The Sun is the closest star to Earth and the centre of our
Solar System. This vast ball consists of hot luminous
gas kept together by gravity. About three quarters is
hydrogen and almost all the rest is helium, with
small amounts of about 90 other elements. More
than half of the gas is squashed in the Sun’s
core where nuclear reactions convert
hydrogen to helium and in the process
produce huge amounts of energy. This
energy is released through the Sun’s
surface, most familiarly as heat and light.
The Sun has been producing energy in
this way for about 4.6 billion years and
will do so for another 5 billion or so.
This image shows the Sun not as
it appears to the human eye, but
in ultraviolet light.Sun
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(^1) SIZE
The Sun is the largest body in
the Solar System. It measures
1.4 million km (870,000 miles)
in diameter, which means that
109 Earths could fit across its face.
The Sun is made of 330,000 times
more material than Earth, and
1.3 million Earths would fit inside it.
(^2) PHOTOSPHERE
Like other stars, the Sun is not solid but
has a visible surface called the photosphere –
a violent place where jets and flares of gas
constantly shoot into space. It is made of
1,000-km (620-mile) wide short-lived granules of
rising gas, which together resemble orange peel.
(^3) TEMPERATURE
The temperature of the surface is 5,500°C (9,900°F),
and it is this that gives the Sun its yellow colour.
Cooler stars are red, hotter ones are white. Inside is
much hotter. The core is 15 million°C (27 million°F)
and nuclear reactions here convert 600 million tonnes
of hydrogen to helium every second.
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