 million km away. It supports all life on our planet, providing warmth and light. It powers photosynthesis in green plants and is ultimately the source of all food and fossil fuels.
The Sun contains 99.86 percent of all the mass in the solar system. The next largest body, Jupiter, contains most of the rest. The Sun is 333,400 times bigger than Earth.
The Sun's energy output, about 386 billion billion megawatts, is produced by nuclear fusion reactions within the core. Each second about 700,000,000 tons of hydrogen are converted to about 695,000,000 tons of helium and 5,000,000 tons of energy in the form of gamma rays. This is roughly the equivalent to the energy of 100 billion tons of dynamite exploding every second.
As well as the energy-producing core, the interior has two distinct regions: a radiative zone and a convective zone. It takes a few hundred thousand years for photons to escape from the dense core and reach the surface.
A large, eruptive prominence with an image of the Earth added for size comparison. Prominences are huge clouds of relatively cool dense plasma suspended in the Sun's hot, thin corona. At times they can erupt, escaping the Sun's atmosphere. This prominence from 24 July 1999 is particularly large and looping, extending over 35 Earths out from the Sun.
The Sun's 'surface', known as the photosphere, is the visible 500km-thick layer from which most of the Sun's radiation and light finally escape. Above the photosphere lies the chromosphere ('sphere of colour') that may be seen briefly during total solar eclipses as a reddish rim, caused by hot hydrogen atoms, around the Sun.
Above the chromosphere lies the corona ('crown'), extending outward from the Sun in the form of the 'solar wind' to the edge of the solar system.
Mankind has been fascinated by the Sun for thousands of years. Many great civilizations have worshiped it, including the Aztecs and the ancient Egyptians. Sun gods have had many names in these religions, myths and legends. To the Egyptians it was Ra while to the ancient Greeks it was Helios.
This diagram shows the different zones of the Sun, from its core out to the corona.
Until relatively recently (the early 16th century) most people thought the Sun went around the Earth. Then, in 1514, the astronomer Copernicus published his findings, proving that in fact the Earth orbits the Sun.
You can watch a short video clip of the Sun rotating which was captured by the SOHO (Solar and Heliospheric Observatory) spacecraft.
Images, information and videos courtesy of NASA.